From cb4aecb9c872f13103a21e05f96ef57ef8397b7a Mon Sep 17 00:00:00 2001
From: Michael Hoennig <michael.hoennig@hostsharing.net>
Date: Thu, 26 Sep 2024 10:51:27 +0200
Subject: [PATCH] refactoring for implicit creation of dependend hosting-assets
 (#108)

Co-authored-by: Michael Hoennig <michael@hoennig.de>
Reviewed-on: https://dev.hostsharing.net/hostsharing/hs.hsadmin.ng/pulls/108
Reviewed-by: Timotheus Pokorra <timotheus.pokorra@hostsharing.net>
---
 README.md                                     |  27 +++-
 .../hsadminng/errors/DisplayAs.java           |  12 +-
 .../booking/item/HsBookingItemController.java |  37 +++--
 .../BookingItemEntitySaveProcessor.java       | 131 ++++++++++++++++++
 .../HsBookingItemEntityValidatorRegistry.java |   5 +-
 .../HsDomainSetupBookingItemValidator.java    |  10 ++
 .../project/HsBookingProjectController.java   |   4 +-
 .../asset/HsHostingAssetController.java       |   4 +-
 .../HsOfficeBankAccountController.java        |   4 +-
 .../contact/HsOfficeContactController.java    |   4 +-
 ...OfficeCoopAssetsTransactionController.java |   4 +-
 ...OfficeCoopSharesTransactionController.java |   4 +-
 .../debitor/HsOfficeDebitorController.java    |  29 ++--
 .../HsOfficeMembershipController.java         |   4 +-
 .../HsOfficeMembershipEntityPatcher.java      |   6 +-
 .../partner/HsOfficePartnerController.java    |   4 +-
 .../person/HsOfficePersonController.java      |   4 +-
 .../relation/HsOfficeRelationController.java  |   4 +-
 .../HsOfficeSepaMandateController.java        |   4 +-
 .../hs/validation/HsEntityValidator.java      |   2 +-
 .../hostsharing/hsadminng/mapper/Mapper.java  |  43 ++++--
 .../hsadminng/mapper/MapperConfiguration.java |  13 --
 .../hsadminng/mapper/StandardMapper.java      |  14 ++
 .../hsadminng/mapper/StrictMapper.java        |  19 +++
 .../persistence/EntityExistsValidator.java    |  39 ++++++
 .../rbac/grant/RbacGrantController.java       |   4 +-
 .../rbac/role/RbacRoleController.java         |   4 +-
 .../rbac/subject/RbacSubjectController.java   |   4 +-
 .../test/cust/TestCustomerController.java     |   4 +-
 .../rbac/test/pac/TestPackageController.java  |   4 +-
 .../item/HsBookingItemControllerRestTest.java |  28 +++-
 ...mainSetupBookingItemValidatorUnitTest.java |  55 +++++++-
 .../HsHostingAssetControllerRestTest.java     |  10 +-
 ...ainSetupHostingAssetValidatorUnitTest.java |   3 +-
 .../hs/migration/ImportHostingAssets.java     |   8 +-
 ...HsOfficeBankAccountControllerRestTest.java |   4 +-
 ...opAssetsTransactionControllerRestTest.java |   4 +-
 ...opSharesTransactionControllerRestTest.java |   4 +-
 ...OfficeDebitorControllerAcceptanceTest.java |   2 +-
 .../HsOfficeMembershipControllerRestTest.java |   6 +-
 ...OfficeMembershipEntityPatcherUnitTest.java |   4 +-
 .../HsOfficePartnerControllerRestTest.java    |   4 +-
 ...ceSepaMandateControllerAcceptanceTest.java |   4 +-
 .../rbac/context/ContextIntegrationTests.java |   4 +-
 .../rbac/role/RbacRoleControllerRestTest.java |   4 +-
 .../RbacSubjectControllerRestTest.java        |   4 +-
 .../hsadminng/rbac/test/MapperUnitTest.java   |  14 +-
 47 files changed, 474 insertions(+), 139 deletions(-)
 create mode 100644 src/main/java/net/hostsharing/hsadminng/hs/booking/item/validators/BookingItemEntitySaveProcessor.java
 delete mode 100644 src/main/java/net/hostsharing/hsadminng/mapper/MapperConfiguration.java
 create mode 100644 src/main/java/net/hostsharing/hsadminng/mapper/StandardMapper.java
 create mode 100644 src/main/java/net/hostsharing/hsadminng/mapper/StrictMapper.java
 create mode 100644 src/main/java/net/hostsharing/hsadminng/persistence/EntityExistsValidator.java

diff --git a/README.md b/README.md
index 37777227..e1d1515b 100644
--- a/README.md
+++ b/README.md
@@ -550,12 +550,37 @@ Dependency versions can be automatically upgraded to the latest available versio
 gw useLatestVersions
 ```
 
-Afterwards, `gw check` is automatically started.
+Afterward, `gw check` is automatically started.
 Please only commit+push to master if the check run shows no errors.
 
 More infos, e.g. on blacklists see on the [project's website](https://github.com/patrikerdes/gradle-use-latest-versions-plugin).
 
 
+## Biggest Flaws in our Architecture
+
+### The RBAC System is too Complicated
+
+Now, where we have a better experience with what we really need from the RBAC system, we have learned
+that and creates too many (grant- and role-) rows and too even tables which could be avoided completely.
+
+The basic idea is always to always have a fixed set of ordered role-types which apply for all DB-tables under RBAC,
+e.g. OWNER>ADMIN>AGENT\[>PROXY?\]>TENENT>REFERRER.
+Grants between these for the same DB-row would be implicit by order comparision.
+This way we would get rid of all explicit grants within the same DB-row
+and would not need the `rbac.role` table anymore.
+We would also reduce the depth of the expensive recursive CTE-query.
+
+This has to be explored further.
+For now, we just keep it in mind and  
+
+### The Mapper is Error-Prone
+
+Where `org.modelmapper.ModelMapper` reduces bloat-code a lot and has some nice features about recursive data-structure mappings,
+it often causes strange errors which are hard to fix.
+E.g. the uuid of the target main object is often taken from an uuid of a sub-subject.
+(For now, use `StrictMapper` to avoid this, for the case it happens.)
+
+
 ## How To ...
 
 ### How to Configure .pgpass for the Default PostgreSQL Database?
diff --git a/src/main/java/net/hostsharing/hsadminng/errors/DisplayAs.java b/src/main/java/net/hostsharing/hsadminng/errors/DisplayAs.java
index 020d006a..20723330 100644
--- a/src/main/java/net/hostsharing/hsadminng/errors/DisplayAs.java
+++ b/src/main/java/net/hostsharing/hsadminng/errors/DisplayAs.java
@@ -9,15 +9,25 @@ import java.lang.annotation.Target;
 @Target(ElementType.TYPE)
 @Retention(RetentionPolicy.RUNTIME)
 public @interface DisplayAs {
+
     class DisplayName {
+
         public static String of(final Class<?> clazz) {
-            final var displayNameAnnot = clazz.getAnnotation(DisplayAs.class);
+            final var displayNameAnnot = getDisplayNameAnnotation(clazz);
             return displayNameAnnot != null ? displayNameAnnot.value() : clazz.getSimpleName();
         }
 
         public static String of(@NotNull final Object instance) {
             return of(instance.getClass());
         }
+
+        private static DisplayAs getDisplayNameAnnotation(final Class<?> clazz) {
+            if (clazz == null) {
+                return null;
+            }
+            final var annot = clazz.getAnnotation(DisplayAs.class);
+            return annot != null ? annot : getDisplayNameAnnotation(clazz.getSuperclass());
+        }
     }
 
     String value() default "";
diff --git a/src/main/java/net/hostsharing/hsadminng/hs/booking/item/HsBookingItemController.java b/src/main/java/net/hostsharing/hsadminng/hs/booking/item/HsBookingItemController.java
index 6afd5219..84f35054 100644
--- a/src/main/java/net/hostsharing/hsadminng/hs/booking/item/HsBookingItemController.java
+++ b/src/main/java/net/hostsharing/hsadminng/hs/booking/item/HsBookingItemController.java
@@ -5,17 +5,18 @@ import net.hostsharing.hsadminng.hs.booking.generated.api.v1.api.HsBookingItemsA
 import net.hostsharing.hsadminng.hs.booking.generated.api.v1.model.HsBookingItemInsertResource;
 import net.hostsharing.hsadminng.hs.booking.generated.api.v1.model.HsBookingItemPatchResource;
 import net.hostsharing.hsadminng.hs.booking.generated.api.v1.model.HsBookingItemResource;
+import net.hostsharing.hsadminng.hs.booking.item.validators.BookingItemEntitySaveProcessor;
 import net.hostsharing.hsadminng.hs.booking.item.validators.HsBookingItemEntityValidatorRegistry;
+import net.hostsharing.hsadminng.hs.booking.project.HsBookingProjectRealEntity;
 import net.hostsharing.hsadminng.mapper.KeyValueMap;
-import net.hostsharing.hsadminng.mapper.Mapper;
+import net.hostsharing.hsadminng.mapper.StrictMapper;
+import net.hostsharing.hsadminng.persistence.EntityManagerWrapper;
 import org.springframework.beans.factory.annotation.Autowired;
 import org.springframework.http.ResponseEntity;
 import org.springframework.transaction.annotation.Transactional;
 import org.springframework.web.bind.annotation.RestController;
 import org.springframework.web.servlet.mvc.method.annotation.MvcUriComponentsBuilder;
 
-import jakarta.persistence.EntityManager;
-import jakarta.persistence.PersistenceContext;
 import java.time.LocalDate;
 import java.util.List;
 import java.util.UUID;
@@ -30,13 +31,13 @@ public class HsBookingItemController implements HsBookingItemsApi {
     private Context context;
 
     @Autowired
-    private Mapper mapper;
+    private StrictMapper mapper;
 
     @Autowired
     private HsBookingItemRbacRepository bookingItemRepo;
 
-    @PersistenceContext
-    private EntityManager em;
+    @Autowired
+    private EntityManagerWrapper em;
 
     @Override
     @Transactional(readOnly = true)
@@ -48,7 +49,7 @@ public class HsBookingItemController implements HsBookingItemsApi {
 
         final var entities = bookingItemRepo.findAllByProjectUuid(projectUuid);
 
-        final var resources = mapper.mapList(entities, HsBookingItemResource.class, ENTITY_TO_RESOURCE_POSTMAPPER);
+        final var resources = mapper.mapList(entities, HsBookingItemResource.class, RBAC_ENTITY_TO_RESOURCE_POSTMAPPER);
         return ResponseEntity.ok(resources);
     }
 
@@ -62,15 +63,20 @@ public class HsBookingItemController implements HsBookingItemsApi {
         context.define(currentSubject, assumedRoles);
 
         final var entityToSave = mapper.map(body, HsBookingItemRbacEntity.class, RESOURCE_TO_ENTITY_POSTMAPPER);
-
-        final var saved = HsBookingItemEntityValidatorRegistry.validated(em, bookingItemRepo.save(entityToSave));
+        final var mapped = new BookingItemEntitySaveProcessor(em, entityToSave)
+                .preprocessEntity()
+                .validateEntity()
+                .prepareForSave()
+                .save()
+                .validateContext()
+                .mapUsing(e -> mapper.map(e, HsBookingItemResource.class, ITEM_TO_RESOURCE_POSTMAPPER))
+                .revampProperties();
 
         final var uri =
                 MvcUriComponentsBuilder.fromController(getClass())
                         .path("/api/hs/booking/items/{id}")
-                        .buildAndExpand(saved.getUuid())
+                        .buildAndExpand(mapped.getUuid())
                         .toUri();
-        final var mapped = mapper.map(saved, HsBookingItemResource.class, ENTITY_TO_RESOURCE_POSTMAPPER);
         return ResponseEntity.created(uri).body(mapped);
     }
 
@@ -87,7 +93,7 @@ public class HsBookingItemController implements HsBookingItemsApi {
         result.ifPresent(entity -> em.detach(entity)); // prevent further LAZY-loading
         return result
                 .map(bookingItemEntity -> ResponseEntity.ok(
-                        mapper.map(bookingItemEntity, HsBookingItemResource.class, ENTITY_TO_RESOURCE_POSTMAPPER)))
+                        mapper.map(bookingItemEntity, HsBookingItemResource.class, RBAC_ENTITY_TO_RESOURCE_POSTMAPPER)))
                 .orElseGet(() -> ResponseEntity.notFound().build());
     }
 
@@ -120,18 +126,21 @@ public class HsBookingItemController implements HsBookingItemsApi {
         new HsBookingItemEntityPatcher(current).apply(body);
 
         final var saved = bookingItemRepo.save(HsBookingItemEntityValidatorRegistry.validated(em, current));
-        final var mapped = mapper.map(saved, HsBookingItemResource.class, ENTITY_TO_RESOURCE_POSTMAPPER);
+        final var mapped = mapper.map(saved, HsBookingItemResource.class, RBAC_ENTITY_TO_RESOURCE_POSTMAPPER);
         return ResponseEntity.ok(mapped);
     }
 
-    final BiConsumer<HsBookingItemRbacEntity, HsBookingItemResource> ENTITY_TO_RESOURCE_POSTMAPPER = (entity, resource) -> {
+    final BiConsumer<HsBookingItem, HsBookingItemResource> ITEM_TO_RESOURCE_POSTMAPPER = (entity, resource) -> {
         resource.setValidFrom(entity.getValidity().lower());
         if (entity.getValidity().hasUpperBound()) {
             resource.setValidTo(entity.getValidity().upper().minusDays(1));
         }
     };
 
+    final BiConsumer<HsBookingItemRbacEntity, HsBookingItemResource> RBAC_ENTITY_TO_RESOURCE_POSTMAPPER = ITEM_TO_RESOURCE_POSTMAPPER::accept;
+
     final BiConsumer<HsBookingItemInsertResource, HsBookingItemRbacEntity> RESOURCE_TO_ENTITY_POSTMAPPER = (resource, entity) -> {
+        entity.setProject(em.find(HsBookingProjectRealEntity.class, resource.getProjectUuid()));
         entity.setValidity(toPostgresDateRange(LocalDate.now(), resource.getValidTo()));
         entity.putResources(KeyValueMap.from(resource.getResources()));
     };
diff --git a/src/main/java/net/hostsharing/hsadminng/hs/booking/item/validators/BookingItemEntitySaveProcessor.java b/src/main/java/net/hostsharing/hsadminng/hs/booking/item/validators/BookingItemEntitySaveProcessor.java
new file mode 100644
index 00000000..77ce40ae
--- /dev/null
+++ b/src/main/java/net/hostsharing/hsadminng/hs/booking/item/validators/BookingItemEntitySaveProcessor.java
@@ -0,0 +1,131 @@
+package net.hostsharing.hsadminng.hs.booking.item.validators;
+
+import net.hostsharing.hsadminng.errors.MultiValidationException;
+import net.hostsharing.hsadminng.hs.booking.generated.api.v1.model.HsBookingItemResource;
+import net.hostsharing.hsadminng.hs.booking.item.HsBookingItem;
+import net.hostsharing.hsadminng.hs.validation.HsEntityValidator;
+
+import jakarta.persistence.EntityManager;
+import java.util.Arrays;
+import java.util.Map;
+import java.util.function.Function;
+import java.util.regex.Pattern;
+
+// TODO.refa: introduce common base class with HsHostingAssetEntitySaveProcessor
+/**
+ * Wraps the steps of the pararation, validation, mapping and revamp around saving of a HsBookingItem into a readable API.
