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#2687 Add documentation for NullValueMappingStrategy for collections and maps

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Filip Hrisafov 2021-12-25 13:12:29 +01:00
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documentation/src/main/asciidoc/chapter-10-advanced-mapping-options.asciidoc
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@ -212,6 +212,29 @@ However, by specifying `nullValueMappingStrategy = NullValueMappingStrategy.RETU
The strategy works in a hierarchical fashion. Setting `nullValueMappingStrategy` on mapping method level will override `@Mapper#nullValueMappingStrategy`, and `@Mapper#nullValueMappingStrategy` will override `@MapperConfig#nullValueMappingStrategy`.
[[mapping-result-for-null-collection-or-map-arguments]]
=== Controlling mapping result for 'null' collection or map arguments
With <<mapping-result-for-null-arguments>> it is possible to control how the return type should be constructed when the source argument of the mapping method is `null`.
That is applied for all mapping methods (bean, iterable or map mapping methods).
However, MapStruct also offers a more dedicated way to control how collections / maps should be mapped.
e.g. return default (empty) collections / maps, but return `null` for beans.
For collections (iterables) this can be controlled through:
* `MapperConfig#nullValueIterableMappingStrategy`
* `Mapper#nullValueIterableMappingStrategy`
* `IterableMapping#nullValueMappingStrategy`
For maps this can be controlled through:
* `MapperConfig#nullValueMapMappingStrategy`
* `Mapper#nullValueMapMappingStrategy`
* `MapMapping#nullValueMappingStrategy`
How the value of the `NullValueMappingStrategy` is applied is the same as in <<mapping-result-for-null-arguments>>
[[mapping-result-for-null-properties]]
=== Controlling mapping result for 'null' properties in bean mappings (update mapping methods only).