MapStruct: Map List of objects, when object is mapped from two objects

Question

Assume I have such mapping:

@Mapping(source = "parentId", target = "parent.id")
Child map(ChildDto dto, Parent parent);

Now I need to map List of ChildDto to List of Child, but they all have the same parent. I expect to do something like that:

List<Child> map(List<ChildDto> dtoList, Parent parent);

But it doesn't working. Is there any chance to do it?

Answer 1

I found how to implement it with decorators, thanks @Gunnar Here is an implementation:

Beans

public class Child {
    int id;
    String name;
}
public class Parent {
    int id;
    String name;
}
public class ChildDto {
    int id;
    String name;
    int parentId;
    String parentName;
}
// getters/settes ommited

Mapper

@Mapper
@DecoratedWith(ChildMapperDecorator.class)
public abstract class ChildMapper {
    public static final ChildMapper INSTANCE = Mappers.getMapper(ChildMapper.class);

    @Mappings({
            @Mapping(target = "parentId", ignore = true),
            @Mapping(target = "parentName", ignore = true)
    })
    @Named("toDto")
    abstract ChildDto map(Child child);

    @Mappings({
            @Mapping(target = "id", ignore = true),
            @Mapping(target = "name", ignore = true),
            @Mapping(target = "parentId", source = "id"),
            @Mapping(target = "parentName", source = "name")
    })
    abstract ChildDto map(@MappingTarget ChildDto dto, Parent parent);

    @IterableMapping(qualifiedByName = "toDto") // won't work without it
    abstract List<ChildDto> map(List<Child> children);

    List<ChildDto> map(List<Child> children, Parent parent) {
        throw new UnsupportedOperationException("Not implemented");
    }
}

Decorator

public abstract class ChildMapperDecorator extends ChildMapper {
    private final ChildMapper delegate;

    protected ChildMapperDecorator(ChildMapper delegate) {
        this.delegate = delegate;
    }

    @Override
    public List<ChildDto> map(List<Child> children, Parent parent) {
        List<ChildDto> dtoList = delegate.map(children);
        for (ChildDto childDto : dtoList) {
            delegate.map(childDto, parent);
        }
        return dtoList;
    }
}

I use abstract class, not interface for mapper, because in case of interface you couldn't exclude for generation method map(List<Child> children, Parent parent), and the code being generated is not valid in compile time.