+ */
+public class BookingItemEntitySaveProcessor {
+
+    private final HsEntityValidator<HsBookingItem> validator;
+    private String expectedStep = "preprocessEntity";
+    private final EntityManager em;
+    private HsBookingItem entity;
+    private HsBookingItemResource resource;
+
+    public BookingItemEntitySaveProcessor(final EntityManager em, final HsBookingItem entity) {
+        this.em = em;
+        this.entity = entity;
+        this.validator = HsBookingItemEntityValidatorRegistry.forType(entity.getType());
+    }
+
+    /// initial step allowing to set default values before any validations
+    public BookingItemEntitySaveProcessor preprocessEntity() {
+        step("preprocessEntity", "validateEntity");
+        validator.preprocessEntity(entity);
+        return this;
+    }
+
+    /// validates the entity itself including its properties
+    public BookingItemEntitySaveProcessor validateEntity() {
+        step("validateEntity", "prepareForSave");
+        MultiValidationException.throwIfNotEmpty(validator.validateEntity(entity));
+        return this;
+    }
+
+    // TODO.impl: remove once the migration of legacy data is done
+    /// validates the entity itself including its properties, but ignoring some error messages for import of legacy data
+    public BookingItemEntitySaveProcessor validateEntityIgnoring(final String... ignoreRegExp) {
+        step("validateEntity", "prepareForSave");
+        final var ignoreRegExpPatterns = Arrays.stream(ignoreRegExp).map(Pattern::compile).toList();
+        MultiValidationException.throwIfNotEmpty(
+                validator.validateEntity(entity).stream()
+                        .filter(error -> ignoreRegExpPatterns.stream().noneMatch(p -> p.matcher(error).matches() ))
+                        .toList()
+        );
+        return this;
+    }
+
+    /// hashing passwords etc.
+    public BookingItemEntitySaveProcessor prepareForSave() {
+        step("prepareForSave", "save");
+        validator.prepareProperties(em, entity);
+        return this;
+    }
+
+    /**
+     * Saves the entity using the given `saveFunction`.
+     *
+     * <p>`validator.postPersist(em, entity)` is NOT called.
+     * If any postprocessing is necessary, the saveFunction has to implement this.</p>
+     * @param saveFunction
+     * @return this
+     */
+    public BookingItemEntitySaveProcessor saveUsing(final Function<HsBookingItem, HsBookingItem> saveFunction) {
+        step("save", "validateContext");
+        entity = saveFunction.apply(entity);
+        return this;
+    }
+
+    /**
+     * Saves the using the `EntityManager`, but does NOT ever merge the entity.
+     *
+     * <p>`validator.postPersist(em, entity)` is called afterwards with the entity guaranteed to be flushed to the database.</p>
+     * @return this
+     */
+    public BookingItemEntitySaveProcessor save() {
+        return saveUsing(e -> {
+            if (!em.contains(entity)) {
+                em.persist(entity);
+            }
+            em.flush(); // makes RbacEntity available as RealEntity if needed
+            validator.postPersist(em, entity);
+            return entity;
+        });
+    }
+
+    /// validates the entity within it's parent and child hierarchy (e.g. totals validators and other limits)
+    public BookingItemEntitySaveProcessor validateContext() {
+        step("validateContext", "mapUsing");
+        return HsEntityValidator.doWithEntityManager(em, () -> {
+            MultiValidationException.throwIfNotEmpty(validator.validateContext(entity));
+            return this;
+        });
+    }
+
+    /// maps entity to JSON resource representation
+    public BookingItemEntitySaveProcessor mapUsing(
+            final Function<HsBookingItem, HsBookingItemResource> mapFunction) {
+        step("mapUsing", "revampProperties");
+        resource = mapFunction.apply(entity);
+        return this;
+    }
+
+    /// removes write-only-properties and ads computed-properties
+    @SuppressWarnings("unchecked")
+    public HsBookingItemResource revampProperties() {
+        step("revampProperties", null);
+        final var revampedProps = validator.revampProperties(em, entity, (Map<String, Object>) resource.getResources());
+        resource.setResources(revampedProps);
+        return resource;
+    }
+
+    // Makes sure that the steps are called in the correct order.
+    // Could also be implemented using an interface per method, but that seems exaggerated.
+    private void step(final String current, final String next) {
+        if (!expectedStep.equals(current)) {
+            throw new IllegalStateException("expected " + expectedStep + " but got " + current);
+        }
+        expectedStep = next;
+    }
+}
diff --git a/src/main/java/net/hostsharing/hsadminng/hs/booking/item/validators/HsBookingItemEntityValidatorRegistry.java b/src/main/java/net/hostsharing/hsadminng/hs/booking/item/validators/HsBookingItemEntityValidatorRegistry.java
index 8bfe12fd..6567ae83 100644
--- a/src/main/java/net/hostsharing/hsadminng/hs/booking/item/validators/HsBookingItemEntityValidatorRegistry.java
+++ b/src/main/java/net/hostsharing/hsadminng/hs/booking/item/validators/HsBookingItemEntityValidatorRegistry.java
@@ -48,10 +48,11 @@ public class HsBookingItemEntityValidatorRegistry {
     }
 
     public static List<String> doValidate(final EntityManager em, final HsBookingItem bookingItem) {
+        final var bookingItemValidator = HsBookingItemEntityValidatorRegistry.forType(bookingItem.getType());
         return HsEntityValidator.doWithEntityManager(em, () ->
             HsEntityValidator.sequentiallyValidate(
-                    () -> HsBookingItemEntityValidatorRegistry.forType(bookingItem.getType()).validateEntity(bookingItem),
-                    () -> HsBookingItemEntityValidatorRegistry.forType(bookingItem.getType()).validateContext(bookingItem))
+                    () -> bookingItemValidator.validateEntity(bookingItem),
+                    () -> bookingItemValidator.validateContext(bookingItem))
         );
     }
 
diff --git a/src/main/java/net/hostsharing/hsadminng/hs/booking/item/validators/HsDomainSetupBookingItemValidator.java b/src/main/java/net/hostsharing/hsadminng/hs/booking/item/validators/HsDomainSetupBookingItemValidator.java
index c9fd731a..f42ea4e0 100644
--- a/src/main/java/net/hostsharing/hsadminng/hs/booking/item/validators/HsDomainSetupBookingItemValidator.java
+++ b/src/main/java/net/hostsharing/hsadminng/hs/booking/item/validators/HsDomainSetupBookingItemValidator.java
@@ -1,3 +1,4 @@
+
 package net.hostsharing.hsadminng.hs.booking.item.validators;
 
 import net.hostsharing.hsadminng.hs.booking.item.HsBookingItem;
@@ -15,6 +16,9 @@ class HsDomainSetupBookingItemValidator extends HsBookingItemEntityValidator {
 
     public static final String FQDN_REGEX = "^((?!-)[A-Za-z0-9-]{1,63}(?<!-)\\.)+[A-Za-z]{2,12}";
     public static final String DOMAIN_NAME_PROPERTY_NAME = "domainName";
+    public static final String TARGET_UNIX_USER_PROPERTY_NAME = "targetUnixUser";
+    public static final String WEBSPACE_NAME_REGEX = "[a-z][a-z0-9]{2}[0-9]{2}";
+    public static final String TARGET_UNIX_USER_NAME_REGEX = "^"+WEBSPACE_NAME_REGEX+"$|^"+WEBSPACE_NAME_REGEX+"-[a-z0-9\\._-]+$";
     public static final String VERIFICATION_CODE_PROPERTY_NAME = "verificationCode";
 
     HsDomainSetupBookingItemValidator() {
@@ -24,6 +28,12 @@ class HsDomainSetupBookingItemValidator extends HsBookingItemEntityValidator {
                         .matchesRegEx(FQDN_REGEX).describedAs("is not a (non-top-level) fully qualified domain name")
                         .notMatchesRegEx(REGISTRAR_LEVEL_DOMAINS).describedAs("is a forbidden registrar-level domain name")
                         .required(),
+                // TODO.legacy: remove the following property once we give up legacy compatibility
+                stringProperty(TARGET_UNIX_USER_PROPERTY_NAME).writeOnce()
+                        .maxLength(253)
+                        .matchesRegEx(TARGET_UNIX_USER_NAME_REGEX).describedAs("is not a valid unix-user name")
+                        .writeOnce()
+                        .required(),
                 stringProperty(VERIFICATION_CODE_PROPERTY_NAME)
                         .minLength(12)
                         .maxLength(64)
diff --git a/src/main/java/net/hostsharing/hsadminng/hs/booking/project/HsBookingProjectController.java b/src/main/java/net/hostsharing/hsadminng/hs/booking/project/HsBookingProjectController.java
index 55d26b36..f657d45e 100644
--- a/src/main/java/net/hostsharing/hsadminng/hs/booking/project/HsBookingProjectController.java
+++ b/src/main/java/net/hostsharing/hsadminng/hs/booking/project/HsBookingProjectController.java
@@ -6,7 +6,7 @@ import net.hostsharing.hsadminng.hs.booking.generated.api.v1.api.HsBookingProjec
 import net.hostsharing.hsadminng.hs.booking.generated.api.v1.model.HsBookingProjectInsertResource;
 import net.hostsharing.hsadminng.hs.booking.generated.api.v1.model.HsBookingProjectPatchResource;
 import net.hostsharing.hsadminng.hs.booking.generated.api.v1.model.HsBookingProjectResource;
-import net.hostsharing.hsadminng.mapper.Mapper;
+import net.hostsharing.hsadminng.mapper.StandardMapper;
 import org.springframework.beans.factory.annotation.Autowired;
 import org.springframework.http.ResponseEntity;
 import org.springframework.transaction.annotation.Transactional;
@@ -25,7 +25,7 @@ public class HsBookingProjectController implements HsBookingProjectsApi {
     private Context context;
 
     @Autowired
-    private Mapper mapper;
+    private StandardMapper mapper;
 
     @Autowired
     private HsBookingProjectRbacRepository bookingProjectRepo;
diff --git a/src/main/java/net/hostsharing/hsadminng/hs/hosting/asset/HsHostingAssetController.java b/src/main/java/net/hostsharing/hsadminng/hs/hosting/asset/HsHostingAssetController.java
