src/main/java/net/hostsharing/hsadminng/errors/Validate.java

@@ -0,0 +1,23 @@
+package net.hostsharing.hsadminng.errors;
+
+import lombok.AllArgsConstructor;
+
+import jakarta.validation.ValidationException;
+
+@AllArgsConstructor
+public class Validate {
+
+    final String variableNames;
+
+    public static Validate validate(final String variableNames) {
+        return new Validate(variableNames);
+    }
+
+    public final void atMaxOneNonNull(final Object var1, final Object var2) {
+        if (var1 != null && var2 != null) {
+            throw new ValidationException(
+                    "Exactly one of (" + variableNames + ") must be non-null, " +
+                            "but are (" + var1 + ", " + var2 + ")");
+        }
+    }
+}

src/main/java/net/hostsharing/hsadminng/hs/office/coopassets/HsOfficeCoopAssetsTransactionController.java

@@ -290,11 +290,10 @@ public class HsOfficeCoopAssetsTransactionController implements HsOfficeCoopAsse
         if (adoptingMembershipMemberNumber != null) {
             final var adoptingMemberNumber = Integer.valueOf(adoptingMembershipMemberNumber.substring("M-".length()));
             final var adoptingMembership = membershipRepo.findMembershipByMemberNumber(adoptingMemberNumber);
-            if (adoptingMembership != null) {
+            return adoptingMembership.orElseThrow( () ->
-                return adoptingMembership;
+                    new ValidationException("adoptingMembership.memberNumber='" + adoptingMembershipMemberNumber
-            }
+                            + "' not found or not accessible")
-            throw new ValidationException("adoptingMembership.memberNumber='" + adoptingMembershipMemberNumber
+            );
-                    + "' not found or not accessible");
         }
 
         throw new ValidationException(

src/main/java/net/hostsharing/hsadminng/hs/office/debitor/HsOfficeDebitorController.java

@@ -57,12 +57,15 @@ public class HsOfficeDebitorController implements HsOfficeDebitorsApi {
             final String currentSubject,
             final String assumedRoles,
             final String name,
-            final String debitorNumber) {
+            final UUID partnerUuid,
+            final String partnerNumber) {
         context.define(currentSubject, assumedRoles);
 
-        final var entities = debitorNumber != null
+        final var entities = partnerNumber != null
-                ? debitorRepo.findDebitorByDebitorNumber(cropTag("D-", debitorNumber))
+                ? debitorRepo.findDebitorsByPartnerNumber(cropTag("P-", partnerNumber))
-                : debitorRepo.findDebitorByOptionalNameLike(name);
+                    : partnerUuid != null
+                        ? debitorRepo.findDebitorsByPartnerUuid(partnerUuid)
+                        : debitorRepo.findDebitorsByOptionalNameLike(name);
 
         final var resources = mapper.mapList(entities, HsOfficeDebitorResource.class, ENTITY_TO_RESOURCE_POSTMAPPER);
         return ResponseEntity.ok(resources);
@@ -133,6 +136,23 @@ public class HsOfficeDebitorController implements HsOfficeDebitorsApi {
         return ResponseEntity.ok(mapper.map(result.get(), HsOfficeDebitorResource.class, ENTITY_TO_RESOURCE_POSTMAPPER));
     }
 
+    @Override
+    @Transactional(readOnly = true)
+    @Timed("app.office.debitors.api.getSingleDebitorByDebitorNumber")
+    public ResponseEntity<HsOfficeDebitorResource> getSingleDebitorByDebitorNumber(
+            final String currentSubject,
+            final String assumedRoles,
+            final Integer debitorNumber) {
+
+        context.define(currentSubject, assumedRoles);
+
+        final var result = debitorRepo.findDebitorByDebitorNumber(debitorNumber);
+        if (result.isEmpty()) {
+            return ResponseEntity.notFound().build();
+        }
+        return ResponseEntity.ok(mapper.map(result.get(), HsOfficeDebitorResource.class, ENTITY_TO_RESOURCE_POSTMAPPER));
+    }
+
     @Override
     @Transactional
     @Timed("app.office.debitors.api.deleteDebitorByUuid")

src/main/java/net/hostsharing/hsadminng/hs/office/debitor/HsOfficeDebitorRepository.java

@@ -1,6 +1,7 @@
 package net.hostsharing.hsadminng.hs.office.debitor;
 
 import io.micrometer.core.annotation.Timed;
+import net.hostsharing.hsadminng.lambda.Reducer;
 import org.springframework.data.jpa.repository.Query;
 import org.springframework.data.repository.Repository;
 
@@ -13,21 +14,29 @@ public interface HsOfficeDebitorRepository extends Repository<HsOfficeDebitorEnt
     @Timed("app.office.debitors.repo.findByUuid")
     Optional<HsOfficeDebitorEntity> findByUuid(UUID id);
 
+    @Timed("app.office.debitors.repo.findDebitorByPartnerUuid")
+    List<HsOfficeDebitorEntity> findDebitorsByPartnerUuid(UUID partnerUuid);
+
     @Query("""
             SELECT debitor FROM HsOfficeDebitorEntity debitor
             JOIN HsOfficePartnerEntity partner
                     ON partner.partnerRel.holder = debitor.debitorRel.anchor
                         AND partner.partnerRel.type = 'PARTNER' AND debitor.debitorRel.type = 'DEBITOR'
                 WHERE partner.partnerNumber = :partnerNumber
-                  AND debitor.debitorNumberSuffix = :debitorNumberSuffix
+                  AND (:debitorNumberSuffix IS NULL OR debitor.debitorNumberSuffix = :debitorNumberSuffix)
             """)
     @Timed("app.office.debitors.repo.findDebitorByPartnerNumberAndDebitorNumberSuffix")
-    List<HsOfficeDebitorEntity> findDebitorByPartnerNumberAndDebitorNumberSuffix(int partnerNumber, String debitorNumberSuffix);
+    List<HsOfficeDebitorEntity> findDebitorByPartnerNumberAndOptionalDebitorNumberSuffix(int partnerNumber, String debitorNumberSuffix);
 
-    default List<HsOfficeDebitorEntity> findDebitorByDebitorNumber(int debitorNumber) {
+    default Optional<HsOfficeDebitorEntity> findDebitorByDebitorNumber(int debitorNumber) {
         final var partnerNumber = debitorNumber / 100;
         final String suffix = String.format("%02d", debitorNumber % 100);
-        final var result = findDebitorByPartnerNumberAndDebitorNumberSuffix(partnerNumber, suffix);
+        final var result = findDebitorByPartnerNumberAndOptionalDebitorNumberSuffix(partnerNumber, suffix);
+        return result.stream().reduce(Reducer::toSingleElement);
+    }
+
+    default List<HsOfficeDebitorEntity> findDebitorsByPartnerNumber(int partnerNumber) {
+        final var result = findDebitorByPartnerNumberAndOptionalDebitorNumberSuffix(partnerNumber, null);
         return result;
     }
 
@@ -50,7 +59,7 @@ public interface HsOfficeDebitorRepository extends Repository<HsOfficeDebitorEnt
                     OR contact.caption like concat(cast(:name as text), '%')
                """)
     @Timed("app.office.debitors.repo.findDebitorByOptionalNameLike")
-    List<HsOfficeDebitorEntity> findDebitorByOptionalNameLike(String name);
+    List<HsOfficeDebitorEntity> findDebitorsByOptionalNameLike(String name);
 
     @Timed("app.office.debitors.repo.save")
     HsOfficeDebitorEntity save(final HsOfficeDebitorEntity entity);

src/main/java/net/hostsharing/hsadminng/hs/office/membership/HsOfficeMembershipController.java

@@ -6,6 +6,7 @@ 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.hs.office.partner.HsOfficePartnerEntity;
 import net.hostsharing.hsadminng.mapper.StandardMapper;
 import org.springframework.beans.factory.annotation.Autowired;
 import org.springframework.http.ResponseEntity;
@@ -17,7 +18,7 @@ import java.util.List;
 import java.util.UUID;
 import java.util.function.BiConsumer;
 
-import static java.util.Optional.ofNullable;
+import static net.hostsharing.hsadminng.errors.Validate.validate;
 import static net.hostsharing.hsadminng.repr.TaggedNumber.cropTag;
 
 @RestController
@@ -39,16 +40,20 @@ public class HsOfficeMembershipController implements HsOfficeMembershipsApi {
             final String currentSubject,
             final String assumedRoles,
             final UUID partnerUuid,
-            final String memberNumber) {
+            final String partnerNumber) {
         context.define(currentSubject, assumedRoles);
 
-        final var entities = (memberNumber != null)
+        validate("partnerUuid, partnerNumber").atMaxOneNonNull(partnerUuid, partnerNumber);
-                ? ofNullable(membershipRepo.findMembershipByMemberNumber(
-                    cropTag(HsOfficeMembershipEntity.MEMBER_NUMBER_TAG, memberNumber))).stream()
-                    .toList()
-                : membershipRepo.findMembershipsByOptionalPartnerUuid(partnerUuid);
 
