109 lines
2.8 KiB
Markdown
109 lines
2.8 KiB
Markdown
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# Object Mapping
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**Status:**
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- [x] proposed by Michael Hönnig
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- [ ] accepted by (Participants)
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- [ ] rejected by (Participants)
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- [ ] superseded by (superseding ADR)
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## Context and Problem Statement
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Since we are using the *API first*-approach,
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thus generating Java interfaces and model classes from an OpenAPI specification,
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we cannot use the JPA-entities anymore at the API level,
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not even if the data fields are 100% identical.
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Therefore, we need some kind of mapping strategy.
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### Technical Background
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Java does not support duck-typing and therefore, objects of different classes have to be converted to each other, even if all data fields are identical.
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In our case, the database query is usually the slowest part of handling a request.
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Therefore, for the mapper, ease of use is more important than performance,
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at least as long as the mapping part does not take more than 10% of the total request.
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## Considered Options
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* specific programmatic conversion
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* using the *MapStruct* library
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* using the *ModelMapper* library
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* Dozer, last update from 2014 + vulnerabilities => skipped
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* Orika, last update from 2019 + vulnerabilities => skipped
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* JMapper
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### specific programmatic conversion
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In this solution, we would write own code to convert the objects.
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This usually means 3 converters for each entity/resource pair:
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- entity -> resource
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- resource -> entity
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- list of entities -> list of resources
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#### Advantages
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Very flexible and fast.
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#### Disadvantages
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Huge amounts of bloat code.
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### using the *MapStruct* library
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See https://mapstruct.org/.
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#### Advantages
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- Most popular mapping library in the Java-world.
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- Actively maintained, last release 1.5.2 from Jun 18, 2022.
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- very fast (see [^1])
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#### Disadvantages
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- Needs interface declarations with annotations.
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- Looks like it causes still too much bloat code for our purposes.
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### using the *ModelMapper* library
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See http://modelmapper.org/.
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#### Advantages
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- 1:1 mappings just need a simple method call without any bloat-code.
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- Actively maintained, last release 3.1.0 from Mar 08, 2022.
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#### Disadvantages
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- could not find any, will give it a try
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### using the *JMapper* library
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See https://jmapper-framework.github.io/jmapper-core/.
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#### Advantages
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- Supports annotation-based and programmatic mapping exceptions.
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- Actively maintained, last release 1.6.3 from May 27, 2022.
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- very fast (see [^1])
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#### Disadvantages
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- needs a separate mapper instance for each mapping pair
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- cannot map collections (needs `stream().map(...).collect(toList())` or similar)
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## Decision Outcome
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We chose the option **"using the *ModelMapper* library"** because it has an acceptable performance without any bloat code.
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If it turns out to be too slow after all, "using the *JMapper* library" seems to be a good alternative.
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[^1]: https://www.baeldung.com/java-performance-mapping-frameworks
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