index 8973d0cc..56b59427 100644
--- a/src/main/java/net/hostsharing/hsadminng/hs/hosting/asset/HsHostingAssetController.java
+++ b/src/main/java/net/hostsharing/hsadminng/hs/hosting/asset/HsHostingAssetController.java
@@ -11,7 +11,7 @@ import net.hostsharing.hsadminng.hs.hosting.generated.api.v1.model.HsHostingAsse
 import net.hostsharing.hsadminng.hs.hosting.generated.api.v1.model.HsHostingAssetResource;
 import net.hostsharing.hsadminng.hs.hosting.generated.api.v1.model.HsHostingAssetTypeResource;
 import net.hostsharing.hsadminng.mapper.KeyValueMap;
-import net.hostsharing.hsadminng.mapper.Mapper;
+import net.hostsharing.hsadminng.mapper.StandardMapper;
 import net.hostsharing.hsadminng.persistence.EntityManagerWrapper;
 import org.springframework.beans.factory.annotation.Autowired;
 import org.springframework.http.ResponseEntity;
@@ -35,7 +35,7 @@ public class HsHostingAssetController implements HsHostingAssetsApi {
     private Context context;
 
     @Autowired
-    private Mapper mapper;
+    private StandardMapper mapper;
 
     @Autowired
     private HsHostingAssetRbacRepository rbacAssetRepo;
diff --git a/src/main/java/net/hostsharing/hsadminng/hs/office/bankaccount/HsOfficeBankAccountController.java b/src/main/java/net/hostsharing/hsadminng/hs/office/bankaccount/HsOfficeBankAccountController.java
index 50183bf7..69295853 100644
--- a/src/main/java/net/hostsharing/hsadminng/hs/office/bankaccount/HsOfficeBankAccountController.java
+++ b/src/main/java/net/hostsharing/hsadminng/hs/office/bankaccount/HsOfficeBankAccountController.java
@@ -4,7 +4,7 @@ import net.hostsharing.hsadminng.context.Context;
 import net.hostsharing.hsadminng.hs.office.generated.api.v1.api.HsOfficeBankAccountsApi;
 import net.hostsharing.hsadminng.hs.office.generated.api.v1.model.HsOfficeBankAccountInsertResource;
 import net.hostsharing.hsadminng.hs.office.generated.api.v1.model.HsOfficeBankAccountResource;
-import net.hostsharing.hsadminng.mapper.Mapper;
+import net.hostsharing.hsadminng.mapper.StandardMapper;
 import org.iban4j.BicUtil;
 import org.iban4j.IbanUtil;
 import org.springframework.beans.factory.annotation.Autowired;
@@ -24,7 +24,7 @@ public class HsOfficeBankAccountController implements HsOfficeBankAccountsApi {
     private Context context;
 
     @Autowired
-    private Mapper mapper;
+    private StandardMapper mapper;
 
     @Autowired
     private HsOfficeBankAccountRepository bankAccountRepo;
diff --git a/src/main/java/net/hostsharing/hsadminng/hs/office/contact/HsOfficeContactController.java b/src/main/java/net/hostsharing/hsadminng/hs/office/contact/HsOfficeContactController.java
index 17d39b7f..0f94e858 100644
--- a/src/main/java/net/hostsharing/hsadminng/hs/office/contact/HsOfficeContactController.java
+++ b/src/main/java/net/hostsharing/hsadminng/hs/office/contact/HsOfficeContactController.java
@@ -1,6 +1,6 @@
 package net.hostsharing.hsadminng.hs.office.contact;
 
-import net.hostsharing.hsadminng.mapper.Mapper;
+import net.hostsharing.hsadminng.mapper.StandardMapper;
 import net.hostsharing.hsadminng.context.Context;
 import net.hostsharing.hsadminng.hs.office.generated.api.v1.api.HsOfficeContactsApi;
 import net.hostsharing.hsadminng.hs.office.generated.api.v1.model.HsOfficeContactInsertResource;
@@ -26,7 +26,7 @@ public class HsOfficeContactController implements HsOfficeContactsApi {
     private Context context;
 
     @Autowired
-    private Mapper mapper;
+    private StandardMapper mapper;
 
     @Autowired
     private HsOfficeContactRbacRepository contactRepo;
diff --git a/src/main/java/net/hostsharing/hsadminng/hs/office/coopassets/HsOfficeCoopAssetsTransactionController.java b/src/main/java/net/hostsharing/hsadminng/hs/office/coopassets/HsOfficeCoopAssetsTransactionController.java
index f4cb28a3..9154b8f0 100644
--- a/src/main/java/net/hostsharing/hsadminng/hs/office/coopassets/HsOfficeCoopAssetsTransactionController.java
+++ b/src/main/java/net/hostsharing/hsadminng/hs/office/coopassets/HsOfficeCoopAssetsTransactionController.java
@@ -4,7 +4,7 @@ import net.hostsharing.hsadminng.context.Context;
 import net.hostsharing.hsadminng.hs.office.generated.api.v1.api.HsOfficeCoopAssetsApi;
 import net.hostsharing.hsadminng.hs.office.generated.api.v1.model.*;
 import net.hostsharing.hsadminng.errors.MultiValidationException;
-import net.hostsharing.hsadminng.mapper.Mapper;
+import net.hostsharing.hsadminng.mapper.StandardMapper;
 import org.springframework.beans.factory.annotation.Autowired;
 import org.springframework.format.annotation.DateTimeFormat;
 import org.springframework.format.annotation.DateTimeFormat.ISO;
@@ -29,7 +29,7 @@ public class HsOfficeCoopAssetsTransactionController implements HsOfficeCoopAsse
     private Context context;
 
     @Autowired
-    private Mapper mapper;
+    private StandardMapper mapper;
 
     @Autowired
     private HsOfficeCoopAssetsTransactionRepository coopAssetsTransactionRepo;
diff --git a/src/main/java/net/hostsharing/hsadminng/hs/office/coopshares/HsOfficeCoopSharesTransactionController.java b/src/main/java/net/hostsharing/hsadminng/hs/office/coopshares/HsOfficeCoopSharesTransactionController.java
index 1616568d..6712fefd 100644
--- a/src/main/java/net/hostsharing/hsadminng/hs/office/coopshares/HsOfficeCoopSharesTransactionController.java
+++ b/src/main/java/net/hostsharing/hsadminng/hs/office/coopshares/HsOfficeCoopSharesTransactionController.java
@@ -6,7 +6,7 @@ import net.hostsharing.hsadminng.hs.office.generated.api.v1.api.HsOfficeCoopShar
 import net.hostsharing.hsadminng.hs.office.generated.api.v1.model.HsOfficeCoopSharesTransactionInsertResource;
 import net.hostsharing.hsadminng.hs.office.generated.api.v1.model.HsOfficeCoopSharesTransactionResource;
 import net.hostsharing.hsadminng.errors.MultiValidationException;
-import net.hostsharing.hsadminng.mapper.Mapper;
+import net.hostsharing.hsadminng.mapper.StandardMapper;
 import org.springframework.beans.factory.annotation.Autowired;
 import org.springframework.format.annotation.DateTimeFormat;
 import org.springframework.format.annotation.DateTimeFormat.ISO;
@@ -31,7 +31,7 @@ public class HsOfficeCoopSharesTransactionController implements HsOfficeCoopShar
     private Context context;
 
     @Autowired
-    private Mapper mapper;
+    private StandardMapper mapper;
 
     @Autowired
     private HsOfficeCoopSharesTransactionRepository coopSharesTransactionRepo;
diff --git a/src/main/java/net/hostsharing/hsadminng/hs/office/debitor/HsOfficeDebitorController.java b/src/main/java/net/hostsharing/hsadminng/hs/office/debitor/HsOfficeDebitorController.java
index fd8412c8..0770aa35 100644
--- a/src/main/java/net/hostsharing/hsadminng/hs/office/debitor/HsOfficeDebitorController.java
+++ b/src/main/java/net/hostsharing/hsadminng/hs/office/debitor/HsOfficeDebitorController.java
@@ -7,8 +7,8 @@ import net.hostsharing.hsadminng.hs.office.generated.api.v1.model.HsOfficeDebito
 import net.hostsharing.hsadminng.hs.office.generated.api.v1.model.HsOfficeDebitorResource;
 import net.hostsharing.hsadminng.hs.office.relation.HsOfficeRelationRealEntity;
 import net.hostsharing.hsadminng.hs.office.relation.HsOfficeRelationRealRepository;
-import net.hostsharing.hsadminng.mapper.Mapper;
-import net.hostsharing.hsadminng.rbac.object.BaseEntity;
+import net.hostsharing.hsadminng.mapper.StandardMapper;
+import net.hostsharing.hsadminng.persistence.EntityExistsValidator;
 import org.apache.commons.lang3.Validate;
 import org.hibernate.Hibernate;
 import org.springframework.beans.factory.annotation.Autowired;
@@ -23,7 +23,6 @@ import jakarta.validation.ValidationException;
 import java.util.List;
 import java.util.UUID;
 
-import static net.hostsharing.hsadminng.errors.DisplayAs.DisplayName;
 import static net.hostsharing.hsadminng.hs.office.relation.HsOfficeRelationType.DEBITOR;
 
 @RestController
@@ -34,7 +33,7 @@ public class HsOfficeDebitorController implements HsOfficeDebitorsApi {
     private Context context;
 
     @Autowired
-    private Mapper mapper;
+    private StandardMapper mapper;
 
     @Autowired
     private HsOfficeDebitorRepository debitorRepo;
@@ -42,6 +41,9 @@ public class HsOfficeDebitorController implements HsOfficeDebitorsApi {
     @Autowired
     private HsOfficeRelationRealRepository relrealRepo;
 
+    @Autowired
+    private EntityExistsValidator entityValidator;
+
     @PersistenceContext
     private EntityManager em;
 
@@ -84,10 +86,10 @@ public class HsOfficeDebitorController implements HsOfficeDebitorsApi {
         final var entityToSave = mapper.map(body, HsOfficeDebitorEntity.class);
         if ( body.getDebitorRel() != null ) {
             body.getDebitorRel().setType(DEBITOR.name());
-            final var debitorRel = mapper.map(body.getDebitorRel(), HsOfficeRelationRealEntity.class);
-            validateEntityExists("debitorRel.anchorUuid", debitorRel.getAnchor());
-            validateEntityExists("debitorRel.holderUuid", debitorRel.getHolder());
-            validateEntityExists("debitorRel.contactUuid", debitorRel.getContact());
+            final var debitorRel = mapper.map("debitorRel.", body.getDebitorRel(), HsOfficeRelationRealEntity.class);
+            entityValidator.validateEntityExists("debitorRel.anchorUuid", debitorRel.getAnchor());
+            entityValidator.validateEntityExists("debitorRel.holderUuid", debitorRel.getHolder());
+            entityValidator.validateEntityExists("debitorRel.contactUuid", debitorRel.getContact());
             entityToSave.setDebitorRel(relrealRepo.save(debitorRel));
         } else {
             final var debitorRelOptional = relrealRepo.findByUuid(body.getDebitorRelUuid());
@@ -160,15 +162,4 @@ public class HsOfficeDebitorController implements HsOfficeDebitorsApi {
         final var mapped = mapper.map(saved, HsOfficeDebitorResource.class);
         return ResponseEntity.ok(mapped);
     }
-
-    // TODO.impl: extract this to some generally usable class?