-        final var resources = mapper.mapList(entities, HsOfficeMembershipResource.class,
+        final var entities = partnerNumber != null
+                ? membershipRepo.findMembershipsByPartnerNumber(
+                        cropTag(HsOfficePartnerEntity.PARTNER_NUMBER_TAG, partnerNumber))
+                : partnerUuid != null
+                    ? membershipRepo.findMembershipsByPartnerUuid(partnerUuid)
+                    : membershipRepo.findAll();
+
+        final var resources = mapper.mapList(
+                entities, HsOfficeMembershipResource.class,
                 SEPA_MANDATE_ENTITY_TO_RESOURCE_POSTMAPPER);
         return ResponseEntity.ok(resources);
     }
@@ -72,7 +77,8 @@ public class HsOfficeMembershipController implements HsOfficeMembershipsApi {
                         .path("/api/hs/office/memberships/{id}")
                         .buildAndExpand(saved.getUuid())
                         .toUri();
-        final var mapped = mapper.map(saved, HsOfficeMembershipResource.class,
+        final var mapped = mapper.map(
+                saved, HsOfficeMembershipResource.class,
                 SEPA_MANDATE_ENTITY_TO_RESOURCE_POSTMAPPER);
         return ResponseEntity.created(uri).body(mapped);
     }
@@ -91,7 +97,27 @@ public class HsOfficeMembershipController implements HsOfficeMembershipsApi {
         if (result.isEmpty()) {
             return ResponseEntity.notFound().build();
         }
-        return ResponseEntity.ok(mapper.map(result.get(), HsOfficeMembershipResource.class,
+        return ResponseEntity.ok(mapper.map(
+                result.get(), HsOfficeMembershipResource.class,
+                SEPA_MANDATE_ENTITY_TO_RESOURCE_POSTMAPPER));
+    }
+
+    @Override
+    @Transactional(readOnly = true)
+    @Timed("app.office.membership.api.getSingleMembershipByMembershipNumber")
+    public ResponseEntity<HsOfficeMembershipResource> getSingleMembershipByMembershipNumber(
+            final String currentSubject,
+            final String assumedRoles,
+            final Integer membershipNumber) {
+
+        context.define(currentSubject, assumedRoles);
+
+        final var result = membershipRepo.findMembershipByMemberNumber(membershipNumber);
+        if (result.isEmpty()) {
+            return ResponseEntity.notFound().build();
+        }
+        return ResponseEntity.ok(mapper.map(
+                result.get(), HsOfficeMembershipResource.class,
                 SEPA_MANDATE_ENTITY_TO_RESOURCE_POSTMAPPER));
     }
 

src/main/java/net/hostsharing/hsadminng/hs/office/membership/HsOfficeMembershipRepository.java

@@ -22,12 +22,19 @@ public interface HsOfficeMembershipRepository extends Repository<HsOfficeMembers
 
     @Query("""
             SELECT membership FROM HsOfficeMembershipEntity membership
-                WHERE ( CAST(:partnerUuid as org.hibernate.type.UUIDCharType) IS NULL
+                WHERE membership.partner.uuid = :partnerUuid
-                        OR membership.partner.uuid = :partnerUuid )
                 ORDER BY membership.partner.partnerNumber, membership.memberNumberSuffix
             """)
     @Timed("app.office.membership.repo.findMembershipsByOptionalPartnerUuid")
-    List<HsOfficeMembershipEntity> findMembershipsByOptionalPartnerUuid(UUID partnerUuid);
+    List<HsOfficeMembershipEntity> findMembershipsByPartnerUuid(UUID partnerUuid);
+
+    @Query("""
+            SELECT membership FROM HsOfficeMembershipEntity membership
+                WHERE membership.partner.partnerNumber = :partnerNumber
+                ORDER BY membership.partner.partnerNumber, membership.memberNumberSuffix
+            """)
+    @Timed("app.office.membership.repo.findMembershipsByPartnerNumber")
+    List<HsOfficeMembershipEntity> findMembershipsByPartnerNumber(Integer partnerNumber);
 
     @Query("""
             SELECT membership FROM HsOfficeMembershipEntity membership
@@ -35,12 +42,12 @@ public interface HsOfficeMembershipRepository extends Repository<HsOfficeMembers
                     AND (membership.memberNumberSuffix = :suffix)
                 ORDER BY membership.memberNumberSuffix
                """)
-    @Timed("app.office.membership.repo.findMembershipByPartnerNumberAndSuffix")
+    @Timed("app.office.membership.repo.findMembershipByMemberNumber")
-    HsOfficeMembershipEntity findMembershipByPartnerNumberAndSuffix(
+    Optional<HsOfficeMembershipEntity> findMembershipByPartnerNumberAndSuffix(
             @NotNull Integer partnerNumber,
             @NotNull String suffix);
 
-    default HsOfficeMembershipEntity findMembershipByMemberNumber(Integer memberNumber) {
+    default Optional<HsOfficeMembershipEntity> findMembershipByMemberNumber(final Integer memberNumber) {
         final var partnerNumber = memberNumber / 100;
         final String suffix = String.format("%02d", memberNumber % 100);
         final var result = findMembershipByPartnerNumberAndSuffix(partnerNumber, suffix);

src/main/java/net/hostsharing/hsadminng/hs/office/partner/HsOfficePartnerController.java

@@ -104,6 +104,23 @@ public class HsOfficePartnerController implements HsOfficePartnersApi {
         return ResponseEntity.ok(mapper.map(result.get(), HsOfficePartnerResource.class));
     }
 
+    @Override
+    @Transactional(readOnly = true)
+    @Timed("app.office.partners.api.getSinglePartnerByPartnerNumber")
+    public ResponseEntity<HsOfficePartnerResource> getSinglePartnerByPartnerNumber(
+            final String currentSubject,
+            final String assumedRoles,
+            final Integer partnerNumber) {
+
+        context.define(currentSubject, assumedRoles);
+
+        final var result = partnerRepo.findPartnerByPartnerNumber(partnerNumber);
+        if (result.isEmpty()) {
+            return ResponseEntity.notFound().build();
+        }
+        return ResponseEntity.ok(mapper.map(result.get(), HsOfficePartnerResource.class));
+    }
+
     @Override
     @Transactional
     @Timed("app.office.partners.api.deletePartnerByUuid")

src/main/java/net/hostsharing/hsadminng/hs/office/partner/HsOfficePartnerRepository.java

@@ -32,7 +32,7 @@ public interface HsOfficePartnerRepository extends Repository<HsOfficePartnerEnt
     List<HsOfficePartnerEntity> findPartnerByOptionalNameLike(String name);
 
     @Timed("app.office.partners.repo.findPartnerByPartnerNumber")
-    HsOfficePartnerEntity findPartnerByPartnerNumber(Integer partnerNumber);
+    Optional<HsOfficePartnerEntity> findPartnerByPartnerNumber(Integer partnerNumber);
 
     @Timed("app.office.partners.repo.save")
     HsOfficePartnerEntity save(final HsOfficePartnerEntity entity);

src/main/resources/api-definition/hs-office/api-mappings.yaml

@@ -13,6 +13,7 @@ map:
         - type: string:uuid => java.util.UUID
         - type: string:format => java.lang.String
         - type: number:currency => java.math.BigDecimal
+        - type: number:integer => java.lang.Integer
 
     paths:
         /api/hs/office/partners/{partnerUUID}:

src/main/resources/api-definition/hs-office/hs-office-coopassets-schemas.yaml

@@ -27,8 +27,6 @@ components:
                     nullable: false
                 membership.memberNumber:
                     type: string
-                    minLength: 9
-                    maxLength: 9
                     pattern: 'M-[0-9]{7}'
                 transactionType:
                     $ref: '#/components/schemas/HsOfficeCoopAssetsTransactionType'
@@ -69,8 +67,6 @@ components:
                     nullable: false
                 membership.memberNumber:
                     type: string
-                    minLength: 9
-                    maxLength: 9
                     pattern: 'M-[0-9]{7}'
                 transactionType:
                     $ref: '#/components/schemas/HsOfficeCoopAssetsTransactionType'
@@ -130,8 +126,6 @@ components:
                     format: uuid
                 adoptingMembership.memberNumber:
                     type: string
-                    minLength: 9
-                    maxLength: 9
                     pattern: 'M-[0-9]{7}'
             required:
                 - membership.uuid

src/main/resources/api-definition/hs-office/hs-office-debitor-schemas.yaml

@@ -13,8 +13,6 @@ components:
                     $ref: 'hs-office-relation-schemas.yaml#/components/schemas/HsOfficeRelation'
                 debitorNumber:
                     type: string
-                    minLength: 9
-                    maxLength: 9
                     pattern: 'D-[0-9]{7}'
                 debitorNumberSuffix:
                     type: string

src/main/resources/api-definition/hs-office/hs-office-debitors-with-debitorNumber.yaml

@@ -0,0 +1,29 @@
+get:
+    tags:
+        - hs-office-debitors
+    description: 'Fetch a single debitor by its debitorNumber, if visible for the current subject.'
+    operationId: getSingleDebitorByDebitorNumber
+    parameters:
+        - $ref: 'auth.yaml#/components/parameters/currentSubject'
+        - $ref: 'auth.yaml#/components/parameters/assumedRoles'
+        - name: debitorNumber
+          in: path
+          required: true
+          schema:
+              type: number
+              format: integer
+              minimum: 1000000
+              maximum: 9999999
+          description: debitor-number of the debitor to fetch.
+    responses:
+        "200":
+            description: OK
+            content:
+                'application/json':
+                    schema:
+                        $ref: 'hs-office-debitor-schemas.yaml#/components/schemas/HsOfficeDebitor'
+
+        "401":
+            $ref: 'error-responses.yaml#/components/responses/Unauthorized'
+        "403":
+            $ref: 'error-responses.yaml#/components/responses/Forbidden'

src/main/resources/api-definition/hs-office/hs-office-debitors.yaml

@@ -13,15 +13,20 @@ get:
           schema:
               type: string
           description: Prefix of name properties from person or contact to filter the results.
-        - name: debitorNumber
+        - name: partnerUuid
           in: query
           required: false
           schema:
               type: string
-              minLength: 9
+              format: uuid
-              maxLength: 9
+          description: UUID of the business partner, exclusive to `memberNumber`.
-              pattern: 'D-[0-9]{7}'
+        - name: partnerNumber
-          description: Debitor number of the requested debitor.
+          in: query
+          required: false
+          schema:
+              type: string
+              pattern: 'P-[0-9]{5}'
+          description: Partner number of the requested debitor.
     responses:
         "200":
             description: OK

src/main/resources/api-definition/hs-office/hs-office-membership-schemas.yaml

@@ -27,14 +27,10 @@ components:
                     $ref: 'hs-office-debitor-schemas.yaml#/components/schemas/HsOfficeDebitor'
                 memberNumber:
                     type: string
-                    minLength: 9
-                    maxLength: 9
                     pattern: 'M-[0-9]{7}'
                 memberNumberSuffix:
                     type: string
-                    minLength: 2
+                    pattern: '[0-9]{2}'
-                    maxLength: 2
-                    pattern: '[0-9]+'
                 validFrom:
                    type: string
                    format: date
@@ -69,9 +65,7 @@ components:
                     nullable: false
                 memberNumberSuffix:
                     type: string
-                    minLength: 2
+                    pattern: '[0-9]{2}'
-                    maxLength: 2
-                    pattern: '[0-9]+'
                     nullable: false
                 validFrom:
                     type: string

src/main/resources/api-definition/hs-office/hs-office-memberships-with-membershipNumber.yaml

