MapStruct - custom mapping of target field based on 2 or more different source objects

Question

I am trying to figure out how to implement the following mapping:

class SuperComplexClass {
    Long value;
    String description;
}

class MapIntoMe {
    
    // Many other fields that is also mapped
    
    SuperComplexClass superComplexObject;
}

class MapFromMe {
    ComplexClassPart1 complexClassPart;
}

class AdditionalData {
    ComplexClassPart2 complexClassPart;
}


@Mapper
public interface SomeFancyMapper {

    @Mapping(target = "superComplexObject", source = "{mfm.complexPart, ad.complexPart}",
             qualifiedByName = "mapSuperComplexObject")
    MapIntoMe mapFromMeIntoMe(MapFromMe mfm, AdditionalData ad);
    

    @Named("mapSuperComplexObject")
    default SuperComplexClass mapSuperComplexObject(ComplexPart1 p1, ComplexPart2 p2) {
        SuperComplexClass superObject = new SuperComplexClass();
        //some logic that calculates and fills superObject]
        return superObject;
    }
}

And now obviously expression like source = "{mfm.complexPart, ad.complexPart}" is not working, but it shows clearly what I would like to achieve.

So far I wasn't able to find the answer if that's possible with this approach and without some ugly workarounds.

Any ideas?

Answer 1

Currently it is not supported to reuse mapping methods with more than one parameter. That is why something like the expression you shared doesn't work.

However, you could use expression, @AfterMapping or @Context (in case you don't need to use AdditionalData for other mapping) to achieve what you need.

Using Expression

@Mapper
public interface SomeFancyMapper {

    @Mapping(target = "superComplexObject", expression = "java(mapSuperComplexObject(mfm.getComplexPart(), ad.getComplexPart()))")
    MapIntoMe mapFromMeIntoMe(MapFromMe mfm, AdditionalData ad);
    

    default SuperComplexClass mapSuperComplexObject(ComplexPart1 p1, ComplexPart2 p2) {
        SuperComplexClass superObject = new SuperComplexClass();
        //some logic that calculates and fills superObject]
        return superObject;
    }
}

Using @AfterMapping

@Mapper
public interface SomeFancyMapper {

    @Mapping(target = "superComplexObject", ignore = true)
    MapIntoMe mapFromMeIntoMe(MapFromMe mfm, AdditionalData ad);
    
    @AfterMapping
    default void mapSuperComplexObject(@MappingTarget MapIntoMe target, MapFromMe mfm, AdditionalData ad) {

        SuperComplexClass superObject = new SuperComplexClass();
        //some logic that calculates and fills superObject]
        return superObject;
    }
}

Using @Context

@Mapper
public interface SomeFancyMapper {

    @Mapping(target = "superComplexObject", source = "complexPart",
             qualifiedByName = "mapSuperComplexObject")
    MapIntoMe mapFromMeIntoMe(MapFromMe mfm, @Context AdditionalData ad);
    

    @Named("mapSuperComplexObject")
    default SuperComplexClass mapSuperComplexObject(ComplexPart1 p1, @Context AdditionalData ad) {
        SuperComplexClass superObject = new SuperComplexClass();
        //some logic that calculates and fills superObject]
        return superObject;
    }
}

Keep in mind that when using @Context the parameter annotated with that annotation cannot be used in Mapping#target. It is an additional context that can be passed to other mapping methods or lifecycle methods.