-    private <T extends BaseEntity<T>> T validateEntityExists(final String property, final T entitySkeleton) {
-        final var foundEntity = em.find(entitySkeleton.getClass(), entitySkeleton.getUuid());
-        if ( foundEntity == null) {
-            throw new ValidationException("Unable to find " + DisplayName.of(entitySkeleton) + " by " + property + ": " + entitySkeleton.getUuid());
-        }
-
-        //noinspection unchecked
-        return (T) foundEntity;
-    }
 }
diff --git a/src/main/java/net/hostsharing/hsadminng/hs/office/membership/HsOfficeMembershipController.java b/src/main/java/net/hostsharing/hsadminng/hs/office/membership/HsOfficeMembershipController.java
index 8c87e5fa..d63f9e6a 100644
--- a/src/main/java/net/hostsharing/hsadminng/hs/office/membership/HsOfficeMembershipController.java
+++ b/src/main/java/net/hostsharing/hsadminng/hs/office/membership/HsOfficeMembershipController.java
@@ -5,7 +5,7 @@ import net.hostsharing.hsadminng.hs.office.generated.api.v1.api.HsOfficeMembersh
 import net.hostsharing.hsadminng.hs.office.generated.api.v1.model.HsOfficeMembershipInsertResource;
 import net.hostsharing.hsadminng.hs.office.generated.api.v1.model.HsOfficeMembershipPatchResource;
 import net.hostsharing.hsadminng.hs.office.generated.api.v1.model.HsOfficeMembershipResource;
-import net.hostsharing.hsadminng.mapper.Mapper;
+import net.hostsharing.hsadminng.mapper.StandardMapper;
 import org.springframework.beans.factory.annotation.Autowired;
 import org.springframework.http.ResponseEntity;
 import org.springframework.transaction.annotation.Transactional;
@@ -24,7 +24,7 @@ public class HsOfficeMembershipController implements HsOfficeMembershipsApi {
     private Context context;
 
     @Autowired
-    private Mapper mapper;
+    private StandardMapper mapper;
 
     @Autowired
     private HsOfficeMembershipRepository membershipRepo;
diff --git a/src/main/java/net/hostsharing/hsadminng/hs/office/membership/HsOfficeMembershipEntityPatcher.java b/src/main/java/net/hostsharing/hsadminng/hs/office/membership/HsOfficeMembershipEntityPatcher.java
index cbecb800..33bf363b 100644
--- a/src/main/java/net/hostsharing/hsadminng/hs/office/membership/HsOfficeMembershipEntityPatcher.java
+++ b/src/main/java/net/hostsharing/hsadminng/hs/office/membership/HsOfficeMembershipEntityPatcher.java
@@ -2,18 +2,18 @@ package net.hostsharing.hsadminng.hs.office.membership;
 
 import net.hostsharing.hsadminng.hs.office.generated.api.v1.model.HsOfficeMembershipPatchResource;
 import net.hostsharing.hsadminng.mapper.EntityPatcher;
-import net.hostsharing.hsadminng.mapper.Mapper;
+import net.hostsharing.hsadminng.mapper.StandardMapper;
 import net.hostsharing.hsadminng.mapper.OptionalFromJson;
 
 import java.util.Optional;
 
 public class HsOfficeMembershipEntityPatcher implements EntityPatcher<HsOfficeMembershipPatchResource> {
 
-    private final Mapper mapper;
+    private final StandardMapper mapper;
     private final HsOfficeMembershipEntity entity;
 
     public HsOfficeMembershipEntityPatcher(
-            final Mapper mapper,
+            final StandardMapper mapper,
             final HsOfficeMembershipEntity entity) {
         this.mapper = mapper;
         this.entity = entity;
diff --git a/src/main/java/net/hostsharing/hsadminng/hs/office/partner/HsOfficePartnerController.java b/src/main/java/net/hostsharing/hsadminng/hs/office/partner/HsOfficePartnerController.java
index b4b8bd75..55c280f3 100644
--- a/src/main/java/net/hostsharing/hsadminng/hs/office/partner/HsOfficePartnerController.java
+++ b/src/main/java/net/hostsharing/hsadminng/hs/office/partner/HsOfficePartnerController.java
@@ -12,7 +12,7 @@ import net.hostsharing.hsadminng.hs.office.person.HsOfficePersonEntity;
 import net.hostsharing.hsadminng.hs.office.relation.HsOfficeRelationRealEntity;
 import net.hostsharing.hsadminng.hs.office.relation.HsOfficeRelationRealRepository;
 import net.hostsharing.hsadminng.hs.office.relation.HsOfficeRelationType;
-import net.hostsharing.hsadminng.mapper.Mapper;
+import net.hostsharing.hsadminng.mapper.StandardMapper;
 import net.hostsharing.hsadminng.rbac.object.BaseEntity;
 import org.springframework.beans.factory.annotation.Autowired;
 import org.springframework.http.HttpStatus;
@@ -36,7 +36,7 @@ public class HsOfficePartnerController implements HsOfficePartnersApi {
     private Context context;
 
     @Autowired
-    private Mapper mapper;
+    private StandardMapper mapper;
 
     @Autowired
     private HsOfficePartnerRepository partnerRepo;
diff --git a/src/main/java/net/hostsharing/hsadminng/hs/office/person/HsOfficePersonController.java b/src/main/java/net/hostsharing/hsadminng/hs/office/person/HsOfficePersonController.java
index 41d9d441..ac746aab 100644
--- a/src/main/java/net/hostsharing/hsadminng/hs/office/person/HsOfficePersonController.java
+++ b/src/main/java/net/hostsharing/hsadminng/hs/office/person/HsOfficePersonController.java
@@ -1,6 +1,6 @@
 package net.hostsharing.hsadminng.hs.office.person;
 
-import net.hostsharing.hsadminng.mapper.Mapper;
+import net.hostsharing.hsadminng.mapper.StandardMapper;
 import net.hostsharing.hsadminng.context.Context;
 import net.hostsharing.hsadminng.hs.office.generated.api.v1.api.HsOfficePersonsApi;
 import net.hostsharing.hsadminng.hs.office.generated.api.v1.model.HsOfficePersonInsertResource;
@@ -23,7 +23,7 @@ public class HsOfficePersonController implements HsOfficePersonsApi {
     private Context context;
 
     @Autowired
-    private Mapper mapper;
+    private StandardMapper mapper;
 
     @Autowired
     private HsOfficePersonRepository personRepo;
diff --git a/src/main/java/net/hostsharing/hsadminng/hs/office/relation/HsOfficeRelationController.java b/src/main/java/net/hostsharing/hsadminng/hs/office/relation/HsOfficeRelationController.java
index f054e563..b93537d9 100644
--- a/src/main/java/net/hostsharing/hsadminng/hs/office/relation/HsOfficeRelationController.java
+++ b/src/main/java/net/hostsharing/hsadminng/hs/office/relation/HsOfficeRelationController.java
@@ -5,7 +5,7 @@ import net.hostsharing.hsadminng.hs.office.contact.HsOfficeContactRealRepository
 import net.hostsharing.hsadminng.hs.office.generated.api.v1.api.HsOfficeRelationsApi;
 import net.hostsharing.hsadminng.hs.office.generated.api.v1.model.*;
 import net.hostsharing.hsadminng.hs.office.person.HsOfficePersonRepository;
-import net.hostsharing.hsadminng.mapper.Mapper;
+import net.hostsharing.hsadminng.mapper.StandardMapper;
 import org.springframework.beans.factory.annotation.Autowired;
 import org.springframework.http.ResponseEntity;
 import org.springframework.transaction.annotation.Transactional;
@@ -28,7 +28,7 @@ public class HsOfficeRelationController implements HsOfficeRelationsApi {
     private Context context;
 
     @Autowired
-    private Mapper mapper;
+    private StandardMapper mapper;
 
     @Autowired
     private HsOfficeRelationRbacRepository relationRbacRepo;
diff --git a/src/main/java/net/hostsharing/hsadminng/hs/office/sepamandate/HsOfficeSepaMandateController.java b/src/main/java/net/hostsharing/hsadminng/hs/office/sepamandate/HsOfficeSepaMandateController.java
index 9511bdd6..52ef2aad 100644
--- a/src/main/java/net/hostsharing/hsadminng/hs/office/sepamandate/HsOfficeSepaMandateController.java
+++ b/src/main/java/net/hostsharing/hsadminng/hs/office/sepamandate/HsOfficeSepaMandateController.java
@@ -5,7 +5,7 @@ import net.hostsharing.hsadminng.hs.office.generated.api.v1.api.HsOfficeSepaMand
 import net.hostsharing.hsadminng.hs.office.generated.api.v1.model.HsOfficeSepaMandateInsertResource;
 import net.hostsharing.hsadminng.hs.office.generated.api.v1.model.HsOfficeSepaMandatePatchResource;
 import net.hostsharing.hsadminng.hs.office.generated.api.v1.model.HsOfficeSepaMandateResource;
-import net.hostsharing.hsadminng.mapper.Mapper;
+import net.hostsharing.hsadminng.mapper.StandardMapper;
 import org.springframework.beans.factory.annotation.Autowired;
 import org.springframework.http.ResponseEntity;
 import org.springframework.transaction.annotation.Transactional;
@@ -28,7 +28,7 @@ public class HsOfficeSepaMandateController implements HsOfficeSepaMandatesApi {
     private Context context;
 
     @Autowired
-    private Mapper mapper;
+    private StandardMapper mapper;
 
     @Autowired
     private HsOfficeSepaMandateRepository sepaMandateRepo;
diff --git a/src/main/java/net/hostsharing/hsadminng/hs/validation/HsEntityValidator.java b/src/main/java/net/hostsharing/hsadminng/hs/validation/HsEntityValidator.java
index b2fa8a02..68f2779f 100644
--- a/src/main/java/net/hostsharing/hsadminng/hs/validation/HsEntityValidator.java
+++ b/src/main/java/net/hostsharing/hsadminng/hs/validation/HsEntityValidator.java
@@ -130,7 +130,7 @@ public abstract class HsEntityValidator<E extends PropertiesProvider> {
     }
 
     public Map<String, Object> revampProperties(final EntityManager em, final E entity, final Map<String, Object> config) {
-        final var copy = new HashMap<>(config);
+        final var copy = config != null ? new HashMap<>(config) : new HashMap();
         stream(propertyValidators).forEach(p -> {
             if (p.isWriteOnly()) {
                 copy.remove(p.propertyName);
diff --git a/src/main/java/net/hostsharing/hsadminng/mapper/Mapper.java b/src/main/java/net/hostsharing/hsadminng/mapper/Mapper.java
index 9fda5165..21779a5c 100644
--- a/src/main/java/net/hostsharing/hsadminng/mapper/Mapper.java
+++ b/src/main/java/net/hostsharing/hsadminng/mapper/Mapper.java
@@ -11,18 +11,20 @@ import java.lang.reflect.Field;
 import java.util.List;
 import java.util.function.BiConsumer;
 import java.util.stream.Collectors;
+import java.util.stream.Stream;
 
+import static java.util.Arrays.stream;
 import static net.hostsharing.hsadminng.errors.DisplayAs.DisplayName;
 
 /**
  * A nicer API for ModelMapper.