@@ -0,0 +1,29 @@
+get:
+    tags:
+        - hs-office-memberships
+    description: 'Fetch a single membership by its membershipNumber, if visible for the current subject.'
+    operationId: getSingleMembershipByMembershipNumber
+    parameters:
+        - $ref: 'auth.yaml#/components/parameters/currentSubject'
+        - $ref: 'auth.yaml#/components/parameters/assumedRoles'
+        - name: membershipNumber
+          in: path
+          required: true
+          schema:
+              type: number
+              format: integer
+              minimum: 1000000
+              maximum: 9999999
+          description: membershipNumber of the membership to fetch.
+    responses:
+        "200":
+            description: OK
+            content:
+                'application/json':
+                    schema:
+                        $ref: 'hs-office-membership-schemas.yaml#/components/schemas/HsOfficeMembership'
+
+        "401":
+            $ref: 'error-responses.yaml#/components/responses/Unauthorized'
+        "403":
+            $ref: 'error-responses.yaml#/components/responses/Forbidden'

src/main/resources/api-definition/hs-office/hs-office-memberships.yaml

@@ -15,15 +15,13 @@ get:
               type: string
               format: uuid
           description: UUID of the business partner, exclusive to `memberNumber`.
-        - name: memberNumber
+        - name: partnerNumber
           in: query
           required: false
           schema:
               type: string
-              minLength: 9
+              pattern: 'P-[0-9]{5}'
-              maxLength: 9
+          description: partnerNumber of the partner the memberships belong to
-              pattern: 'M-[0-9]{7}'
-          description: Member number, exclusive to `partnerUuid`.
     responses:
         "200":
             description: OK

src/main/resources/api-definition/hs-office/hs-office-partner-schemas.yaml

@@ -11,8 +11,6 @@ components:
                     format: uuid
                 partnerNumber:
                     type: string
-                    minLength: 7
-                    maxLength: 7
                     pattern: 'P-[0-9]{5}'
                 partnerRel:
                     $ref: 'hs-office-relation-schemas.yaml#/components/schemas/HsOfficeRelation'
@@ -87,8 +85,6 @@ components:
             properties:
                 partnerNumber:
                     type: string
-                    minLength: 7
-                    maxLength: 7
                     pattern: 'P-[0-9]{5}'
                 partnerRel:
                     $ref: '#/components/schemas/HsOfficePartnerRelInsert'

src/main/resources/api-definition/hs-office/hs-office-partners-with-partnerNumber.yaml

@@ -0,0 +1,28 @@
+get:
+    tags:
+        - hs-office-partners
+    description: 'Fetch a single business partner by its partner-number (prefixed with "P-"), if visible for the current subject.'
+    operationId: getSinglePartnerByPartnerNumber
+    parameters:
+        - $ref: 'auth.yaml#/components/parameters/currentSubject'
+        - $ref: 'auth.yaml#/components/parameters/assumedRoles'
+        - name: partnerNumber
+          in: path
+          required: true
+          schema:
+              type: integer
+              minimum: 10000
+              maximum: 99999
+          description: partner-number (prefixed with "P-") of the partner to fetch.
+    responses:
+        "200":
+            description: OK
+            content:
+                'application/json':
+                    schema:
+                        $ref: 'hs-office-partner-schemas.yaml#/components/schemas/HsOfficePartner'
+
+        "401":
+            $ref: 'error-responses.yaml#/components/responses/Unauthorized'
+        "403":
+            $ref: 'error-responses.yaml#/components/responses/Forbidden'

src/main/resources/api-definition/hs-office/hs-office.yaml

@@ -13,6 +13,9 @@ paths:
   /api/hs/office/partners:
     $ref: "hs-office-partners.yaml"
 
+  /api/hs/office/partners/P-{partnerNumber}:
+    $ref: "hs-office-partners-with-partnerNumber.yaml"
+
   /api/hs/office/partners/{partnerUUID}:
     $ref: "hs-office-partners-with-uuid.yaml"
 
@@ -58,6 +61,9 @@ paths:
   /api/hs/office/debitors:
     $ref: "hs-office-debitors.yaml"
 
+  /api/hs/office/debitors/D-{debitorNumber}:
+    $ref: "hs-office-debitors-with-debitorNumber.yaml"
+
   /api/hs/office/debitors/{debitorUUID}:
     $ref: "hs-office-debitors-with-uuid.yaml"
 
@@ -76,6 +82,9 @@ paths:
   /api/hs/office/memberships:
     $ref: "hs-office-memberships.yaml"
 
+  /api/hs/office/memberships/M-{membershipNumber}:
+    $ref: "hs-office-memberships-with-membershipNumber.yaml"
+
   /api/hs/office/memberships/{membershipUUID}:
     $ref: "hs-office-memberships-with-uuid.yaml"
 

src/test/java/net/hostsharing/hsadminng/errors/ValidateUnitTest.java

@@ -0,0 +1,31 @@
+package net.hostsharing.hsadminng.errors;
+
+import org.junit.jupiter.api.Test;
+
+import jakarta.validation.ValidationException;
+
+import static org.assertj.core.api.Assertions.assertThat;
+import static org.assertj.core.api.Assertions.catchThrowable;
+
+class ValidateUnitTest {
+
+    @Test
+    void shouldFailValidationIfBothParametersAreNotNull() {
+        final var throwable = catchThrowable(() ->
+            Validate.validate("var1, var2").atMaxOneNonNull("val1", "val2")
+        );
+        assertThat(throwable).isInstanceOf(ValidationException.class)
+                .hasMessage("Exactly one of (var1, var2) must be non-null, but are (val1, val2)");
+    }
+
+    @Test
+    void shouldNotFailValidationIfBothParametersAreull() {
+        Validate.validate("var1, var2").atMaxOneNonNull(null, null);
+    }
+
+    @Test
+    void shouldNotFailValidationIfExactlyOneParameterIsNonNull() {
+        Validate.validate("var1, var2").atMaxOneNonNull("val1", null);
+        Validate.validate("var1, var2").atMaxOneNonNull(null, "val2");
+    }
+}

src/test/java/net/hostsharing/hsadminng/hs/booking/item/HsBookingItemRepositoryIntegrationTest.java

@@ -120,7 +120,7 @@ class HsBookingItemRepositoryIntegrationTest extends ContextBasedTestWithCleanup
             // given
             context("superuser-alex@hostsharing.net");
             final var count = rbacBookingItemRepo.count();
-            final var givenDebitor = debitorRepo.findDebitorByOptionalNameLike("First").get(0);
+            final var givenDebitor = debitorRepo.findDebitorsByOptionalNameLike("First").get(0);
             final var givenProject = realProjectRepo.findAllByDebitorUuid(givenDebitor.getUuid()).get(0);
 
             // when
@@ -151,7 +151,7 @@ class HsBookingItemRepositoryIntegrationTest extends ContextBasedTestWithCleanup
 
             // when
             attempt(em, () -> {
-                final var givenDebitor = debitorRepo.findDebitorByOptionalNameLike("First").get(0);
+                final var givenDebitor = debitorRepo.findDebitorsByOptionalNameLike("First").get(0);
                 final var givenProject = realProjectRepo.findAllByDebitorUuid(givenDebitor.getUuid()).get(0);
                 final var newBookingItem = HsBookingItemRbacEntity.builder()
                         .project(givenProject)

src/test/java/net/hostsharing/hsadminng/hs/office/coopassets/HsOfficeCoopAssetsTransactionControllerAcceptanceTest.java

@@ -79,7 +79,7 @@ class HsOfficeCoopAssetsTransactionControllerAcceptanceTest extends ContextBased
         void globalAdmin_canFindCoopAssetsTransactionsByMemberNumber() {
 
             context.define("superuser-alex@hostsharing.net");
-            final var givenMembership = membershipRepo.findMembershipByMemberNumber(1000202);
+            final var givenMembership = membershipRepo.findMembershipByMemberNumber(1000202).orElseThrow();
 
             RestAssured // @formatter:off
                     .given()
@@ -202,7 +202,7 @@ class HsOfficeCoopAssetsTransactionControllerAcceptanceTest extends ContextBased
         void globalAdmin_canFindCoopAssetsTransactionsByMembershipUuidAndDateRange() {
 
             context.define("superuser-alex@hostsharing.net");
-            final var givenMembership = membershipRepo.findMembershipByMemberNumber(1000202);
+            final var givenMembership = membershipRepo.findMembershipByMemberNumber(1000202).orElseThrow();
 
             RestAssured // @formatter:off
                 .given()
@@ -235,7 +235,7 @@ class HsOfficeCoopAssetsTransactionControllerAcceptanceTest extends ContextBased
         void globalAdmin_canPostNewCoopAssetTransaction() {
 
             context.define("superuser-alex@hostsharing.net");
-            final var givenMembership = membershipRepo.findMembershipByMemberNumber(1000101);
+            final var givenMembership = membershipRepo.findMembershipByMemberNumber(1000101).orElseThrow();
 
             final var location = RestAssured // @formatter:off
                     .given()
@@ -280,7 +280,7 @@ class HsOfficeCoopAssetsTransactionControllerAcceptanceTest extends ContextBased
         void globalAdmin_canAddCoopAssetsReversalTransaction() {
 
             context.define("superuser-alex@hostsharing.net");
-            final var givenMembership = membershipRepo.findMembershipByMemberNumber(1000101);
+            final var givenMembership = membershipRepo.findMembershipByMemberNumber(1000101).orElseThrow();
             final var givenTransaction = jpaAttempt.transacted(() -> {
                 // TODO.impl: introduce something like transactedAsSuperuser / transactedAs("...", ...)
                 context.define("superuser-alex@hostsharing.net");
@@ -348,7 +348,7 @@ class HsOfficeCoopAssetsTransactionControllerAcceptanceTest extends ContextBased
         void globalAdmin_canNotCancelMoreAssetsThanCurrentlySubscribed() {
 
             context.define("superuser-alex@hostsharing.net");
-            final var givenMembership = membershipRepo.findMembershipByMemberNumber(1000101);
+            final var givenMembership = membershipRepo.findMembershipByMemberNumber(1000101).orElseThrow();
 
