How to get element of List in target(for mapping) if source doesn't contain this list?

Question

I'm trying to map next structure(succesfully map in dozer, have some problems with mapstruct) list is absent in source, how can I get its first element in mapper? Target class:

    @Data
public class FirstLvl {
        protected List<SecondLvl> list;
        
        @Data
        public static class SecondLvl {
                protected FirstLvl.SecondLvl.ThirdLvl thirdLvl;

                @Data
                public static class ThirdLvl {
                        protected FourthLvl fourthLvl;
                }
        }
}

@Data
public class FourthLvl {
        protected FourthLvl.FithLvl fithLvl;

        @Data
        public static class FithLvl {

                protected String str1;
                protected String str2;

        }
}

Source:

@Data
public class FirstLvlDTO {
      protected FirstLvlDTO.SecondLvlDTO secondLvlDTO ;

        @Data
        public static class SecondLvlDTO  {
            protected FirstLvlDTO.SecondLvlDTO.ThirdLvlDTO thirdLvlDTO ;


                @Data
                public static class ThirdLvlDTO {

                        protected FourthLvlDTO fourthLvlDTO;
                }
        }

}

@Data
public class FourthLvlDTO  {

        protected String str1;

        protected String str2;

}

Mapper and Object factory:

@Mapper(uses = { ObjectFactory.class })
public interface FirstLvlDTOtoFirstLvl  {

@Mapping(target="list[0].thirdLvl.fourthLvl.fithLvl.str2", source="secondLvlDTO.thirdLvlDTO.fourthLvlDTO.str2")

    FirstLvl toFirstLvl (FirstLvlDTO firstLvlDTO );
        
}

public class ObjectFactory {

    public FirstLvl createFirstLvl() {
        return new FirstLvl();
    }
    
    public FirstLvl.SecondLvl createFSLvl() {
        return new FirstLvl.SecondLvl();
    }
}

The problem is I don't know how to get first element of List([] notation is not used in mapstruct). I can add methods getlist0/setlist0 to class FirstLvl for simply returning first element of List(return list.get(0)) and use it in mapper like list0.thirdLvl.fourthLvl.fithLvl.str2, but I don't know is it good idea and is it possible to do it better List is absent in FirstLvlDTO (source), so I really can't understand how to map it and set this nested structure to first element of List

Answer 1

I am not sure that i completly understand your Code. My approach would look something like this. However your types in the list seem not to match.

public interface TestMapper {

    @Mapping(target = "list0", ignore = true)
    @Mapping(target = "list", ignore = true)
    A toA(A1 a1);

    @AfterMapping
    default void mapperCode(@MappingTarget A a, A1 a1) {
        List<A.B> list = a.getList(); // target list requiures Type A.B 
        A1.B1 b1 = a1.getB1(); // source does have A1.B1 and not A.B as type
        // if your Types match set the list here manually like 
        // a.setList(List.of(a1.getB()));
    }

}

Your code is har dto read using only A,B,A1,B1,... . I Would suggest you use real names.

EDIT:

a Working but really ugly solution would be doing it manually. I am not sure if that helps you.

public interface TestMapper {

@Mapping(target = "list", ignore = true)
FirstLvl map(FirstLvlDTO firstLvlDTO);

@AfterMapping
default void mapperCode(@MappingTarget FirstLvl firstLvl, FirstLvlDTO firstLvlDTO) {
    String str1 = firstLvlDTO.getSecondLvlDTO().getThirdLvlDTO().getFourthLvlDTO().getStr1();
    String str2 = firstLvlDTO.getSecondLvlDTO().getThirdLvlDTO().getFourthLvlDTO().getStr2();
    FirstLvl.SecondLvl secondLvl = new FirstLvl.SecondLvl();
    FirstLvl.SecondLvl.ThirdLvl thirdLvl = new FirstLvl.SecondLvl.ThirdLvl();
    secondLvl.setThirdLvl(thirdLvl);
    FourthLvl fourthLvl = new FourthLvl();
    thirdLvl.setFourthLvl(fourthLvl);
    FourthLvl.FithLvl fithLvl = new FourthLvl.FithLvl(str1, str2);
    fourthLvl.setFithLvl(fithLvl);
    firstLvl.setList(Arrays.asList(secondLvl));
}

}

@Data
public class FourthLvl {
protected FourthLvl.FithLvl fithLvl;

@Data
public static class FithLvl {

    public FithLvl(String str1, String str2){
        this.str1 = str1;
        this.str2 = str2;
    }

    protected String str1;
    protected String str2;

}

}

Answer 2

Mapstruct does not support many-to-one or one-to-many mappings, these need to be manually implemented.

here you find a working example for your classes:

@Mapper
public abstract class LevelMapper {

    @Mapping( target = "secondLvlDTO", source = "list" )
    public abstract FirstLvlDTO map(FirstLvl lvl);

    // used by the manual implementation to continue mapping.
    @Mapping( target = "thirdLvlDTO.fourthLvlDTO", source = "thirdLvl.fourthLvl.fithLvl" )
    protected abstract SecondLvlDTO map(SecondLvl lvl);

    // manually implementation for getting the first object from the list and converting it.
    protected SecondLvlDTO getFirst(List<SecondLvl> list) {
        return map( list.get( 0 ) );
    }

// the reverse
    
    @Mapping( target = "list", source = "secondLvlDTO" )
    public abstract FirstLvl map(FirstLvlDTO lvl);

    // used by the manual implementation to continue mapping.
    @Mapping( target = "thirdLvl.fourthLvl.fithLvl", source = "thirdLvlDTO.fourthLvlDTO" )
    protected abstract SecondLvl map(SecondLvlDTO lvl);

    // manually implementation for creating the the list and filling it with the converted dto.
    protected List<SecondLvl> asList(SecondLvlDTO dto) {
        return Arrays.asList( map( dto ) ); // or any other way to create a list.
    }
}