  */
-public class Mapper extends ModelMapper {
+abstract class Mapper extends ModelMapper {
 
     @PersistenceContext
     EntityManager em;
 
-    public Mapper() {
+    Mapper() {
         getConfiguration().setAmbiguityIgnored(true);
     }
 
@@ -45,8 +47,12 @@ public class Mapper extends ModelMapper {
 
     @Override
     public <D> D map(final Object source, final Class<D> destinationType) {
+        return map("", source, destinationType);
+    }
+
+    public <D> D map(final String namePrefix, final Object source, final Class<D> destinationType) {
         final var target = super.map(source, destinationType);
-        for (Field f : destinationType.getDeclaredFields()) {
+        for (Field f : getDeclaredFieldsIncludingSuperClasses(destinationType)) {
             if (f.getAnnotation(ManyToOne.class) == null) {
                 continue;
             }
@@ -64,18 +70,30 @@ public class Mapper extends ModelMapper {
             if (subEntityUuid == null) {
                 continue;
             }
-            ReflectionUtils.setField(f, target, findEntityById(f.getType(), subEntityUuid));
+            ReflectionUtils.setField(f, target, fetchEntity(namePrefix + f.getName() + ".uuid", f.getType(), subEntityUuid));
         }
         return target;
     }
 
-    private Object findEntityById(final Class<?> entityClass, final Object subEntityUuid) {
-        // using getReference would be more efficent, but results in very technical error messages
-        final var entity = em.find(entityClass, subEntityUuid);
+    private static <D> Field[] getDeclaredFieldsIncludingSuperClasses(final Class<D> destinationType) {
+        if (destinationType == null) {
+            return new Field[0];
+        }
+
+        return Stream.concat(
+                stream(destinationType.getDeclaredFields()),
+                stream(getDeclaredFieldsIncludingSuperClasses(destinationType.getSuperclass())))
+            .toArray(Field[]::new);
+    }
+
+    public <E> E fetchEntity(final String propertyName, final Class<E> entityClass, final Object subEntityUuid) {
+        final var entity = em.getReference(entityClass, subEntityUuid);
         if (entity != null) {
             return entity;
         }
-        throw new ValidationException("Unable to find " + DisplayName.of(entityClass) + " by uuid: " + subEntityUuid);
+        throw new ValidationException(
+                "Unable to find " + DisplayName.of(entityClass) +
+                " by " + propertyName + ": " + subEntityUuid);
     }
 
     public <S, T> T map(final S source, final Class<T> targetClass, final BiConsumer<S, T> postMapper) {
@@ -86,4 +104,13 @@ public class Mapper extends ModelMapper {
         postMapper.accept(source, target);
         return target;
     }
+
+    public <S, T> T map(final String namePrefix, final S source, final Class<T> targetClass, final BiConsumer<S, T> postMapper) {
+        if (source == null) {
+            return null;
+        }
+        final var target = map(source, targetClass);
+        postMapper.accept(source, target);
+        return target;
+    }
 }
diff --git a/src/main/java/net/hostsharing/hsadminng/mapper/MapperConfiguration.java b/src/main/java/net/hostsharing/hsadminng/mapper/MapperConfiguration.java
deleted file mode 100644
index a77b953a..00000000
--- a/src/main/java/net/hostsharing/hsadminng/mapper/MapperConfiguration.java
+++ /dev/null
@@ -1,13 +0,0 @@
-package net.hostsharing.hsadminng.mapper;
-
-import org.springframework.context.annotation.Bean;
-import org.springframework.context.annotation.Configuration;
-
-@Configuration
-public class MapperConfiguration {
-
-    @Bean
-    public Mapper modelMapper() {
-        return new Mapper();
-    }
-}
diff --git a/src/main/java/net/hostsharing/hsadminng/mapper/StandardMapper.java b/src/main/java/net/hostsharing/hsadminng/mapper/StandardMapper.java
new file mode 100644
index 00000000..42725d3d
--- /dev/null
+++ b/src/main/java/net/hostsharing/hsadminng/mapper/StandardMapper.java
@@ -0,0 +1,14 @@
+package net.hostsharing.hsadminng.mapper;
+
+import org.springframework.stereotype.Component;
+
+/**
+ * A nicer API for ModelMapper in standard mode.
+ */
+@Component
+public class StandardMapper extends Mapper {
+
+    public StandardMapper() {
+        getConfiguration().setAmbiguityIgnored(true);
+    }
+}
diff --git a/src/main/java/net/hostsharing/hsadminng/mapper/StrictMapper.java b/src/main/java/net/hostsharing/hsadminng/mapper/StrictMapper.java
new file mode 100644
index 00000000..a6d3c3fc
--- /dev/null
+++ b/src/main/java/net/hostsharing/hsadminng/mapper/StrictMapper.java
@@ -0,0 +1,19 @@
+package net.hostsharing.hsadminng.mapper;
+
+import org.springframework.stereotype.Component;
+
+import static org.modelmapper.convention.MatchingStrategies.STRICT;
+
+/**
+ * A nicer API for ModelMapper in strict mode.
+ *
+ * <p>This makes sure that resource.whateverUuid does not accidentally get mapped to entity.uuid,
+ * if resource.uuid does not exist.</p>
+ */
+@Component
+public class StrictMapper extends Mapper {
+
+    public StrictMapper() {
+        getConfiguration().setMatchingStrategy(STRICT);
+    }
+}
diff --git a/src/main/java/net/hostsharing/hsadminng/persistence/EntityExistsValidator.java b/src/main/java/net/hostsharing/hsadminng/persistence/EntityExistsValidator.java
new file mode 100644
index 00000000..fac98d33
--- /dev/null
+++ b/src/main/java/net/hostsharing/hsadminng/persistence/EntityExistsValidator.java
@@ -0,0 +1,39 @@
+package net.hostsharing.hsadminng.persistence;
+
+import net.hostsharing.hsadminng.errors.DisplayAs.DisplayName;
+import net.hostsharing.hsadminng.rbac.object.BaseEntity;
+import org.springframework.beans.factory.annotation.Autowired;
+import org.springframework.stereotype.Service;
+
+import jakarta.persistence.Entity;
+import jakarta.validation.ValidationException;
+
+@Service
+public class EntityExistsValidator {
+
+    @Autowired
+    private EntityManagerWrapper em;
+
+    public <T extends BaseEntity<T>> void validateEntityExists(final String property, final T entitySkeleton) {
+        final var foundEntity = em.find(entityClass(entitySkeleton), entitySkeleton.getUuid());
+        if ( foundEntity == null) {
+            throw new ValidationException("Unable to find " + DisplayName.of(entitySkeleton) + " by " + property + ": " + entitySkeleton.getUuid());
+        }
+    }
+
+    private static <T extends BaseEntity<T>> Class<?> entityClass(final T entityOrProxy) {
+        final var entityClass = entityClass(entityOrProxy.getClass());
+        if (entityClass == null) {
+            throw new IllegalArgumentException("@Entity not found in superclass hierarchy of " + entityOrProxy.getClass());
+        }
+        return entityClass;
+    }
+
+    private static Class<?> entityClass(final Class<?> entityOrProxyClass) {
+        return entityOrProxyClass.isAnnotationPresent(Entity.class)
+                ? entityOrProxyClass
+                : entityOrProxyClass.getSuperclass() == null
+                ? null
+                : entityClass(entityOrProxyClass.getSuperclass());
+    }
+}
diff --git a/src/main/java/net/hostsharing/hsadminng/rbac/grant/RbacGrantController.java b/src/main/java/net/hostsharing/hsadminng/rbac/grant/RbacGrantController.java
index 4ca538b9..6af53104 100644
--- a/src/main/java/net/hostsharing/hsadminng/rbac/grant/RbacGrantController.java
+++ b/src/main/java/net/hostsharing/hsadminng/rbac/grant/RbacGrantController.java
@@ -1,7 +1,7 @@
 package net.hostsharing.hsadminng.rbac.grant;
 
 import net.hostsharing.hsadminng.context.Context;
-import net.hostsharing.hsadminng.mapper.Mapper;
+import net.hostsharing.hsadminng.mapper.StandardMapper;
 import net.hostsharing.hsadminng.rbac.generated.api.v1.api.RbacGrantsApi;
 import net.hostsharing.hsadminng.rbac.generated.api.v1.model.RbacGrantResource;
 import org.springframework.beans.factory.annotation.Autowired;
@@ -22,7 +22,7 @@ public class RbacGrantController implements RbacGrantsApi {
     private Context context;
 
     @Autowired
-    private Mapper mapper;
+    private StandardMapper mapper;
 
     @Autowired
     private RbacGrantRepository rbacGrantRepository;
diff --git a/src/main/java/net/hostsharing/hsadminng/rbac/role/RbacRoleController.java b/src/main/java/net/hostsharing/hsadminng/rbac/role/RbacRoleController.java
index 5da97292..cffff888 100644
--- a/src/main/java/net/hostsharing/hsadminng/rbac/role/RbacRoleController.java
+++ b/src/main/java/net/hostsharing/hsadminng/rbac/role/RbacRoleController.java
@@ -1,7 +1,7 @@
 package net.hostsharing.hsadminng.rbac.role;
 
 import net.hostsharing.hsadminng.context.Context;
-import net.hostsharing.hsadminng.mapper.Mapper;
+import net.hostsharing.hsadminng.mapper.StandardMapper;
 import net.hostsharing.hsadminng.rbac.generated.api.v1.api.RbacRolesApi;
 import net.hostsharing.hsadminng.rbac.generated.api.v1.model.RbacRoleResource;
 import org.springframework.beans.factory.annotation.Autowired;
@@ -18,7 +18,7 @@ public class RbacRoleController implements RbacRolesApi {
     private Context context;
 
     @Autowired
-    private Mapper mapper;
+    private StandardMapper mapper;
 
     @Autowired
     private RbacRoleRepository rbacRoleRepository;
diff --git a/src/main/java/net/hostsharing/hsadminng/rbac/subject/RbacSubjectController.java b/src/main/java/net/hostsharing/hsadminng/rbac/subject/RbacSubjectController.java
index 52c0649b..1676cc7c 100644
--- a/src/main/java/net/hostsharing/hsadminng/rbac/subject/RbacSubjectController.java
+++ b/src/main/java/net/hostsharing/hsadminng/rbac/subject/RbacSubjectController.java
@@ -1,7 +1,7 @@
 package net.hostsharing.hsadminng.rbac.subject;
 
 import net.hostsharing.hsadminng.context.Context;
-import net.hostsharing.hsadminng.mapper.Mapper;
+import net.hostsharing.hsadminng.mapper.StandardMapper;
 import net.hostsharing.hsadminng.rbac.generated.api.v1.api.RbacSubjectsApi;
 import net.hostsharing.hsadminng.rbac.generated.api.v1.model.RbacSubjectPermissionResource;
 import net.hostsharing.hsadminng.rbac.generated.api.v1.model.RbacSubjectResource;
@@ -21,7 +21,7 @@ public class RbacSubjectController implements RbacSubjectsApi {
     private Context context;
 
     @Autowired
-    private Mapper mapper;
+    private StandardMapper mapper;
 
     @Autowired
     private RbacSubjectRepository rbacSubjectRepository;
diff --git a/src/main/java/net/hostsharing/hsadminng/rbac/test/cust/TestCustomerController.java b/src/main/java/net/hostsharing/hsadminng/rbac/test/cust/TestCustomerController.java
index c6bbc115..26628545 100644
--- a/src/main/java/net/hostsharing/hsadminng/rbac/test/cust/TestCustomerController.java
+++ b/src/main/java/net/hostsharing/hsadminng/rbac/test/cust/TestCustomerController.java
@@ -1,7 +1,7 @@
 package net.hostsharing.hsadminng.rbac.test.cust;
 
 import net.hostsharing.hsadminng.context.Context;
-import net.hostsharing.hsadminng.mapper.Mapper;
+import net.hostsharing.hsadminng.mapper.StandardMapper;
 import net.hostsharing.hsadminng.test.generated.api.v1.api.TestCustomersApi;
 import net.hostsharing.hsadminng.test.generated.api.v1.model.TestCustomerResource;
 import org.springframework.beans.factory.annotation.Autowired;
@@ -21,7 +21,7 @@ public class TestCustomerController implements TestCustomersApi {
     private Context context;
 
     @Autowired
-    private Mapper mapper;
+    private StandardMapper mapper;
 
     @Autowired
     private TestCustomerRepository testCustomerRepository;
