Set null to target using mapstruct

Question

I am using mapstruct and I am wondering if there are any ways to set null value for some target properties. For example,

public class MySource {
    private String prop1;
    private String prop2;

    public MySource() {
        // Initialization.
    }

    // Getters - Setters.
}

public class MySourceDto {
    private String prop1;
    private String prop2;

    public MySourceDto() {
        // Initialization.
    }

    // Getters - Setters.
}

@Mapper
public interface MySourceMapper {

    @Mappings({
        @Mapping(target = "prop1", propertyToSetNull = null)})
    public MySourceDto toView(MySource mySource);

}

I would love the above source, dto and mapper to generate the below source code,

@Component
public class MySourceMapperImpl implements MySourceMapper {

    @Override
    public MySourceDto toView(MySource mySource) {
        if ( mySource == null ) {
            return null;
        }

        MySourceDto mySourceDto = new MySourceDto();

        mySourceDto.setProp1( mySource.getId() );
        mySourceDto.setProp2( null );

        return mySourceDto;
    }
}

Answer 1

You can use @Mapping(target = "prop1", expression = "java(null)") to achieve that.

You can find more information about expression in the reference guide here.

Currently only java is supported as an expression language, MapStruct will just take what you have written within the brackets and directly apply it to the setter, the implementation will look exactly like in your example.