Unmapped target property due to use of @AfterMapping

[Ben Wimpory]

Hi,

I am using a method with @AfterMapping annotation to map two "source" fields (a & b) from a DTO into a single field (x) on the target object.  This works.

Unfortunately due to a lack of @Mapping on the the two source fields (a&b) I get compilation warnings about these fields being unmapped.

Is my approach of using @AfterMapping on a custom method the right approach for doing a n->1 mapping ?

Thanks,

Ben

[Gunnar Morling]

Hi ben,

That warning is about unmapped *target* properties, so you should not see it about unmapped source fields. The rationale being that a mapping can be considered as a projection and it's legit to only have a subset of the source properties in a given target (e.g. for a view DTO), whereas an unpopulated property in the returned object is suspicious. 

Could you double check whether that's indeed about source properties? In that case could you provide a complete example exposing this issue?

>  Is my approach of using @AfterMapping on a custom method the right approach

You can do that, or go for an expression, which probably is less effort: @Mapping(target="x", expression="java(source.getA() + source.getB())"

Finally, You also can use @Mapping#ignore() and @Mapper#unmappedTargetPropertyPolicy() to get rid of the warning, but I'd double check first whether everything is doing what it should be doing.

--Gunnar

--Gunnar

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[Ben Wimpory]

Apologies for the delay getting back to you on this.

The error I am seeing from the example code below is about an unmapped target property.  This is created as I have only partially mapped the fields in the mapper, leaving the mapping of two source fields into one target field to an @AfterMapping.

:compileTestJava

...../src/test/java/mapstruct/InternalMapper.java:14: warning: Unmapped target property: "fullName".

    Internal internalFromDTO(DTO dto);

             ^

package mapstruct;

class DTO {
    private int age;
    private String first;
    private String last;

    public DTO(int age, String first, String last) {
        this.age = age;
        this.first = first;
        this.last = last;
    }

    public int getAge() {
        return age;
    }

    public String getFirst() {
        return first;
    }

    public String getLast() {
        return last;
    }
}

package mapstruct;

class Internal
{
    private int ageInYears;
    private String fullName;

    public Internal() {
    }

    public void setAgeInYears(int ageInYears) {
        this.ageInYears = ageInYears;
    }

    public void setFullName(String fullName) {
        this.fullName = fullName;
    }

    public int getAgeInYears() {
        return ageInYears;
    }

    public String getFullName() {
        return fullName;
    }
}

package mapstruct;

import org.mapstruct.Mapper;
import org.mapstruct.Mapping;
import org.mapstruct.Mappings;

@Mapper(uses = NameMapper.class)
public interface InternalMapper {
    @Mappings(
            {
                    @Mapping(source = "age", target = "ageInYears")
            }
    )
    Internal internalFromDTO(DTO dto);

}

package mapstruct;

import org.mapstruct.AfterMapping;
import org.mapstruct.Mapper;
import org.mapstruct.MappingTarget;

@Mapper
public abstract class NameMapper {
    @AfterMapping
    void after(DTO dto, @MappingTarget Internal internal)
    {
        internal.setFullName(String.format("%s, %s", dto.getLast(), dto.getFirst()));
    }
}

package mapstruct;

import org.junit.Test;
import org.mapstruct.factory.Mappers;

import static org.hamcrest.MatcherAssert.assertThat;
import static org.hamcrest.Matchers.is;

/**
 * Generates warning about unmapped target field, but have used @AfterMapping to set this field
 * .../src/test/java/mapstruct/InternalMapper.java:14: warning: Unmapped target property: "fullName".
 Internal internalFromDTO(DTO dto);
 ^
 */
public class UnusedSourceFieldsTests {

    @Test
    public void causesUnusedSourceFieldWarnings()
    {
        final InternalMapper mapper = Mappers.getMapper(InternalMapper.class);
        final DTO dto = new DTO(20, "Wish", "iWas");
        final Internal internal = mapper.internalFromDTO(dto);

        assertThat(internal.getFullName(), is("iWas, Wish"));
    }

}

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[Andreas Gudian]

Hi Ben,

You can acknowledge the warning by explicitly adding @Mapping(target="fullName", ignore = true).

Andreas

[Ben Wimpory]

Agreed this removes the warning.  Many thanks.

Is this the recommended way to map two fields to one ?

package mapstruct;

import org.mapstruct.Mapper;
import org.mapstruct.Mapping;
import org.mapstruct.Mappings;

@Mapper(uses = NameMapper.class)
public interface InternalMapper {
    @Mappings(
            {

                    @Mapping(source = "age", target = "ageInYears"),

                    @Mapping(target="fullName", ignore = true)
            }

    )
    Internal internalFromDTO(DTO dto);

}

[Andreas Gudian]

Yes. Either that or using the 'expression' attribute in the @Mapping annotation - but personally I would do it with @AfterMapping as well.

[Ben Wimpory]

Ok - thanks. Great library btw :-)