diff --git a/src/main/java/net/hostsharing/hsadminng/rbac/test/pac/TestPackageController.java b/src/main/java/net/hostsharing/hsadminng/rbac/test/pac/TestPackageController.java
index c6ecc7e0..d503bf58 100644
--- a/src/main/java/net/hostsharing/hsadminng/rbac/test/pac/TestPackageController.java
+++ b/src/main/java/net/hostsharing/hsadminng/rbac/test/pac/TestPackageController.java
@@ -1,6 +1,6 @@
 package net.hostsharing.hsadminng.rbac.test.pac;
 
-import net.hostsharing.hsadminng.mapper.Mapper;
+import net.hostsharing.hsadminng.mapper.StandardMapper;
 import net.hostsharing.hsadminng.mapper.OptionalFromJson;
 import net.hostsharing.hsadminng.context.Context;
 import net.hostsharing.hsadminng.test.generated.api.v1.api.TestPackagesApi;
@@ -21,7 +21,7 @@ public class TestPackageController implements TestPackagesApi {
     private Context context;
 
     @Autowired
-    private Mapper mapper;
+    private StandardMapper mapper;
 
     @Autowired
     private TestPackageRepository testPackageRepository;
diff --git a/src/test/java/net/hostsharing/hsadminng/hs/booking/item/HsBookingItemControllerRestTest.java b/src/test/java/net/hostsharing/hsadminng/hs/booking/item/HsBookingItemControllerRestTest.java
index e28f4d38..11ecf5bc 100644
--- a/src/test/java/net/hostsharing/hsadminng/hs/booking/item/HsBookingItemControllerRestTest.java
+++ b/src/test/java/net/hostsharing/hsadminng/hs/booking/item/HsBookingItemControllerRestTest.java
@@ -1,17 +1,20 @@
 package net.hostsharing.hsadminng.hs.booking.item;
 
+import net.hostsharing.hsadminng.config.JsonObjectMapperConfiguration;
 import net.hostsharing.hsadminng.context.Context;
 import net.hostsharing.hsadminng.hs.booking.project.HsBookingProjectRealEntity;
 import net.hostsharing.hsadminng.hs.booking.project.HsBookingProjectRealRepository;
-import net.hostsharing.hsadminng.mapper.Mapper;
+import net.hostsharing.hsadminng.mapper.StrictMapper;
+import net.hostsharing.hsadminng.persistence.EntityManagerWrapper;
 import org.junit.jupiter.api.BeforeEach;
 import org.junit.jupiter.api.Nested;
 import org.junit.jupiter.api.Test;
 import org.junit.runner.RunWith;
-import org.mockito.Mock;
 import org.springframework.beans.factory.annotation.Autowired;
 import org.springframework.boot.test.autoconfigure.web.servlet.WebMvcTest;
+import org.springframework.boot.test.context.TestConfiguration;
 import org.springframework.boot.test.mock.mockito.MockBean;
+import org.springframework.context.annotation.Bean;
 import org.springframework.context.annotation.Import;
 import org.springframework.http.MediaType;
 import org.springframework.test.context.junit4.SpringRunner;
@@ -28,13 +31,14 @@ import java.util.UUID;
 import static net.hostsharing.hsadminng.rbac.test.JsonMatcher.lenientlyEquals;
 import static org.hamcrest.Matchers.matchesRegex;
 import static org.mockito.ArgumentMatchers.any;
+import static org.mockito.Mockito.mock;
 import static org.mockito.Mockito.when;
 import static org.springframework.test.web.servlet.result.MockMvcResultMatchers.header;
 import static org.springframework.test.web.servlet.result.MockMvcResultMatchers.jsonPath;
 import static org.springframework.test.web.servlet.result.MockMvcResultMatchers.status;
 
 @WebMvcTest(HsBookingItemController.class)
-@Import(Mapper.class)
+@Import({StrictMapper.class, JsonObjectMapperConfiguration.class})
 @RunWith(SpringRunner.class)
 class HsBookingItemControllerRestTest {
 
@@ -44,8 +48,12 @@ class HsBookingItemControllerRestTest {
     @MockBean
     Context contextMock;
 
-    @Mock
-    EntityManager em;
+    @Autowired
+    @SuppressWarnings("unused") // not used in test, but in controller class
+    StrictMapper mapper;
+
+    @MockBean
+    EntityManagerWrapper em;
 
     @MockBean
     EntityManagerFactory emf;
@@ -56,6 +64,16 @@ class HsBookingItemControllerRestTest {
     @MockBean
     HsBookingItemRbacRepository rbacBookingItemRepo;
 
+    @TestConfiguration
+    public static class TestConfig {
+
+        @Bean
+        public EntityManager entityManager() {
+            return mock(EntityManager.class);
+        }
+
+    }
+
     @BeforeEach
     void init() {
         when(emf.createEntityManager()).thenReturn(em);
diff --git a/src/test/java/net/hostsharing/hsadminng/hs/booking/item/validators/HsDomainSetupBookingItemValidatorUnitTest.java b/src/test/java/net/hostsharing/hsadminng/hs/booking/item/validators/HsDomainSetupBookingItemValidatorUnitTest.java
index 60356401..52a63509 100644
--- a/src/test/java/net/hostsharing/hsadminng/hs/booking/item/validators/HsDomainSetupBookingItemValidatorUnitTest.java
+++ b/src/test/java/net/hostsharing/hsadminng/hs/booking/item/validators/HsDomainSetupBookingItemValidatorUnitTest.java
@@ -35,7 +35,8 @@ class HsDomainSetupBookingItemValidatorUnitTest {
                 .project(project)
                 .caption("Test-Domain")
                 .resources(Map.ofEntries(
-                        entry("domainName", "example.org")
+                        entry("domainName", "example.org"),
+                        entry("targetUnixUser", "xyz00")
                 ))
                 .build();
 
@@ -55,6 +56,7 @@ class HsDomainSetupBookingItemValidatorUnitTest {
                 .caption("Test-Domain")
                 .resources(Map.ofEntries(
                         entry("domainName", "example.org"),
+                        entry("targetUnixUser", "xyz00"),
                         entry("verificationCode", "1234-5678-9100")
                 ))
                 .build();
@@ -73,7 +75,8 @@ class HsDomainSetupBookingItemValidatorUnitTest {
                 .project(project)
                 .caption("Test-Domain")
                 .resources(Map.ofEntries(
-                        entry("domainName", right(TOO_LONG_DOMAIN_NAME, 253))
+                        entry("domainName", right(TOO_LONG_DOMAIN_NAME, 253)),
+                        entry("targetUnixUser", "xyz00")
                 ))
                 .build();
 
@@ -91,7 +94,8 @@ class HsDomainSetupBookingItemValidatorUnitTest {
                 .project(project)
                 .caption("Test-Domain")
                 .resources(Map.ofEntries(
-                        entry("domainName", right(TOO_LONG_DOMAIN_NAME, 254))
+                        entry("domainName", right(TOO_LONG_DOMAIN_NAME, 254)),
+                        entry("targetUnixUser", "xyz00")
                 ))
                 .build();
 
@@ -102,6 +106,44 @@ class HsDomainSetupBookingItemValidatorUnitTest {
         assertThat(result).contains("'D-12345:Test-Project:Test-Domain.resources.domainName' length is expected to be at max 253 but length of 'dfghijklmnopqrstuvwxyz0123456789.asdfghijklmnopqrstuvwxyz0123456789.asdfghijklmnopqrstuvwxyz0123456789.asdfghijklmnopqrstuvwxyz0123456789.asdfghijklmnopqrstuvwxyz0123456789.asdfghijklmnopqrstuvwxyz0123456789.asdfghijklmnopqrstuvwxyz0123456789.example.org' is 254");
     }
 
+    @Test
+    void acceptsValidUnixUser() {
+        final var domainSetupBookingItemEntity = HsBookingItemRealEntity.builder()
+                .type(DOMAIN_SETUP)
+                .project(project)
+                .caption("Test-Domain")
+                .resources(Map.ofEntries(
+                        entry("domainName", "example.com"),
+                        entry("targetUnixUser", "xyz00-test")
+                ))
+                .build();
+
+        // when
+        final var result = HsBookingItemEntityValidatorRegistry.doValidate(em, domainSetupBookingItemEntity);
+
+        // then
+        assertThat(result).isEmpty();
+    }
+
+    @Test
+    void rejectsInvalidUnixUser() {
+        final var domainSetupBookingItemEntity = HsBookingItemRealEntity.builder()
+                .type(DOMAIN_SETUP)
+                .project(project)
+                .caption("Test-Domain")
+                .resources(Map.ofEntries(
+                        entry("domainName", "example.com"),
+                        entry("targetUnixUser", "xyz00test")
+                ))
+                .build();
+
+        // when
+        final var result = HsBookingItemEntityValidatorRegistry.doValidate(em, domainSetupBookingItemEntity);
+
+        // then
+        assertThat(result).contains("'D-12345:Test-Project:Test-Domain.resources.targetUnixUser' = 'xyz00test' is not a valid unix-user name");
+    }
+
     @ParameterizedTest
     @ValueSource(strings = {
             "de", "com", "net", "org", "actually-any-top-level-domain",
@@ -123,7 +165,8 @@ class HsDomainSetupBookingItemValidatorUnitTest {
                 .project(project)
                 .caption("Test-Domain")
                 .resources(Map.ofEntries(
-                        entry("domainName", secondLevelRegistrarDomain)
+                        entry("domainName", secondLevelRegistrarDomain),
+                        entry("targetUnixUser", "xyz00")
                 ))
                 .build();
 
@@ -148,7 +191,8 @@ class HsDomainSetupBookingItemValidatorUnitTest {
                 .project(project)
                 .caption("Test-Domain")
                 .resources(Map.ofEntries(
-                        entry("domainName", secondLevelRegistrarDomain)
+                        entry("domainName", secondLevelRegistrarDomain),
+                        entry("targetUnixUser", "xyz00")
                 ))
                 .build();
 
@@ -170,6 +214,7 @@ class HsDomainSetupBookingItemValidatorUnitTest {
         // then
         assertThat(validator.properties()).map(Map::toString).containsExactlyInAnyOrder(
                 "{type=string, propertyName=domainName, matchesRegEx=[^((?!-)[A-Za-z0-9-]{1,63}(?<!-)\\.)+[A-Za-z]{2,12}], matchesRegExDescription=is not a (non-top-level) fully qualified domain name, notMatchesRegEx=[[^.]+, (co|org|gov|ac|sch)\\.uk, (com|net|org|edu|gov|asn|id)\\.au, (co|ne|or|ac|go)\\.jp, (com|net|org|gov|edu|ac)\\.cn, (com|net|org|gov|edu|mil|art)\\.br, (co|net|org|gen|firm|ind)\\.in, (com|net|org|gob|edu)\\.mx, (gov|edu)\\.it, (co|net|org|govt|ac|school|geek|kiwi)\\.nz, (co|ne|or|go|re|pe)\\.kr], notMatchesRegExDescription=is a forbidden registrar-level domain name, maxLength=253, required=true, writeOnce=true}",
+                "{type=string, propertyName=targetUnixUser, matchesRegEx=[^[a-z][a-z0-9]{2}[0-9]{2}$|^[a-z][a-z0-9]{2}[0-9]{2}-[a-z0-9\\._-]+$], matchesRegExDescription=is not a valid unix-user name, maxLength=253, required=true, writeOnce=true}",
                 "{type=string, propertyName=verificationCode, minLength=12, maxLength=64, computed=IN_INIT}");
     }
 }
diff --git a/src/test/java/net/hostsharing/hsadminng/hs/hosting/asset/HsHostingAssetControllerRestTest.java b/src/test/java/net/hostsharing/hsadminng/hs/hosting/asset/HsHostingAssetControllerRestTest.java
index 0d9dd87b..9dc5741b 100644
--- a/src/test/java/net/hostsharing/hsadminng/hs/hosting/asset/HsHostingAssetControllerRestTest.java
+++ b/src/test/java/net/hostsharing/hsadminng/hs/hosting/asset/HsHostingAssetControllerRestTest.java
@@ -9,7 +9,7 @@ import net.hostsharing.hsadminng.config.JsonObjectMapperConfiguration;
 import net.hostsharing.hsadminng.context.Context;
 import net.hostsharing.hsadminng.hs.booking.item.HsBookingItemRealRepository;
 import net.hostsharing.hsadminng.mapper.Array;
-import net.hostsharing.hsadminng.mapper.Mapper;
+import net.hostsharing.hsadminng.mapper.StandardMapper;
 import net.hostsharing.hsadminng.persistence.EntityManagerWrapper;
 import org.junit.jupiter.api.BeforeEach;
 import org.junit.jupiter.api.Test;
@@ -52,7 +52,7 @@ import static org.springframework.test.web.servlet.result.MockMvcResultMatchers.
