How to exclude a field when its id is empty in mapStruct?

Question

i am new at mapStruct and i don't know how to exclude a field when it's empty.

The Classes look like these:

public class MyClass {
    String reference;
    Info info;
    ...
}

public class Info{
    Long id;
    List<String> parts = new ArrayList<>();
    ...
}

And this is the mapper:

@Mapping(target = "info.id", source = "infoId")
public abstract MyClass toMyClass(RequestProto.line Line);

So when the info.id comes empty i get MyClass instantiated with the parameter info with an empty list of parts.

MYCLASS(current)
{
    reference: "aa",
     info: {
       parts: []
     }  
}

What i want is that when the info.id is empty the info parameter is null.

MYCLASS(expected)
{
    reference: "aa" 
    info: null
}

I have no idea how to achieve this.

I hope i explained my self. If someone can bring me some light with this would be much appreciated

Answer 1

You could use your own logic for it:

@Mapping(target = "info", source = "Line", qualifiedByName = "info")
public abstract MyClass toMyClass(RequestProto.line Line);

@Named("info")
public Info mapInfo(RequestProto.line Line) {
   if(infoId.isEmpty()) {
      return null;
   }
   Info info = new Info();
   info.setId(infoId);
   return info;
}

or you could create new class for it:

@Mapper(uses = {InfoMapper.class}, unmappedTargetPolicy = ReportingPolicy.IGNORE)
public MyClassMapper {

   @Mapping(target = "info", source = "Line", qualifiedByName = "info")
   public abstract MyClass toMyClass(RequestProto.line Line);
}
public class InfoMapper implements Function<Info, RequestProto.line> {

   @Override
   @Named("info")
   public Info apply(RequestProto.line Line) {
   //pseudo code, make it better based on your request object
      if(infoId.isEmpty()) {
          return null;
      }
      Info info = new Info();
      info.setId(infoId);
      return info;
   }