defaultExpression not being applied when source property not specified explicitly

[marceloverdijk]

When having the following classes:

public class AnimalRecord {

    private String[] previousNames;
}

public class Animal {

    private List<String> previousNames;
}

and a mapper like:

@Mapper
public interface AnimalRecordMapper {

    @Mapping(target = "previousNames", 
            nullValueCheckStrategy = NullValueCheckStrategy.ALWAYS, 
            defaultExpression = "java(Collections.emptyList())")
    Animal toAnimal(AnimalRecord record);
}

I would expect that the implementation would convert a null array in AnimalRecord to an empty List (not null) in the Animal instance.

However the generated code looks like:

@Override
public Animal toAnimal(AnimalRecord record) {
    if ( record == null ) {
        return null;
    }

    Animal animal = new Animal();

    List<String> list = stringArrayToStringList( record.getPreviousNames() );
    if ( list != null ) {
        animal.setPreviousNames( list );
    }

    return animal;
}

When I explicitly add the source = "previousNames" to the @Mapping like:

@Mapper
public interface AnimalRecordMapper {

    @Mapping(source = "previousNames", 
            target = "previousNames", 
            nullValueCheckStrategy = NullValueCheckStrategy.ALWAYS, 
            defaultExpression = "java(Collections.emptyList())")
    Animal toAnimal(AnimalRecord record);
}

then the code is generated as expected:

@Override
public Animal toAnimal(AnimalRecord record) {
    if ( record == null ) {
        return null;
    }

    Animal animal = new Animal();

    List<String> list = stringArrayToStringList( record.getPreviousNames() );
    if ( list != null ) {
        animal.setPreviousNames( list );
    }
    else {
        animal.setPreviousNames( Collections.emptyList() );
    }

    return animal;
}

Note the else part generated to set the empty list.

It seems the defaultExpression is not being applied when the source property is not specified.
Maybe in general or related to the fact that there is also an array to List conversion needed.

[marceloverdijk]

Note: using MapStruct 1.3.1.Final.

[filiphr]

Thanks for the issue @marceloverdijk. In my opinion this is a bug, we should always apply the defaultExpression irregardless whether source is defined or not. Since it applies to the target property

[sjaakd]

@marceloverdijk .. I tried to replicate the problem, but.. it works on my machine 😄

@Mapper( imports = Collections.class )
public interface Issue1966Mapper {

    Issue1966Mapper INSTANCE = Mappers.getMapper(Issue1966Mapper.class);

    @Mapping(target = "previousNames",
        nullValueCheckStrategy = NullValueCheckStrategy.ALWAYS,
        defaultExpression = "java(Collections.emptyList())")
    Animal toAnimal(AnimalRecord record);

    class AnimalRecord {

         private String[] previousNames;

        public String[] getPreviousNames() {
            return previousNames;
        }

        public void setPreviousNames(String[] previousNames) {
            this.previousNames = previousNames;
        }
    }

    class Animal {

        private List<String> previousNames;

        public List<String> getPreviousNames() {
            return previousNames;
        }

        public void setPreviousNames(List<String> previousNames) {
            this.previousNames = previousNames;
        }
    }

}

result (as expected):

@Generated(
    value = "org.mapstruct.ap.MappingProcessor",
    date = "2019-11-10T12:25:37+0100",
    comments = "version: , compiler: Eclipse JDT (Batch) 1.2.100.v20160418-1457, environment: Java 1.8.0_181 (Oracle Corporation)"
)
public class Issue1966MapperImpl implements Issue1966Mapper {

    @Override
    public Animal toAnimal(AnimalRecord record) {
        if ( record == null ) {
            return null;
        }

        Animal animal = new Animal();

        List<String> list = stringArrayToStringList( record.getPreviousNames() );
        if ( list != null ) {
            animal.setPreviousNames( list );
        }
        else {
            animal.setPreviousNames( Collections.emptyList() );
        }

        return animal;
    }

    protected List<String> stringArrayToStringList(String[] stringArray) {
        if ( stringArray == null ) {
            return null;
        }

        List<String> list = new ArrayList<String>( stringArray.length );
        for ( String string : stringArray ) {
            list.add( string );
        }

        return list;
    }
}

Note: I used the latest master branch in order to create a test case. But I don't think we fixed an issue in this area.

Note ii: I added an import to my mapper.

[marceloverdijk]

Interesting @sjaakd :-)

I've setup this sample project https://github.com/marceloverdijk/mapstruct-1966
It contains a failing tests, when adding the source property explicitly the test succeeds.

Could you check it out and see if you see different behavior?

[sjaakd]

I just checked.. Compile your example against 1.4.0-SNAPSHOT (our master) and it works as expected.. I guess we must have fixed something for the better 😄

[sjaakd]

I added #1967 jus to avoid regression.

[sjaakd]

@marceloverdijk thanks for reporting. I'll proceed to close the issue, since the problem does not occur on our master.

[marceloverdijk]

Yes, I can confirm with 1.4.0-SNAPSHOT it works as expected 👍

[shamoh]

When do you expect the 1.4.0 is going to be released?

[rdolejsi]

Hello, I'm trying the same use case and hitting the bug as well. Tried 1.4.2.Final, 1.5.0.Beta1 and 1.5.0.RC1.

In my case an object has List where Step -> StepRecord is also processed by the mapper. The mapping looks like this:
@Mapping(target = "steps", source = "steps", defaultExpression = "java( new ArrayList<>() )"),

The generated code calls a separate method:
parentRecord.steps( StepListToStepRecordList( dto.getSteps() ) )

And the method starts with the following statement:

if ( list == null ) {
    return null;
}

After checking the rest of the generated mapper, the defaultExpression code is actually present, but just in the update() logic, not in to(). Is there any way to process default values during standard conversion or do we need to always call to() and then update() to make sure the defaults are applied?