 import static org.springframework.test.web.servlet.result.MockMvcResultMatchers.status;
 
 @WebMvcTest(HsHostingAssetController.class)
-@Import({Mapper.class, JsonObjectMapperConfiguration.class})
+@Import({ StandardMapper.class, JsonObjectMapperConfiguration.class})
 @RunWith(SpringRunner.class)
 public class HsHostingAssetControllerRestTest {
 
@@ -63,10 +63,11 @@ public class HsHostingAssetControllerRestTest {
     Context contextMock;
 
     @Autowired
-    Mapper mapper;
+    @SuppressWarnings("unused") // not used in test, but in controller class
+    StandardMapper mapper;
 
     @MockBean
-    private EntityManagerWrapper em;
+    EntityManagerWrapper em;
 
     @MockBean
     EntityManagerFactory emf;
@@ -90,6 +91,7 @@ public class HsHostingAssetControllerRestTest {
         }
 
     }
+
     enum ListTestCases {
         CLOUD_SERVER(
                 List.of(
diff --git a/src/test/java/net/hostsharing/hsadminng/hs/hosting/asset/validators/HsDomainSetupHostingAssetValidatorUnitTest.java b/src/test/java/net/hostsharing/hsadminng/hs/hosting/asset/validators/HsDomainSetupHostingAssetValidatorUnitTest.java
index 8acca8d9..e5a119d5 100644
--- a/src/test/java/net/hostsharing/hsadminng/hs/hosting/asset/validators/HsDomainSetupHostingAssetValidatorUnitTest.java
+++ b/src/test/java/net/hostsharing/hsadminng/hs/hosting/asset/validators/HsDomainSetupHostingAssetValidatorUnitTest.java
@@ -42,7 +42,8 @@ class HsDomainSetupHostingAssetValidatorUnitTest {
                         .project(project)
                         .type(HsBookingItemType.DOMAIN_SETUP)
                         .resources(new HashMap<>(ofEntries(
-                                entry("domainName", domainName)
+                                entry("domainName", domainName),
+                                entry("targetUnixUser", "xyz00")
                         ))));
         HsBookingItemEntityValidatorRegistry.forType(HsBookingItemType.DOMAIN_SETUP).prepareProperties(null, bookingItem);
         return HsHostingAssetRbacEntity.builder()
diff --git a/src/test/java/net/hostsharing/hsadminng/hs/migration/ImportHostingAssets.java b/src/test/java/net/hostsharing/hsadminng/hs/migration/ImportHostingAssets.java
index 9d73ac89..634ba207 100644
--- a/src/test/java/net/hostsharing/hsadminng/hs/migration/ImportHostingAssets.java
+++ b/src/test/java/net/hostsharing/hsadminng/hs/migration/ImportHostingAssets.java
@@ -1680,13 +1680,19 @@ public class ImportHostingAssets extends BaseOfficeDataImport {
                 final var relatedProject = domainSetup.getSubHostingAssets().stream()
                         .map(ha -> ha.getAssignedToAsset() != null ? ha.getAssignedToAsset().getRelatedProject() : null)
                         .findAny().orElseThrow();
+                final var targetUnixUser = domainSetup.getSubHostingAssets().stream()
+                        .filter(subAsset -> subAsset.getType() == DOMAIN_HTTP_SETUP)
+                        .map(domainHttpSetup -> domainHttpSetup.getAssignedToAsset().getIdentifier())
+                        .findAny().orElse(null);
                 final var bookingItem = HsBookingItemRealEntity.builder()
                         .type(HsBookingItemType.DOMAIN_SETUP)
                         .caption("BI " + domainSetup.getIdentifier())
                         .project((HsBookingProjectRealEntity) relatedProject)
                         //.validity(toPostgresDateRange(created, cancelled))
                         .resources(Map.ofEntries(
-                                entry("domainName", domainSetup.getIdentifier())))
+                                entry("domainName", domainSetup.getIdentifier()),
+                                entry("targetUnixUser", targetUnixUser)
+                        ))
                         .build();
                 domainSetup.setBookingItem(bookingItem);
                 bookingItems.put(nextAvailableBookingItemId(), bookingItem);
diff --git a/src/test/java/net/hostsharing/hsadminng/hs/office/bankaccount/HsOfficeBankAccountControllerRestTest.java b/src/test/java/net/hostsharing/hsadminng/hs/office/bankaccount/HsOfficeBankAccountControllerRestTest.java
index 6dcd1cb5..624e9994 100644
--- a/src/test/java/net/hostsharing/hsadminng/hs/office/bankaccount/HsOfficeBankAccountControllerRestTest.java
+++ b/src/test/java/net/hostsharing/hsadminng/hs/office/bankaccount/HsOfficeBankAccountControllerRestTest.java
@@ -1,7 +1,7 @@
 package net.hostsharing.hsadminng.hs.office.bankaccount;
 
 import net.hostsharing.hsadminng.context.Context;
-import net.hostsharing.hsadminng.mapper.Mapper;
+import net.hostsharing.hsadminng.mapper.StandardMapper;
 import org.junit.jupiter.params.ParameterizedTest;
 import org.junit.jupiter.params.provider.EnumSource;
 import org.springframework.beans.factory.annotation.Autowired;
@@ -25,7 +25,7 @@ class HsOfficeBankAccountControllerRestTest {
     Context contextMock;
 
     @MockBean
-    Mapper mapper;
+    StandardMapper mapper;
 
     @MockBean
     HsOfficeBankAccountRepository bankAccountRepo;
diff --git a/src/test/java/net/hostsharing/hsadminng/hs/office/coopassets/HsOfficeCoopAssetsTransactionControllerRestTest.java b/src/test/java/net/hostsharing/hsadminng/hs/office/coopassets/HsOfficeCoopAssetsTransactionControllerRestTest.java
index 0e4716d4..03a1c71b 100644
--- a/src/test/java/net/hostsharing/hsadminng/hs/office/coopassets/HsOfficeCoopAssetsTransactionControllerRestTest.java
+++ b/src/test/java/net/hostsharing/hsadminng/hs/office/coopassets/HsOfficeCoopAssetsTransactionControllerRestTest.java
@@ -1,7 +1,7 @@
 package net.hostsharing.hsadminng.hs.office.coopassets;
 
 import net.hostsharing.hsadminng.context.Context;
-import net.hostsharing.hsadminng.mapper.Mapper;
+import net.hostsharing.hsadminng.mapper.StandardMapper;
 import net.hostsharing.hsadminng.rbac.test.JsonBuilder;
 import org.junit.jupiter.params.ParameterizedTest;
 import org.junit.jupiter.params.provider.EnumSource;
@@ -30,7 +30,7 @@ class HsOfficeCoopAssetsTransactionControllerRestTest {
     Context contextMock;
 
     @MockBean
-    Mapper mapper;
+    StandardMapper mapper;
 
     @MockBean
     HsOfficeCoopAssetsTransactionRepository coopAssetsTransactionRepo;
diff --git a/src/test/java/net/hostsharing/hsadminng/hs/office/coopshares/HsOfficeCoopSharesTransactionControllerRestTest.java b/src/test/java/net/hostsharing/hsadminng/hs/office/coopshares/HsOfficeCoopSharesTransactionControllerRestTest.java
index 4d44c0fb..1e33fde9 100644
--- a/src/test/java/net/hostsharing/hsadminng/hs/office/coopshares/HsOfficeCoopSharesTransactionControllerRestTest.java
+++ b/src/test/java/net/hostsharing/hsadminng/hs/office/coopshares/HsOfficeCoopSharesTransactionControllerRestTest.java
@@ -1,7 +1,7 @@
 package net.hostsharing.hsadminng.hs.office.coopshares;
 
 import net.hostsharing.hsadminng.context.Context;
-import net.hostsharing.hsadminng.mapper.Mapper;
+import net.hostsharing.hsadminng.mapper.StandardMapper;
 import net.hostsharing.hsadminng.rbac.test.JsonBuilder;
 import org.junit.jupiter.params.ParameterizedTest;
 import org.junit.jupiter.params.provider.EnumSource;
@@ -30,7 +30,7 @@ class HsOfficeCoopSharesTransactionControllerRestTest {
     Context contextMock;
 
     @MockBean
-    Mapper mapper;
+    StandardMapper mapper;
 
     @MockBean
     HsOfficeCoopSharesTransactionRepository coopSharesTransactionRepo;
diff --git a/src/test/java/net/hostsharing/hsadminng/hs/office/debitor/HsOfficeDebitorControllerAcceptanceTest.java b/src/test/java/net/hostsharing/hsadminng/hs/office/debitor/HsOfficeDebitorControllerAcceptanceTest.java
index 98ba650c..d0954b6a 100644
--- a/src/test/java/net/hostsharing/hsadminng/hs/office/debitor/HsOfficeDebitorControllerAcceptanceTest.java
+++ b/src/test/java/net/hostsharing/hsadminng/hs/office/debitor/HsOfficeDebitorControllerAcceptanceTest.java
@@ -433,7 +433,7 @@ class HsOfficeDebitorControllerAcceptanceTest extends ContextBasedTestWithCleanu
                     .post("http://localhost/api/hs/office/debitors")
                 .then().log().all().assertThat()
                     .statusCode(400)
-                    .body("message", is("ERROR: [400] Unable to find RealRelation by uuid: 00000000-0000-0000-0000-000000000000"));
+                    .body("message", is("ERROR: [400] Unable to find RealRelation by debitorRelUuid: 00000000-0000-0000-0000-000000000000"));
                 // @formatter:on
         }
     }
diff --git a/src/test/java/net/hostsharing/hsadminng/hs/office/membership/HsOfficeMembershipControllerRestTest.java b/src/test/java/net/hostsharing/hsadminng/hs/office/membership/HsOfficeMembershipControllerRestTest.java
index 2a5005e6..64de089c 100644
--- a/src/test/java/net/hostsharing/hsadminng/hs/office/membership/HsOfficeMembershipControllerRestTest.java
+++ b/src/test/java/net/hostsharing/hsadminng/hs/office/membership/HsOfficeMembershipControllerRestTest.java
@@ -3,7 +3,7 @@ package net.hostsharing.hsadminng.hs.office.membership;
 import net.hostsharing.hsadminng.context.Context;
 import net.hostsharing.hsadminng.hs.office.coopassets.HsOfficeCoopAssetsTransactionRepository;
 import net.hostsharing.hsadminng.hs.office.partner.HsOfficePartnerEntity;
-import net.hostsharing.hsadminng.mapper.Mapper;
+import net.hostsharing.hsadminng.mapper.StandardMapper;
 import org.junit.jupiter.api.BeforeEach;
 import org.junit.jupiter.api.Nested;
 import org.junit.jupiter.api.Test;
@@ -32,7 +32,7 @@ import static org.springframework.test.web.servlet.result.MockMvcResultMatchers.