             RestAssured // @formatter:off
                 .given()

src/test/java/net/hostsharing/hsadminng/hs/office/coopassets/HsOfficeCoopAssetsTransactionControllerRestTest.java

@@ -915,7 +915,7 @@ class HsOfficeCoopAssetsTransactionControllerRestTest {
                 AVAILABLE_MEMBER_ENTITY);
 
         final var availableMemberNumber = Integer.valueOf(AVAILABLE_TARGET_MEMBER_NUMBER.substring("M-".length()));
-        when(membershipRepo.findMembershipByMemberNumber(eq(availableMemberNumber))).thenReturn(AVAILABLE_MEMBER_ENTITY);
+        when(membershipRepo.findMembershipByMemberNumber(eq(availableMemberNumber))).thenReturn(Optional.of(AVAILABLE_MEMBER_ENTITY));
 
         when(membershipRepo.findByUuid(eq(ORIGIN_MEMBERSHIP_UUID))).thenReturn(Optional.of(ORIGIN_TARGET_MEMBER_ENTITY));
         when(membershipRepo.findByUuid(eq(AVAILABLE_TARGET_MEMBERSHIP_UUID))).thenReturn(Optional.of(AVAILABLE_MEMBER_ENTITY));

src/test/java/net/hostsharing/hsadminng/hs/office/coopassets/HsOfficeCoopAssetsTransactionRepositoryIntegrationTest.java

@@ -62,7 +62,7 @@ class HsOfficeCoopAssetsTransactionRepositoryIntegrationTest extends ContextBase
             // given
             context("superuser-alex@hostsharing.net");
             final var count = coopAssetsTransactionRepo.count();
-            final var givenMembership = membershipRepo.findMembershipByMemberNumber(1000101).load();
+            final var givenMembership = membershipRepo.findMembershipByMemberNumber(1000101).orElseThrow().load();
 
             // when
             final var result = attempt(em, () -> {
@@ -94,7 +94,7 @@ class HsOfficeCoopAssetsTransactionRepositoryIntegrationTest extends ContextBase
 
             // when
             attempt(em, () -> {
-                final var givenMembership = membershipRepo.findMembershipByMemberNumber(1000101);
+                final var givenMembership = membershipRepo.findMembershipByMemberNumber(1000101).orElseThrow();
                 final var newCoopAssetsTransaction = HsOfficeCoopAssetsTransactionEntity.builder()
                         .membership(givenMembership)
                         .transactionType(HsOfficeCoopAssetsTransactionType.DEPOSIT)
@@ -166,7 +166,7 @@ class HsOfficeCoopAssetsTransactionRepositoryIntegrationTest extends ContextBase
         public void globalAdmin_canViewCoopAssetsTransactions_filteredByMembershipUuid() {
             // given
             context("superuser-alex@hostsharing.net");
-            final var givenMembership = membershipRepo.findMembershipByMemberNumber(1000202);
+            final var givenMembership = membershipRepo.findMembershipByMemberNumber(1000202).orElseThrow();
 
             // when
             final var result = coopAssetsTransactionRepo.findCoopAssetsTransactionByOptionalMembershipUuidAndDateRange(
@@ -189,7 +189,7 @@ class HsOfficeCoopAssetsTransactionRepositoryIntegrationTest extends ContextBase
         public void globalAdmin_canViewCoopAssetsTransactions_filteredByMembershipUuidAndValueDateRange() {
             // given
             context("superuser-alex@hostsharing.net");
-            final var givenMembership = membershipRepo.findMembershipByMemberNumber(1000202);
+            final var givenMembership = membershipRepo.findMembershipByMemberNumber(1000202).orElseThrow();
 
             // when
             final var result = coopAssetsTransactionRepo.findCoopAssetsTransactionByOptionalMembershipUuidAndDateRange(

src/test/java/net/hostsharing/hsadminng/hs/office/coopshares/HsOfficeCoopSharesTransactionControllerAcceptanceTest.java

@@ -87,7 +87,7 @@ class HsOfficeCoopSharesTransactionControllerAcceptanceTest extends ContextBased
         void globalAdmin_canFindCoopSharesTransactionsByMemberNumber() {
 
             context.define("superuser-alex@hostsharing.net");
-            final var givenMembership = membershipRepo.findMembershipByMemberNumber(1000202);
+            final var givenMembership = membershipRepo.findMembershipByMemberNumber(1000202).orElseThrow();
 
             RestAssured // @formatter:off
                 .given().header("current-subject", "superuser-alex@hostsharing.net").port(port).when().get("http://localhost/api/hs/office/coopsharestransactions?membershipUuid=" + givenMembership.getUuid()).then().log().all().assertThat().statusCode(200).contentType("application/json").body("", lenientlyEquals("""
@@ -142,7 +142,7 @@ class HsOfficeCoopSharesTransactionControllerAcceptanceTest extends ContextBased
         void globalAdmin_canFindCoopSharesTransactionsByMembershipUuidAndDateRange() {
 
             context.define("superuser-alex@hostsharing.net");
-            final var givenMembership = membershipRepo.findMembershipByMemberNumber(1000202);
+            final var givenMembership = membershipRepo.findMembershipByMemberNumber(1000202).orElseThrow();
 
             RestAssured // @formatter:off
                 .given().header("current-subject", "superuser-alex@hostsharing.net").port(port).when()
@@ -167,7 +167,7 @@ class HsOfficeCoopSharesTransactionControllerAcceptanceTest extends ContextBased
         void globalAdmin_canAddCoopSharesTransaction() {
 
             context.define("superuser-alex@hostsharing.net");
-            final var givenMembership = membershipRepo.findMembershipByMemberNumber(1000101);
+            final var givenMembership = membershipRepo.findMembershipByMemberNumber(1000101).orElseThrow();
 
             final var location = RestAssured // @formatter:off
                 .given().header("current-subject", "superuser-alex@hostsharing.net").contentType(ContentType.JSON).body("""
@@ -198,7 +198,7 @@ class HsOfficeCoopSharesTransactionControllerAcceptanceTest extends ContextBased
         void globalAdmin_canAddCoopSharesReversalTransaction() {
 
             context.define("superuser-alex@hostsharing.net");
-            final var givenMembership = membershipRepo.findMembershipByMemberNumber(1000101);
+            final var givenMembership = membershipRepo.findMembershipByMemberNumber(1000101).orElseThrow();
             final var givenTransaction = jpaAttempt.transacted(() -> {
                 // TODO.impl: introduce something like transactedAsSuperuser / transactedAs("...", ...)
                 context.define("superuser-alex@hostsharing.net");
@@ -266,7 +266,7 @@ class HsOfficeCoopSharesTransactionControllerAcceptanceTest extends ContextBased
         void globalAdmin_canNotCancelMoreSharesThanCurrentlySubscribed() {
 
             context.define("superuser-alex@hostsharing.net");
-            final var givenMembership = membershipRepo.findMembershipByMemberNumber(1000101);
+            final var givenMembership = membershipRepo.findMembershipByMemberNumber(1000101).orElseThrow();
 
             RestAssured // @formatter:off
                 .given().header("current-subject", "superuser-alex@hostsharing.net").contentType(ContentType.JSON).body("""

src/test/java/net/hostsharing/hsadminng/hs/office/coopshares/HsOfficeCoopSharesTransactionRepositoryIntegrationTest.java

@@ -61,7 +61,7 @@ class HsOfficeCoopSharesTransactionRepositoryIntegrationTest extends ContextBase
             // given
             context("superuser-alex@hostsharing.net");
             final var count = coopSharesTransactionRepo.count();
-            final var givenMembership = membershipRepo.findMembershipByMemberNumber(1000101).load();
+            final var givenMembership = membershipRepo.findMembershipByMemberNumber(1000101).orElseThrow().load();
 
             // when
             final var result = attempt(em, () -> {
@@ -93,7 +93,7 @@ class HsOfficeCoopSharesTransactionRepositoryIntegrationTest extends ContextBase
 
             // when
             attempt(em, () -> {
-                final var givenMembership = membershipRepo.findMembershipByMemberNumber(1000101);
+                final var givenMembership = membershipRepo.findMembershipByMemberNumber(1000101).orElseThrow();
                 final var newCoopSharesTransaction = HsOfficeCoopSharesTransactionEntity.builder()
                         .membership(givenMembership)
                         .transactionType(HsOfficeCoopSharesTransactionType.SUBSCRIPTION)
@@ -159,7 +159,7 @@ class HsOfficeCoopSharesTransactionRepositoryIntegrationTest extends ContextBase
         public void globalAdmin_canViewCoopSharesTransactions_filteredByMembershipUuid() {
             // given
             context("superuser-alex@hostsharing.net");
-            final var givenMembership = membershipRepo.findMembershipByMemberNumber(1000202);
+            final var givenMembership = membershipRepo.findMembershipByMemberNumber(1000202).orElseThrow();
 
             // when
             final var result = coopSharesTransactionRepo.findCoopSharesTransactionByOptionalMembershipUuidAndDateRange(
@@ -180,7 +180,7 @@ class HsOfficeCoopSharesTransactionRepositoryIntegrationTest extends ContextBase
         public void globalAdmin_canViewCoopSharesTransactions_filteredByMembershipUuidAndValueDateRange() {
             // given
             context("superuser-alex@hostsharing.net");
-            final var givenMembership = membershipRepo.findMembershipByMemberNumber(1000202);
+            final var givenMembership = membershipRepo.findMembershipByMemberNumber(1000202).orElseThrow();
 
             // when
             final var result = coopSharesTransactionRepo.findCoopSharesTransactionByOptionalMembershipUuidAndDateRange(

src/test/java/net/hostsharing/hsadminng/hs/office/debitor/HsOfficeDebitorControllerAcceptanceTest.java

@@ -31,7 +31,10 @@ import static net.hostsharing.hsadminng.hs.office.relation.HsOfficeRelationType.
 import static net.hostsharing.hsadminng.rbac.test.IsValidUuidMatcher.isUuidValid;
 import static net.hostsharing.hsadminng.rbac.test.JsonMatcher.lenientlyEquals;
 import static org.assertj.core.api.Assertions.assertThat;
-import static org.hamcrest.Matchers.*;
+import static org.hamcrest.Matchers.containsString;
+import static org.hamcrest.Matchers.equalTo;
+import static org.hamcrest.Matchers.is;
+import static org.hamcrest.Matchers.startsWith;
 
 @SpringBootTest(
         webEnvironment = SpringBootTest.WebEnvironment.RANDOM_PORT,
@@ -74,6 +77,69 @@ class HsOfficeDebitorControllerAcceptanceTest extends ContextBasedTestWithCleanu
     @PersistenceContext
     EntityManager em;
 
+    @Nested
+    class GetSingleDebitor {
+
+        @Test
+        void globalAdmin_withoutAssumedRoles_canGetDebitorByDebitorUuid() {
+
+            final var givenDebitor = jpaAttempt.transacted(() -> {
+                context("superuser-alex@hostsharing.net");
+                return debitorRepo.findDebitorByDebitorNumber(1000212).orElseThrow();
+            }).assertSuccessful().returnedValue();
+
+            RestAssured // @formatter:off
+                .given()
+                    .header("current-subject", "superuser-alex@hostsharing.net")
+                    .port(port)
+                .when()
+                    .get("http://localhost/api/hs/office/debitors/" + givenDebitor.getUuid())
+                .then().log().all().assertThat()
+                    .statusCode(200)
+                    .contentType("application/json")
+                    .body("", lenientlyEquals("""
+                        {
+                            "debitorNumber": "D-1000212",
+                            "partner": { "partnerNumber": "P-10002" },
+                            "debitorRel": {
+                               "contact": { "caption": "second contact" }
+                            },
+                            "vatId": null,
+                            "vatCountryCode": null,
+                            "vatBusiness": true
+                        }
+                        """));
+            // @formatter:on
+        }
+
+        @Test
+        void globalAdmin_withoutAssumedRoles_canGetDebitorByDebitorNumber() {
+
+            RestAssured // @formatter:off
+                .given()
+                    .header("current-subject", "superuser-alex@hostsharing.net")
+                    .port(port)
+                .when()
+                    .get("http://localhost/api/hs/office/debitors/D-1000212")
+                .then().log().all().assertThat()
+                    .statusCode(200)
+                    .contentType("application/json")
+                    .body("", lenientlyEquals("""
+                         {
+                             "debitorNumber": "D-1000212",
+                             "partner": { "partnerNumber": "P-10002" },
+                             "debitorRel": {
+                                "contact": { "caption": "second contact" }
+                             },
+                             "vatId": null,
+                             "vatCountryCode": null,
+                             "vatBusiness": true
+                         }
+                        """));
+            // @formatter:on
+        }
+    }
+
     @Nested
     class GetListOfDebitors {
 
@@ -233,32 +299,28 @@ class HsOfficeDebitorControllerAcceptanceTest extends ContextBasedTestWithCleanu
         }
 
         @Test
-        void globalAdmin_withoutAssumedRoles_canFindDebitorDebitorByDebitorNumber() {
+        void globalAdmin_withoutAssumedRoles_canFindDebitorsByPartnerNumber() {
 
             RestAssured // @formatter:off
-                    .given()
+                .given()
                     .header("current-subject", "superuser-alex@hostsharing.net")
                     .port(port)
-                    .when()
+                .when()
-                    .get("http://localhost/api/hs/office/debitors?debitorNumber=D-1000212")
+                    .get("http://localhost/api/hs/office/debitors?partnerNumber=P-10002")
-                    .then().log().all().assertThat()
+                .then().log().all().assertThat()
                     .statusCode(200)
                     .contentType("application/json")
                     .body("", lenientlyEquals("""
-                     [
+                    [
-                         {
+                        {
-                             "debitorNumber": "D-1000212",
+                            "debitorNumber": "D-1000212",
-                             "partner": { "partnerNumber": "P-10002" },
+                            "partner": {
-                             "debitorRel": {
+                                "partnerNumber": "P-10002"
-                                "contact": { "caption": "second contact" }
+                            }
-                             },
+                        }
-                             "vatId": null,
+                    ]
-                             "vatCountryCode": null,
-                             "vatBusiness": true
-                         }
-                     ]
                     """));
-            // @formatter:on
+                    // @formatter:on
         }
     }
 
@@ -444,7 +506,7 @@ class HsOfficeDebitorControllerAcceptanceTest extends ContextBasedTestWithCleanu
         @Test
         void globalAdmin_withoutAssumedRole_canGetArbitraryDebitor() {
             context.define("superuser-alex@hostsharing.net");
-            final var givenDebitorUuid = debitorRepo.findDebitorByOptionalNameLike("First").get(0).getUuid();
+            final var givenDebitorUuid = debitorRepo.findDebitorsByOptionalNameLike("First").get(0).getUuid();
 
             RestAssured // @formatter:off
                 .given()
@@ -509,7 +571,7 @@ class HsOfficeDebitorControllerAcceptanceTest extends ContextBasedTestWithCleanu
         @Test
         void normalUser_canNotGetUnrelatedDebitor() {
             context.define("superuser-alex@hostsharing.net");
-            final var givenDebitorUuid = debitorRepo.findDebitorByOptionalNameLike("First").get(0).getUuid();
+            final var givenDebitorUuid = debitorRepo.findDebitorsByOptionalNameLike("First").get(0).getUuid();
 
             RestAssured // @formatter:off
                 .given()
@@ -524,7 +586,7 @@ class HsOfficeDebitorControllerAcceptanceTest extends ContextBasedTestWithCleanu
         @Test
         void contactAdminUser_canGetRelatedDebitorExceptRefundBankAccount() {
             context.define("superuser-alex@hostsharing.net");
-            final var givenDebitorUuid = debitorRepo.findDebitorByOptionalNameLike("first contact").get(0).getUuid();
+            final var givenDebitorUuid = debitorRepo.findDebitorsByOptionalNameLike("first contact").get(0).getUuid();
 
             RestAssured // @formatter:off
                 .given()

src/test/java/net/hostsharing/hsadminng/hs/office/debitor/HsOfficeDebitorRepositoryIntegrationTest.java

@@ -50,7 +50,7 @@ class HsOfficeDebitorRepositoryIntegrationTest extends ContextBasedTestWithClean
     HsOfficePartnerRepository partnerRepo;
 
     @Autowired
-    HsOfficeContactRealRepository contactrealRepo;
+    HsOfficeContactRealRepository contactRealRepo;
 
     @Autowired
     HsOfficePersonRealRepository personRepo;
@@ -83,9 +83,9 @@ class HsOfficeDebitorRepositoryIntegrationTest extends ContextBasedTestWithClean
             // given
             context("superuser-alex@hostsharing.net");
             final var count = debitorRepo.count();
-            final var givenPartner = partnerRepo.findPartnerByPartnerNumber(10001);
+            final var givenPartner = partnerRepo.findPartnerByPartnerNumber(10001).orElseThrow();
             final var givenPartnerPerson = one(personRepo.findPersonByOptionalNameLike("First GmbH"));
-            final var givenContact = one(contactrealRepo.findContactByOptionalCaptionLike("first contact"));
+            final var givenContact = one(contactRealRepo.findContactByOptionalCaptionLike("first contact"));
 
             // when
             final var result = attempt(em, () -> {
@@ -119,7 +119,7 @@ class HsOfficeDebitorRepositoryIntegrationTest extends ContextBasedTestWithClean
             // given
             context("superuser-alex@hostsharing.net");
             final var givenPartnerPerson = one(personRepo.findPersonByOptionalNameLike("First GmbH"));
-            final var givenContact = one(contactrealRepo.findContactByOptionalCaptionLike("first contact"));
+            final var givenContact = one(contactRealRepo.findContactByOptionalCaptionLike("first contact"));
 
             // when
             final var result = attempt(em, () -> {
@@ -158,7 +158,7 @@ class HsOfficeDebitorRepositoryIntegrationTest extends ContextBasedTestWithClean
             attempt(em, () -> {
                 final var givenPartnerPerson = one(personRepo.findPersonByOptionalNameLike("First GmbH"));
                 final var givenDebitorPerson = one(personRepo.findPersonByOptionalNameLike("Fourth eG"));
-                final var givenContact = one(contactrealRepo.findContactByOptionalCaptionLike("fourth contact"));
+                final var givenContact = one(contactRealRepo.findContactByOptionalCaptionLike("fourth contact"));
                 final var newDebitor = HsOfficeDebitorEntity.builder()
                         .debitorNumberSuffix("22")
                         .debitorRel(HsOfficeRelationRealEntity.builder()
@@ -234,7 +234,7 @@ class HsOfficeDebitorRepositoryIntegrationTest extends ContextBasedTestWithClean
             context("superuser-alex@hostsharing.net");
 
             // when
-            final var result = debitorRepo.findDebitorByOptionalNameLike(null);
+            final var result = debitorRepo.findDebitorsByOptionalNameLike(null);
 
             // then
             allTheseDebitorsAreReturned(
@@ -256,7 +256,7 @@ class HsOfficeDebitorRepositoryIntegrationTest extends ContextBasedTestWithClean
             context("superuser-alex@hostsharing.net", assumedRole);
 
             // when:
-            final var result = debitorRepo.findDebitorByOptionalNameLike("");
+            final var result = debitorRepo.findDebitorsByOptionalNameLike("");
 
             // then:
             exactlyTheseDebitorsAreReturned(result,
@@ -270,7 +270,7 @@ class HsOfficeDebitorRepositoryIntegrationTest extends ContextBasedTestWithClean
             context("selfregistered-test-user@hostsharing.org");
 
             // when:
-            final var result = debitorRepo.findDebitorByOptionalNameLike(null);
+            final var result = debitorRepo.findDebitorsByOptionalNameLike(null);
 