 import static org.springframework.test.web.servlet.result.MockMvcResultMatchers.status;
 
 @WebMvcTest(HsOfficeMembershipController.class)
-@Import(Mapper.class)
+@Import(StandardMapper.class)
 public class HsOfficeMembershipControllerRestTest {
 
     @Autowired
@@ -115,7 +115,7 @@ public class HsOfficeMembershipControllerRestTest {
                     .andExpect(status().is4xxClientError())
                     .andExpect(jsonPath("statusCode", is(400)))
                     .andExpect(jsonPath("statusPhrase", is("Bad Request")))
-                    .andExpect(jsonPath("message", is("ERROR: [400] Unable to find Partner by uuid: " + givenPartnerUuid)));
+                    .andExpect(jsonPath("message", is("ERROR: [400] Unable to find Partner by partner.uuid: " + givenPartnerUuid)));
         }
 
         @ParameterizedTest
diff --git a/src/test/java/net/hostsharing/hsadminng/hs/office/membership/HsOfficeMembershipEntityPatcherUnitTest.java b/src/test/java/net/hostsharing/hsadminng/hs/office/membership/HsOfficeMembershipEntityPatcherUnitTest.java
index 2e739e7f..841e7e12 100644
--- a/src/test/java/net/hostsharing/hsadminng/hs/office/membership/HsOfficeMembershipEntityPatcherUnitTest.java
+++ b/src/test/java/net/hostsharing/hsadminng/hs/office/membership/HsOfficeMembershipEntityPatcherUnitTest.java
@@ -4,7 +4,7 @@ import io.hypersistence.utils.hibernate.type.range.Range;
 import net.hostsharing.hsadminng.hs.office.debitor.HsOfficeDebitorEntity;
 import net.hostsharing.hsadminng.hs.office.generated.api.v1.model.HsOfficeMembershipPatchResource;
 import net.hostsharing.hsadminng.hs.office.generated.api.v1.model.HsOfficeMembershipStatusResource;
-import net.hostsharing.hsadminng.mapper.Mapper;
+import net.hostsharing.hsadminng.mapper.StandardMapper;
 import net.hostsharing.hsadminng.rbac.test.PatchUnitTestBase;
 import org.junit.jupiter.api.BeforeEach;
 import org.junit.jupiter.api.TestInstance;
@@ -40,7 +40,7 @@ class HsOfficeMembershipEntityPatcherUnitTest extends PatchUnitTestBase<
     @Mock
     private EntityManager em;
 
-    private Mapper mapper = new Mapper();
+    private StandardMapper mapper = new StandardMapper();
 
     @BeforeEach
     void initMocks() {
diff --git a/src/test/java/net/hostsharing/hsadminng/hs/office/partner/HsOfficePartnerControllerRestTest.java b/src/test/java/net/hostsharing/hsadminng/hs/office/partner/HsOfficePartnerControllerRestTest.java
index a42a4780..2af222dc 100644
--- a/src/test/java/net/hostsharing/hsadminng/hs/office/partner/HsOfficePartnerControllerRestTest.java
+++ b/src/test/java/net/hostsharing/hsadminng/hs/office/partner/HsOfficePartnerControllerRestTest.java
@@ -5,7 +5,7 @@ import net.hostsharing.hsadminng.hs.office.contact.HsOfficeContactRbacEntity;
 import net.hostsharing.hsadminng.hs.office.person.HsOfficePersonEntity;
 import net.hostsharing.hsadminng.hs.office.relation.HsOfficeRelationRealEntity;
 import net.hostsharing.hsadminng.hs.office.relation.HsOfficeRelationRealRepository;
-import net.hostsharing.hsadminng.mapper.Mapper;
+import net.hostsharing.hsadminng.mapper.StandardMapper;
 import org.junit.jupiter.api.BeforeEach;
 import org.junit.jupiter.api.Nested;
 import org.junit.jupiter.api.Test;
@@ -36,7 +36,7 @@ import static org.springframework.test.web.servlet.result.MockMvcResultMatchers.
 import static org.springframework.test.web.servlet.result.MockMvcResultMatchers.status;
 
 @WebMvcTest(HsOfficePartnerController.class)
-@Import(Mapper.class)
+@Import(StandardMapper.class)
 class HsOfficePartnerControllerRestTest {
 
     static final UUID GIVEN_MANDANTE_UUID = UUID.randomUUID();
diff --git a/src/test/java/net/hostsharing/hsadminng/hs/office/sepamandate/HsOfficeSepaMandateControllerAcceptanceTest.java b/src/test/java/net/hostsharing/hsadminng/hs/office/sepamandate/HsOfficeSepaMandateControllerAcceptanceTest.java
index 026ce95c..89b25f35 100644
--- a/src/test/java/net/hostsharing/hsadminng/hs/office/sepamandate/HsOfficeSepaMandateControllerAcceptanceTest.java
+++ b/src/test/java/net/hostsharing/hsadminng/hs/office/sepamandate/HsOfficeSepaMandateControllerAcceptanceTest.java
@@ -195,7 +195,7 @@ class HsOfficeSepaMandateControllerAcceptanceTest extends ContextBasedTestWithCl
                     .post("http://localhost/api/hs/office/sepamandates")
                 .then().log().all().assertThat()
                     .statusCode(400)
-                    .body("message", is("ERROR: [400] Unable to find BankAccount by uuid: 00000000-0000-0000-0000-000000000000"));
+                    .body("message", is("ERROR: [400] Unable to find BankAccount with uuid 00000000-0000-0000-0000-000000000000"));
             // @formatter:on
         }
 
@@ -225,7 +225,7 @@ class HsOfficeSepaMandateControllerAcceptanceTest extends ContextBasedTestWithCl
                     .post("http://localhost/api/hs/office/sepamandates")
                 .then().log().all().assertThat()
                     .statusCode(400)
-                    .body("message", is("ERROR: [400] Unable to find Debitor by uuid: 00000000-0000-0000-0000-000000000000"));
+                    .body("message", is("ERROR: [400] Unable to find Debitor with uuid 00000000-0000-0000-0000-000000000000"));
                 // @formatter:on
         }
     }
diff --git a/src/test/java/net/hostsharing/hsadminng/rbac/context/ContextIntegrationTests.java b/src/test/java/net/hostsharing/hsadminng/rbac/context/ContextIntegrationTests.java
index c48f782e..cf5f387e 100644
--- a/src/test/java/net/hostsharing/hsadminng/rbac/context/ContextIntegrationTests.java
+++ b/src/test/java/net/hostsharing/hsadminng/rbac/context/ContextIntegrationTests.java
@@ -1,7 +1,7 @@
 package net.hostsharing.hsadminng.rbac.context;
 
 import net.hostsharing.hsadminng.context.Context;
-import net.hostsharing.hsadminng.mapper.Mapper;
+import net.hostsharing.hsadminng.mapper.StandardMapper;
 import net.hostsharing.hsadminng.mapper.Array;
 import net.hostsharing.hsadminng.rbac.test.JpaAttempt;
 import org.junit.jupiter.api.Test;
@@ -17,7 +17,7 @@ import jakarta.servlet.http.HttpServletRequest;
 import static org.assertj.core.api.Assertions.assertThat;
 
 @DataJpaTest
-@ComponentScan(basePackageClasses = { Context.class, JpaAttempt.class, Mapper.class })
+@ComponentScan(basePackageClasses = { Context.class, JpaAttempt.class, StandardMapper.class })
 @DirtiesContext
 class ContextIntegrationTests {
 
diff --git a/src/test/java/net/hostsharing/hsadminng/rbac/role/RbacRoleControllerRestTest.java b/src/test/java/net/hostsharing/hsadminng/rbac/role/RbacRoleControllerRestTest.java
index 2d3d74c7..7d38b0e9 100644
--- a/src/test/java/net/hostsharing/hsadminng/rbac/role/RbacRoleControllerRestTest.java
+++ b/src/test/java/net/hostsharing/hsadminng/rbac/role/RbacRoleControllerRestTest.java
@@ -1,7 +1,7 @@
 package net.hostsharing.hsadminng.rbac.role;
 
 import net.hostsharing.hsadminng.context.Context;
-import net.hostsharing.hsadminng.mapper.Mapper;
+import net.hostsharing.hsadminng.mapper.StandardMapper;
 import org.junit.jupiter.api.BeforeEach;
 import org.junit.jupiter.api.Test;
 import org.junit.runner.RunWith;
@@ -30,7 +30,7 @@ import static org.springframework.test.web.servlet.result.MockMvcResultMatchers.
 import static org.springframework.test.web.servlet.result.MockMvcResultMatchers.status;
 
 @WebMvcTest(RbacRoleController.class)
-@Import(Mapper.class)
+@Import(StandardMapper.class)
 @RunWith(SpringRunner.class)
 class RbacRoleControllerRestTest {
 
diff --git a/src/test/java/net/hostsharing/hsadminng/rbac/subject/RbacSubjectControllerRestTest.java b/src/test/java/net/hostsharing/hsadminng/rbac/subject/RbacSubjectControllerRestTest.java
index d23a8394..2131c7d9 100644
--- a/src/test/java/net/hostsharing/hsadminng/rbac/subject/RbacSubjectControllerRestTest.java
+++ b/src/test/java/net/hostsharing/hsadminng/rbac/subject/RbacSubjectControllerRestTest.java
@@ -1,7 +1,7 @@
 package net.hostsharing.hsadminng.rbac.subject;
 
 import net.hostsharing.hsadminng.context.Context;
-import net.hostsharing.hsadminng.mapper.Mapper;
+import net.hostsharing.hsadminng.mapper.StandardMapper;
 import org.junit.jupiter.api.BeforeEach;
 import org.junit.jupiter.api.Test;
 import org.junit.runner.RunWith;
@@ -31,7 +31,7 @@ import static org.springframework.test.web.servlet.result.MockMvcResultMatchers.
 import static org.springframework.test.web.servlet.result.MockMvcResultMatchers.status;
 
 @WebMvcTest(RbacSubjectController.class)
-@Import(Mapper.class)
+@Import(StandardMapper.class)
 @RunWith(SpringRunner.class)
 class RbacSubjectControllerRestTest {
 
diff --git a/src/test/java/net/hostsharing/hsadminng/rbac/test/MapperUnitTest.java b/src/test/java/net/hostsharing/hsadminng/rbac/test/MapperUnitTest.java
index 0e01cd05..b90c7cb1 100644
--- a/src/test/java/net/hostsharing/hsadminng/rbac/test/MapperUnitTest.java
+++ b/src/test/java/net/hostsharing/hsadminng/rbac/test/MapperUnitTest.java
@@ -2,7 +2,7 @@ package net.hostsharing.hsadminng.rbac.test;
 
 import lombok.*;
 import net.hostsharing.hsadminng.errors.DisplayAs;
-import net.hostsharing.hsadminng.mapper.Mapper;
+import net.hostsharing.hsadminng.mapper.StandardMapper;
 import org.junit.jupiter.api.Test;
 import org.junit.jupiter.api.extension.ExtendWith;
 import org.mockito.InjectMocks;
@@ -27,7 +27,7 @@ class MapperUnitTest {
     EntityManager em;
 
     @InjectMocks
-    Mapper mapper;
+    StandardMapper mapper;
 
     final UUID GIVEN_UUID = UUID.randomUUID();
 
@@ -50,7 +50,7 @@ class MapperUnitTest {
     @Test
     void mapsBeanWithExistingSubEntity() {
         final SourceBean givenSource = SourceBean.builder().a("1234").b("Text").s1(new SubSourceBean1(GIVEN_UUID)).build();
-        when(em.find(SubTargetBean1.class, GIVEN_UUID)).thenReturn(new SubTargetBean1(GIVEN_UUID, "xxx"));
+        when(em.getReference(SubTargetBean1.class, GIVEN_UUID)).thenReturn(new SubTargetBean1(GIVEN_UUID, "xxx"));
 
         final var result = mapper.map(givenSource, TargetBean.class);
         assertThat(result).usingRecursiveComparison().isEqualTo(
@@ -81,27 +81,27 @@ class MapperUnitTest {
     @Test
     void mapsBeanWithSubEntityNotFound() {
         final SourceBean givenSource = SourceBean.builder().a("1234").b("Text").s1(new SubSourceBean1(GIVEN_UUID)).build();
-        when(em.find(SubTargetBean1.class, GIVEN_UUID)).thenReturn(null);
+        when(em.getReference(SubTargetBean1.class, GIVEN_UUID)).thenReturn(null);
 
         final var exception = catchThrowable(() ->
                 mapper.map(givenSource, TargetBean.class)
         );
 
         assertThat(exception).isInstanceOf(ValidationException.class)
-                .hasMessage("Unable to find SubTargetBean1 by uuid: " + GIVEN_UUID);
+                .hasMessage("Unable to find SubTargetBean1 by s1.uuid: " + GIVEN_UUID);
     }
 
     @Test
     void mapsBeanWithSubEntityNotFoundAndDisplayName() {
         final SourceBean givenSource = SourceBean.builder().a("1234").b("Text").s2(new SubSourceBean2(GIVEN_UUID)).build();
-        when(em.find(SubTargetBean2.class, GIVEN_UUID)).thenReturn(null);
+        when(em.getReference(SubTargetBean2.class, GIVEN_UUID)).thenReturn(null);
 
         final var exception = catchThrowable(() ->
                 mapper.map(givenSource, TargetBean.class)
         );
 
         assertThat(exception).isInstanceOf(ValidationException.class)
-                .hasMessage("Unable to find SomeDisplayName by uuid: " + GIVEN_UUID);
+                .hasMessage("Unable to find SomeDisplayName by s2.uuid: " + GIVEN_UUID);
     }
 
     @Test