             // then:
             assertThat(result).isEmpty();
@@ -278,7 +278,7 @@ class HsOfficeDebitorRepositoryIntegrationTest extends ContextBasedTestWithClean
     }
 
     @Nested
-    class FindByDebitorNumberLike {
+    class FindByDebitorNumber {
 
         @Test
         public void globalAdmin_canViewAllDebitors() {
@@ -288,6 +288,23 @@ class HsOfficeDebitorRepositoryIntegrationTest extends ContextBasedTestWithClean
             // when
             final var result = debitorRepo.findDebitorByDebitorNumber(1000313);
 
+            // then
+            assertThat(result).map(Object::toString).contains(
+                    "debitor(D-1000313: rel(anchor='IF Third OHG', type='DEBITOR', holder='IF Third OHG'), thi)");
+        }
+    }
+
+    @Nested
+    class FindByPartnerNumber {
+
+        @Test
+        public void globalAdmin_canViewAllDebitors() {
+            // given
+            context("superuser-alex@hostsharing.net");
+
+            // when
+            final var result = debitorRepo.findDebitorsByPartnerNumber(10003);
+
             // then
             exactlyTheseDebitorsAreReturned(result,
                     "debitor(D-1000313: rel(anchor='IF Third OHG', type='DEBITOR', holder='IF Third OHG'), thi)");
@@ -303,7 +320,7 @@ class HsOfficeDebitorRepositoryIntegrationTest extends ContextBasedTestWithClean
             context("superuser-alex@hostsharing.net");
 
             // when
-            final var result = debitorRepo.findDebitorByOptionalNameLike("third contact");
+            final var result = debitorRepo.findDebitorsByOptionalNameLike("third contact");
 
             // then
             exactlyTheseDebitorsAreReturned(result, "debitor(D-1000313: rel(anchor='IF Third OHG', type='DEBITOR', holder='IF Third OHG'), thi)");
@@ -324,7 +341,7 @@ class HsOfficeDebitorRepositoryIntegrationTest extends ContextBasedTestWithClean
                     "hs_office.relation#FourtheG-with-DEBITOR-FourtheG:ADMIN", true);
             final var givenNewPartnerPerson = one(personRepo.findPersonByOptionalNameLike("First"));
             final var givenNewBillingPerson = one(personRepo.findPersonByOptionalNameLike("Firby"));
-            final var givenNewContact = one(contactrealRepo.findContactByOptionalCaptionLike("sixth contact"));
+            final var givenNewContact = one(contactRealRepo.findContactByOptionalCaptionLike("sixth contact"));
             final var givenNewBankAccount = one(bankAccountRepo.findByOptionalHolderLike("first"));
             final String givenNewVatId = "NEW-VAT-ID";
             final String givenNewVatCountryCode = "NC";
@@ -613,7 +630,7 @@ class HsOfficeDebitorRepositoryIntegrationTest extends ContextBasedTestWithClean
             context("superuser-alex@hostsharing.net");
             final var givenPartner = one(partnerRepo.findPartnerByOptionalNameLike(partnerName));
             final var givenPartnerPerson = givenPartner.getPartnerRel().getHolder();
-            final var givenContact = one(contactrealRepo.findContactByOptionalCaptionLike(contactCaption));
+            final var givenContact = one(contactRealRepo.findContactByOptionalCaptionLike(contactCaption));
             final var givenBankAccount =
                     bankAccountHolder != null ? one(bankAccountRepo.findByOptionalHolderLike(bankAccountHolder)) : null;
             final var newDebitor = HsOfficeDebitorEntity.builder()

src/test/java/net/hostsharing/hsadminng/hs/office/membership/HsOfficeMembershipControllerAcceptanceTest.java

@@ -112,16 +112,16 @@ class HsOfficeMembershipControllerAcceptanceTest extends ContextBasedTestWithCle
         void globalAdmin_canViewMembershipsByPartnerUuid() {
 
             context.define("superuser-alex@hostsharing.net");
-            final var partner = partnerRepo.findPartnerByPartnerNumber(10001);
+            final var partner = partnerRepo.findPartnerByPartnerNumber(10001).orElseThrow();
 
             RestAssured // @formatter:off
-                    .given()
+                .given()
                     .header("current-subject", "superuser-alex@hostsharing.net")
                     .port(port)
-                    .when()
+                .when()
                     .queryParam("partnerUuid", partner.getUuid() )
                     .get("http://localhost/api/hs/office/memberships")
-                    .then().log().all().assertThat()
+                .then().log().all().assertThat()
                     .statusCode(200)
                     .contentType("application/json")
                     .body("", lenientlyEquals("""
@@ -140,30 +140,30 @@ class HsOfficeMembershipControllerAcceptanceTest extends ContextBasedTestWithCle
         }
 
         @Test
-        void globalAdmin_canViewMembershipsByMemberNumber() {
+        void globalAdmin_canViewMembershipsByPartnerNumber() {
 
             RestAssured // @formatter:off
                     .given()
-                    .header("current-subject", "superuser-alex@hostsharing.net")
+                        .header("current-subject", "superuser-alex@hostsharing.net")
-                    .port(port)
+                        .port(port)
                     .when()
-                    .queryParam("memberNumber", "M-1000202" )
+                        .queryParam("partnerNumber", "P-10002" )
-                    .get("http://localhost/api/hs/office/memberships")
+                        .get("http://localhost/api/hs/office/memberships")
                     .then().log().all().assertThat()
-                    .statusCode(200)
+                        .statusCode(200)
-                    .contentType("application/json")
+                        .contentType("application/json")
-                    .body("", lenientlyEquals("""
+                        .body("", lenientlyEquals("""
-                      [
+                          [
-                          {
+                              {
-                              "partner": { "partnerNumber": "P-10002" },
+                                  "partner": { "partnerNumber": "P-10002" },
-                              "memberNumber": "M-1000202",
+                                  "memberNumber": "M-1000202",
-                              "memberNumberSuffix": "02",
+                                  "memberNumberSuffix": "02",
-                              "validFrom": "2022-10-01",
+                                  "validFrom": "2022-10-01",
-                              "validTo": null,
+                                  "validTo": null,
-                              "status": "ACTIVE"
+                                  "status": "ACTIVE"
-                          }
+                              }
-                      ]
+                          ]
-                    """));
+                        """));
             // @formatter:on
         }
     }
@@ -220,7 +220,7 @@ class HsOfficeMembershipControllerAcceptanceTest extends ContextBasedTestWithCle
         @Test
         void globalAdmin_canGetArbitraryMembership() {
             context.define("superuser-alex@hostsharing.net");
-            final var givenMembershipUuid = membershipRepo.findMembershipByMemberNumber(1000101).getUuid();
+            final var givenMembershipUuid = membershipRepo.findMembershipByMemberNumber(1000101).orElseThrow().getUuid();
 
             RestAssured // @formatter:off
                 .given()
@@ -246,7 +246,7 @@ class HsOfficeMembershipControllerAcceptanceTest extends ContextBasedTestWithCle
         @Test
         void normalUser_canNotGetUnrelatedMembership() {
             context.define("superuser-alex@hostsharing.net");
-            final var givenMembershipUuid = membershipRepo.findMembershipByMemberNumber(1000101).getUuid();
+            final var givenMembershipUuid = membershipRepo.findMembershipByMemberNumber(1000101).orElseThrow().getUuid();
 
             RestAssured // @formatter:off
                 .given()
@@ -261,7 +261,7 @@ class HsOfficeMembershipControllerAcceptanceTest extends ContextBasedTestWithCle
         @Test
         void partnerRelAgent_canGetRelatedMembership() {
             context.define("superuser-alex@hostsharing.net");
-            final var givenMembershipUuid = membershipRepo.findMembershipByMemberNumber(1000303).getUuid();
+            final var givenMembershipUuid = membershipRepo.findMembershipByMemberNumber(1000303).orElseThrow().getUuid();
 
             RestAssured // @formatter:off
                 .given()

src/test/java/net/hostsharing/hsadminng/hs/office/membership/HsOfficeMembershipControllerRestTest.java

@@ -19,11 +19,16 @@ import org.springframework.test.context.ActiveProfiles;
 import org.springframework.test.web.servlet.MockMvc;
 import org.springframework.test.web.servlet.request.MockMvcRequestBuilders;
 
+import java.util.List;
+import java.util.Optional;
 import java.util.UUID;
 
+import static io.hypersistence.utils.hibernate.type.range.Range.localDateRange;
+import static net.hostsharing.hsadminng.rbac.test.JsonMatcher.lenientlyEquals;
 import static org.hamcrest.Matchers.containsString;
 import static org.hamcrest.Matchers.hasSize;
 import static org.hamcrest.Matchers.is;
+import static org.mockito.ArgumentMatchers.any;
 import static org.mockito.Mockito.when;
 import static org.springframework.test.web.servlet.result.MockMvcResultMatchers.jsonPath;
 import static org.springframework.test.web.servlet.result.MockMvcResultMatchers.status;
@@ -33,6 +38,34 @@ import static org.springframework.test.web.servlet.result.MockMvcResultMatchers.
 @ActiveProfiles("test")
 public class HsOfficeMembershipControllerRestTest {
 
+    private static final HsOfficePartnerEntity PARTNER_12345 = HsOfficePartnerEntity.builder()
+            .partnerNumber(12345)
+            .build();
+    public static final HsOfficeMembershipEntity MEMBERSHIP_1234501 = HsOfficeMembershipEntity.builder()
+            .partner(PARTNER_12345)
+            .memberNumberSuffix("01")
+            .validity(localDateRange("[2013-10-01,]"))
+            .status(HsOfficeMembershipStatus.ACTIVE)
+            .build();
+    public static final HsOfficeMembershipEntity MEMBERSHIP_1234500 = HsOfficeMembershipEntity.builder()
+            .partner(PARTNER_12345)
+            .memberNumberSuffix("00")
+            .validity(localDateRange("[2011-04-01,2016-12-31]"))
+            .status(HsOfficeMembershipStatus.CANCELLED)
+            .build();
+    public static final String MEMBERSHIP_1234501_JSON = """
+            {
+                "partner": {
+                    "partnerNumber":"P-12345"
+                },
+                "memberNumber": "M-1234500",
+                "memberNumberSuffix": "00",
+                "validFrom": "2011-04-01",
+                "validTo": "2016-12-30",
+                "status":"CANCELLED"
+            }
+            """;
+
     @Autowired
     MockMvc mockMvc;
 
@@ -52,11 +85,11 @@ public class HsOfficeMembershipControllerRestTest {
     class GetListOfMemberships {
 
         @Test
-        void findMembershipByNonExistingMemberNumberReturnsEmptyList() throws Exception {
+        void findMembershipByNonExistingPartnerNumberReturnsEmptyList() throws Exception {
 
             // when
             mockMvc.perform(MockMvcRequestBuilders
-                            .get("/api/hs/office/memberships?memberNumber=M-1234501")
+                            .get("/api/hs/office/memberships?partnerNumber=P-12345")
                             .header("current-subject", "superuser-alex@hostsharing.net")
                             .contentType(MediaType.APPLICATION_JSON)
                             .content("""
@@ -73,6 +106,116 @@ public class HsOfficeMembershipControllerRestTest {
                     .andExpect(status().is2xxSuccessful())
                     .andExpect(jsonPath("$", hasSize(0)));
         }
+
+        @Test
+        void findMembershipByExistingPartnerNumberReturnsAllRelatedMemberships() throws Exception {
+
+            // given
+            when(membershipRepo.findMembershipsByPartnerNumber(12345))
+                    .thenReturn(List.of(
+                            MEMBERSHIP_1234500,
+                            MEMBERSHIP_1234501
+                    ));
+
+            // when
+            mockMvc.perform(MockMvcRequestBuilders
+                            .get("/api/hs/office/memberships?partnerNumber=P-12345")
+                            .header("current-subject", "superuser-alex@hostsharing.net")
+                            .contentType(MediaType.APPLICATION_JSON)
+                            .content("""
+                                       {
+                                           "partner.uuid": null,
+                                           "memberNumberSuffix": "01",
+                                           "validFrom": "2022-10-13",
+                                           "membershipFeeBillable": "true"
+                                         }
+                                    """)
+                            .accept(MediaType.APPLICATION_JSON))
+
+                    // then
+                    .andExpect(status().is2xxSuccessful())
+                    .andExpect(jsonPath("$", hasSize(2)));
+        }
+    }
+
+    @Nested
+    class GetSingleMembership {
+
+        @Test
+        void byUuid() throws Exception {
+
+            // given
+            final var givenUuid = UUID.randomUUID();
+            when(membershipRepo.findByUuid(givenUuid)).thenReturn(
+                    Optional.of(MEMBERSHIP_1234500)
+            );
+
+            // when
+            mockMvc.perform(MockMvcRequestBuilders
+                            .get("/api/hs/office/memberships/" + givenUuid)
+                            .header("current-subject", "superuser-alex@hostsharing.net")
+                            .accept(MediaType.APPLICATION_JSON))
+
+                    // then
+                    .andExpect(status().is2xxSuccessful())
+                    .andExpect(jsonPath("$", lenientlyEquals(MEMBERSHIP_1234501_JSON)));
+        }
+
+        @Test
+        void byUnavailableUuid() throws Exception {
+
+            // given
+            when(membershipRepo.findByUuid(any(UUID.class))).thenReturn(
+                    Optional.empty()
+            );
+
+            // when
+            mockMvc.perform(MockMvcRequestBuilders
+                            .get("/api/hs/office/memberships/" + UUID.randomUUID())
+                            .header("current-subject", "superuser-alex@hostsharing.net")
+                            .accept(MediaType.APPLICATION_JSON))
+
+                    // then
+                    .andExpect(status().isNotFound());
+        }
+
+        @Test
+        void byMemberNumber() throws Exception {
+
+            // given
+            when(membershipRepo.findMembershipByMemberNumber(1234501)).thenReturn(
+                    Optional.of(MEMBERSHIP_1234500)
+            );
+
+            // when
+            mockMvc.perform(MockMvcRequestBuilders
+                            .get("/api/hs/office/memberships/M-1234501")
+                            .header("current-subject", "superuser-alex@hostsharing.net")
+                            .accept(MediaType.APPLICATION_JSON))
+
+                    // then
+                    .andExpect(status().is2xxSuccessful())
+                    .andExpect(jsonPath("$", lenientlyEquals(MEMBERSHIP_1234501_JSON)));
+        }
+
+        @Test
+        void byUnavailableMemberNumber() throws Exception {
+
+            // given
+            when(membershipRepo.findMembershipByMemberNumber(any(Integer.class))).thenReturn(
+                    Optional.empty()
+            );
+
+            // when
+            mockMvc.perform(MockMvcRequestBuilders
+                            .get("/api/hs/office/memberships/M-0000000")
+                            .header("current-subject", "superuser-alex@hostsharing.net")
+                            .accept(MediaType.APPLICATION_JSON))
+
+                    // then
+                    .andExpect(status().isNotFound());
+        }
+
     }
 
     @Nested
@@ -163,10 +306,10 @@ public class HsOfficeMembershipControllerRestTest {
 
         public enum InvalidMemberSuffixVariants {
             MISSING("", "[memberNumberSuffix must not be null but is \"null\"]"),
-            TOO_SMALL("\"memberNumberSuffix\": \"9\",", "memberNumberSuffix size must be between 2 and 2 but is \"9\""),
+            TOO_SMALL("\"memberNumberSuffix\": \"9\",", "memberNumberSuffix must match \"[0-9]{2}\" but is \"9\""),
-            TOO_LARGE("\"memberNumberSuffix\": \"100\",", "memberNumberSuffix size must be between 2 and 2 but is \"100\""),
+            TOO_LARGE("\"memberNumberSuffix\": \"100\",", "memberNumberSuffix must match \"[0-9]{2}\" but is \"100\""),
-            NOT_NUMERIC("\"memberNumberSuffix\": \"AA\",", "memberNumberSuffix must match \"[0-9]+\" but is \"AA\""),
+            NOT_NUMERIC("\"memberNumberSuffix\": \"AA\",", "memberNumberSuffix must match \"[0-9]{2}\" but is \"AA\""),
-            EMPTY("\"memberNumberSuffix\": \"\",", "memberNumberSuffix size must be between 2 and 2 but is \"\"");
+            EMPTY("\"memberNumberSuffix\": \"\",", "memberNumberSuffix must match \"[0-9]{2}\" but is \"\"");
 
             private final String memberNumberSuffixEntry;
             private final String expectedErrorMessage;

src/test/java/net/hostsharing/hsadminng/hs/office/membership/HsOfficeMembershipRepositoryIntegrationTest.java

@@ -156,7 +156,7 @@ class HsOfficeMembershipRepositoryIntegrationTest extends ContextBasedTestWithCl
             context("superuser-alex@hostsharing.net");
 
             // when
-            final var result = membershipRepo.findMembershipsByOptionalPartnerUuid(null);
+            final var result = membershipRepo.findAll();
 
             // then
             exactlyTheseMembershipsAreReturned(
@@ -173,7 +173,7 @@ class HsOfficeMembershipRepositoryIntegrationTest extends ContextBasedTestWithCl
             final var givenPartner = partnerRepo.findPartnerByOptionalNameLike("First").get(0);
 
             // when
-            final var result = membershipRepo.findMembershipsByOptionalPartnerUuid(givenPartner.getUuid());
+            final var result = membershipRepo.findMembershipsByPartnerUuid(givenPartner.getUuid());
 
             // then
             exactlyTheseMembershipsAreReturned(result,
@@ -186,7 +186,7 @@ class HsOfficeMembershipRepositoryIntegrationTest extends ContextBasedTestWithCl
             context("superuser-alex@hostsharing.net");
 
             // when
-            final var result = membershipRepo.findMembershipByMemberNumber(1000202);
+            final var result = membershipRepo.findMembershipByMemberNumber(1000202).orElseThrow();
 
             // then
             assertThat(result)
@@ -194,6 +194,34 @@ class HsOfficeMembershipRepositoryIntegrationTest extends ContextBasedTestWithCl
                     .extracting(Object::toString)
                     .isEqualTo("Membership(M-1000202, P-10002, [2022-10-01,), ACTIVE)");
         }
+
+        @Test
+        public void globalAdmin_withoutAssumedRole_canFindAllMembershipsByPartnerNumberAndSuffix() {
+            // given
+            context("superuser-alex@hostsharing.net");
+
+            // when
+            final var result = membershipRepo.findMembershipByPartnerNumberAndSuffix(10002, "02").orElseThrow();
+
+            // then
+            assertThat(result)
+                    .isNotNull()
+                    .extracting(Object::toString)
+                    .isEqualTo("Membership(M-1000202, P-10002, [2022-10-01,), ACTIVE)");
+        }
+
+        @Test
+        public void globalAdmin_withoutAssumedRole_canFindAllMembershipsByPartnerNumber() {
+            // given
+            context("superuser-alex@hostsharing.net");
+
+            // when
+            final var result = membershipRepo.findMembershipsByPartnerNumber(10002);
+
+            // then
+            exactlyTheseMembershipsAreReturned(result,
+                    "Membership(M-1000202, P-10002, [2022-10-01,), ACTIVE)");
+        }
     }
 
     @Nested
@@ -339,7 +367,7 @@ class HsOfficeMembershipRepositoryIntegrationTest extends ContextBasedTestWithCl
                 select currentTask, targetTable, targetOp, targetdelta->>'membernumbersuffix'
                     from base.tx_journal_v
                     where targettable = 'hs_office.membership';
-                    """);
+                """);
 
         // when
         @SuppressWarnings("unchecked") final List<Object[]> customerLogEntries = query.getResultList();

src/test/java/net/hostsharing/hsadminng/hs/office/partner/HsOfficePartnerControllerRestTest.java

@@ -168,6 +168,45 @@ class HsOfficePartnerControllerRestTest {
         }
     }
 
+    @Nested
+    class GetSinglePartnerByPartnerNumber {
+
+        @Test
+        void respondWithPartner_ifPartnerNumberIsAvailable() throws Exception {
+            // given
+            when(partnerRepo.findPartnerByPartnerNumber(12345)).thenReturn(Optional.of(HsOfficePartnerEntity.builder()
+                    .partnerNumber(12345)
+                    .build()));
+
+            // when
+            mockMvc.perform(MockMvcRequestBuilders
+                    .get("/api/hs/office/partners/P-12345")
+                    .header("current-subject", "superuser-alex@hostsharing.net")
+                    .contentType(MediaType.APPLICATION_JSON)
+                    .accept(MediaType.APPLICATION_JSON))
+
+            // then
+            .andExpect(status().isOk())
+            .andExpect(jsonPath("partnerNumber", is("P-12345")));
+        }
+
+        @Test
+        void respondNotFound_ifPartnerNumberIsNotAvailable() throws Exception {
+            // given
+            when(partnerRepo.findPartnerByPartnerNumber(12345)).thenReturn(Optional.empty());
+
+            // when
+            mockMvc.perform(MockMvcRequestBuilders
+                    .get("/api/hs/office/partners/P-12345")
+                    .header("current-subject", "superuser-alex@hostsharing.net")
+                    .contentType(MediaType.APPLICATION_JSON)
+                    .accept(MediaType.APPLICATION_JSON))
+
+            // then
+            .andExpect(status().isNotFound());
+        }
+    }
+
     @Nested
     class DeletePartner {
 

src/test/java/net/hostsharing/hsadminng/hs/office/partner/HsOfficePartnerRepositoryIntegrationTest.java

@@ -243,7 +243,7 @@ class HsOfficePartnerRepositoryIntegrationTest extends ContextBasedTestWithClean
             context("superuser-alex@hostsharing.net");
 
             // when
-            final var result = partnerRepo.findPartnerByPartnerNumber(10001);
+            final var result = partnerRepo.findPartnerByPartnerNumber(10001).orElseThrow();
 
             // then
             assertThat(result)

src/test/java/net/hostsharing/hsadminng/hs/office/scenarios/debitor/CreateSepaMandateForDebitor.java

@@ -17,9 +17,9 @@ public class CreateSepaMandateForDebitor extends UseCase<CreateSepaMandateForDeb
     protected HttpResponse run() {
 
         obtain("Debitor: Test AG - main debitor", () ->
-            httpGet("/api/hs/office/debitors?debitorNumber=&{debitorNumber}")
+            httpGet("/api/hs/office/debitors/%{debitorNumber}")
                     .expecting(OK).expecting(JSON),
-            response -> response.expectArrayElements(1).getFromBody("[0].uuid")
+            response -> response.getFromBody("uuid")
         );
 
         obtain("BankAccount: Test AG - debit bank account", () ->

src/test/java/net/hostsharing/hsadminng/hs/office/scenarios/membership/CancelMembership.java

@@ -18,9 +18,8 @@ public class CancelMembership extends UseCase<CancelMembership> {
     protected HttpResponse run() {
 
         obtain("Membership: %{memberNumber}", () ->
-                httpGet("/api/hs/office/memberships?memberNumber=%{memberNumber}")
+                httpGet("/api/hs/office/memberships/%{memberNumber}"),
-                        .expectArrayElements(1),
+                response -> response.getFromBody("uuid")
-                response -> response.expectArrayElements(1).getFromBody("[0].uuid")
         );
 
         return withTitle("Patch the New Status Into the Membership", () ->

src/test/java/net/hostsharing/hsadminng/hs/office/scenarios/membership/coopassets/CreateCoopAssetsTransaction.java

@@ -18,9 +18,9 @@ public abstract class CreateCoopAssetsTransaction extends UseCase<CreateCoopAsse
     protected HttpResponse run() {
 
         obtain("#{Find }membershipUuid", () ->
-            httpGet("/api/hs/office/memberships?memberNumber=&{memberNumber}")
+            httpGet("/api/hs/office/memberships/%{memberNumber}")
-                    .expecting(OK).expecting(JSON).expectArrayElements(1),
+                    .expecting(OK).expecting(JSON),
-            response -> response.getFromBody("$[0].uuid")
+            response -> response.getFromBody("uuid")
         );
 
         return withTitle("Create the Coop-Assets-%{transactionType} Transaction", () ->

src/test/java/net/hostsharing/hsadminng/hs/office/scenarios/membership/coopshares/CreateCoopSharesTransaction.java

@@ -18,9 +18,9 @@ public abstract class CreateCoopSharesTransaction extends UseCase<CreateCoopShar
     protected HttpResponse run() {
 
         obtain("#{Find }membershipUuid", () ->
-            httpGet("/api/hs/office/memberships?memberNumber=&{memberNumber}")
+            httpGet("/api/hs/office/memberships/%{memberNumber}")
-                    .expecting(OK).expecting(JSON).expectArrayElements(1),
+                    .expecting(OK).expecting(JSON),
-            response -> response.getFromBody("$[0].uuid")
+            response -> response.getFromBody("uuid")
         );
 
         return withTitle("Create the Coop-Shares-%{transactionType} Transaction", () ->

src/test/java/net/hostsharing/hsadminng/hs/office/sepamandate/HsOfficeSepaMandateControllerAcceptanceTest.java

@@ -138,7 +138,7 @@ class HsOfficeSepaMandateControllerAcceptanceTest extends ContextBasedTestWithCl
         void globalAdmin_canPostNewSepaMandate() {
 
             context.define("superuser-alex@hostsharing.net");
-            final var givenDebitor = debitorRepo.findDebitorByOptionalNameLike("Third").get(0);
+            final var givenDebitor = debitorRepo.findDebitorsByOptionalNameLike("Third").get(0);
             final var givenBankAccount = bankAccountRepo.findByIbanOrderByIbanAsc("DE02200505501015871393").get(0);
 
             final var location = RestAssured // @formatter:off
@@ -180,7 +180,7 @@ class HsOfficeSepaMandateControllerAcceptanceTest extends ContextBasedTestWithCl
         void globalAdmin_canNotPostNewSepaMandateWhenDebitorUuidIsMissing() {
 
             context.define("superuser-alex@hostsharing.net");
-            final var givenDebitor = debitorRepo.findDebitorByOptionalNameLike("Third").get(0);
+            final var givenDebitor = debitorRepo.findDebitorsByOptionalNameLike("Third").get(0);
             final var givenBankAccount = bankAccountRepo.findByIbanOrderByIbanAsc("DE02200505501015871393").get(0);
 
             final var location = RestAssured // @formatter:off
@@ -205,7 +205,7 @@ class HsOfficeSepaMandateControllerAcceptanceTest extends ContextBasedTestWithCl
         void globalAdmin_canNotPostNewSepaMandate_ifBankAccountDoesNotExist() {
 
             context.define("superuser-alex@hostsharing.net");
-            final var givenDebitor = debitorRepo.findDebitorByOptionalNameLike("Third").get(0);
+            final var givenDebitor = debitorRepo.findDebitorsByOptionalNameLike("Third").get(0);
             final var givenBankAccountUuid = UUID.fromString("00000000-0000-0000-0000-000000000000");
 
             final var location = RestAssured // @formatter:off
@@ -524,7 +524,7 @@ class HsOfficeSepaMandateControllerAcceptanceTest extends ContextBasedTestWithCl
     private HsOfficeSepaMandateEntity givenSomeTemporarySepaMandateForDebitorNumber(final int debitorNumber) {
         return jpaAttempt.transacted(() -> {
             context.define("superuser-alex@hostsharing.net");
-            final var givenDebitor = debitorRepo.findDebitorByDebitorNumber(debitorNumber).get(0);
+            final var givenDebitor = debitorRepo.findDebitorByDebitorNumber(debitorNumber).orElseThrow();
             final var bankAccountHolder = ofNullable(givenDebitor.getPartner().getPartnerRel().getHolder().getTradeName())
                     .orElse(givenDebitor.getPartner().getPartnerRel().getHolder().getFamilyName());
             final var givenBankAccount = bankAccountRepo.findByOptionalHolderLike(bankAccountHolder).get(0);

src/test/java/net/hostsharing/hsadminng/hs/office/sepamandate/HsOfficeSepaMandateRepositoryIntegrationTest.java

@@ -66,7 +66,7 @@ class HsOfficeSepaMandateRepositoryIntegrationTest extends ContextBasedTestWithC
             // given
             context("superuser-alex@hostsharing.net");
             final var count = sepaMandateRepo.count();
-            final var givenDebitor = debitorRepo.findDebitorByOptionalNameLike("First").get(0);
+            final var givenDebitor = debitorRepo.findDebitorsByOptionalNameLike("First").get(0);
             final var givenBankAccount = bankAccountRepo.findByOptionalHolderLike("Paul Winkler").get(0);
 
             // when
@@ -100,7 +100,7 @@ class HsOfficeSepaMandateRepositoryIntegrationTest extends ContextBasedTestWithC
 
             // when
             attempt(em, () -> {
-                final var givenDebitor = debitorRepo.findDebitorByOptionalNameLike("First").get(0);
+                final var givenDebitor = debitorRepo.findDebitorsByOptionalNameLike("First").get(0);
                 final var givenBankAccount = bankAccountRepo.findByOptionalHolderLike("Paul Winkler").get(0);
                 final var newSepaMandate = HsOfficeSepaMandateEntity.builder()
                         .debitor(givenDebitor)
@@ -397,7 +397,7 @@ class HsOfficeSepaMandateRepositoryIntegrationTest extends ContextBasedTestWithC
     private HsOfficeSepaMandateEntity givenSomeTemporarySepaMandate(final String iban) {
         return jpaAttempt.transacted(() -> {
             context("superuser-alex@hostsharing.net");
-            final var givenDebitor = debitorRepo.findDebitorByOptionalNameLike("First").get(0);
+            final var givenDebitor = debitorRepo.findDebitorsByOptionalNameLike("First").get(0);
             final var givenBankAccount = bankAccountRepo.findByIbanOrderByIbanAsc(iban).get(0);
             final var newSepaMandate = HsOfficeSepaMandateEntity.builder()
                     .debitor(givenDebitor)