java mapstruct 1.3.1 ignore property in a list for bi-directional DTO mapping

Question

I'm struggling with cycle dependency problem with MapStruct. I keep having a StackOverFlow error due to circular dependencies. To avoid it, I just need to exclude a property of a List. I found this : https://github.com/mapstruct/mapstruct/issues/933 I deeply looked over the internet and I have been surprised that I couldn't find any full exemple showing a bi-directional DTO mapping with MapStruct (except using @Context CycleAvoidingMappingContext, not working to me).

[EDIT]: I found a workaround thanks to MapStruct chat, I add it to EditorMapper

Here is my case, pretty common I guess : I have 2 DTOs referencing each other:

public class BookDTO {

    private Long id;

    private String title;

        //... other properties

    //@JsonManagedReference --> not necessary anymore
    private EditorDTO editor;
}

public class EditorDTO {

    private Long id;
    private String name;

        //...other properties

    //@JsonBackReference --> not necessary anymore
    private List< BookDTO > bookList;
}

And I need MapStruct to be able to exclude the property Editor from the BookList in Editor, and then avoid the infinite loop. Here is what I currently have as mappers:

@Mapper
public interface BookMapper {

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

    @Mapping( target = "editor.bookList", ignore = true)
    BookDTO toDTO( BookEntity bookEntity );

    @Named( "NoEditor" )
    @Mapping(target = "editor", ignore = true)
    BookDTO toDTONoEditor( BookEntity bookEntity );

    List<BookDTO> toDTOList( List<BookEntity> bookEntityList );

    @Named( "NoEditor" )
    @IterableMapping(qualifiedByName="NoEditor")
    List<BookDTO> toDTOListNoEditor( List<BookEntity> bookEntityList );

    @Mapping( target = "editor.bookList", ignore = true)
    BookEntity toEntity( BookDTO bookDTO );

    List<BookEntity> toEntityList( List<BookDTO> bookDTOList );
}

@Mapper(uses = BookMapper.class)
public interface EditorMapper {

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

    @Named( "NoEditor" )
    @Mapping(target = "bookList", qualifiedByName = "NoEditor")
    EditorDTO toDTO( EditorEntity editorEntity );

    @Named( "NoEditor" )
    @IterableMapping(qualifiedByName="NoEditor")
    List<EditorDTO> toDTOList( List< EditorEntity > editorEntityList );

    EditorEntity toEntity( EditorDTO editorDTO );

    List<EditorEntity> toEntityList( List< EditorDTO > editorDTOList );
}

[EDIT]: it now works but it's not 100% clean (please see the answer I posted for more details)

I also tried this kind of method in mappers, but it didn't have any effect on my pb.

BookDTO toDTO( BookEntity bookEntity, @Context CycleAvoidingMappingContext context );

Does anyone know what I'm doing wrong? THANKS A LOT! :)

Answer 1

[EDIT]: I add the solution for a bi-directional ManyToMany mapping too Thanks to https://gitter.im/mapstruct/mapstruct-users#, I have been able to get the solution. [EDIT]: I still had errors that I didn't realize. It's now corrected in this update. I had to : - add uses attribut to EditorMapper: @Mapper(componentModel = "spring", uses = BookMapper.class) - add alternatives methods like toDTONoEditor or toDTOListNoEditor in BookMapper where I ignore the editor property. - map theses alternative methods in EditorMapper - same for each circular dependency

Here is the solution:

BookDTO

public class BookDTO {

    private Long id;

    private String title;

        //... other properties

    private EditorDTO editor;
    private List< CategoryDTO > categoryList;
}

EditorDTO

public class EditorDTO {

    private Long id;
    private String name;

        //...other properties

    private List< BookDTO > bookList;
}

CategoryDTO

public class CategoryDTO {

    private Long id;

    private String category;

    private List< BookDTO > bookList;
}

BookMapper

@Mapper(componentModel = "spring", uses = {CategoryMapper.class, EditorMapper.class})
public interface BookMapper {


    @Named( "NoBook" )
    @Mappings( {
            @Mapping(target = "categoryList", qualifiedByName = "NoBook"),
            @Mapping( target = "editor.bookList", ignore = true)
    } )
    BookDTO toDTO( BookEntity bookEntity );

    @Named( "NoEditor" )
    @Mappings( {
            @Mapping(target = "editor", ignore = true),
            @Mapping(target = "categoryList", qualifiedByName = "NoBook")
    } )
    BookDTO toDTONoEditor( BookEntity bookEntity );

    @Named( "NoCategory" )
    @Mappings( {
            @Mapping(target = "categoryList", ignore = true),
            @Mapping(target = "editor", qualifiedByName = "NoBook")
    } )
    BookDTO toDTONoCategory( BookEntity bookEntity );


    @Named( "NoBook" )
    @IterableMapping(qualifiedByName="NoBook")
    List<BookDTO> toDTOList( List<BookEntity> bookEntityList );

    @Named( "NoEditor" )
    @IterableMapping(qualifiedByName="NoEditor")
    List<BookDTO> toDTOListNoEditor( List<BookEntity> bookEntityList );

    @Named( "NoCategory" )
    @IterableMapping(qualifiedByName="NoCategory")
    List<BookDTO> toDTOListNoCategory( List<BookEntity> bookEntityList );


    @Named( "NoBook" )
    @Mappings( {
            @Mapping(target = "categoryList", qualifiedByName = "NoBook"),
            @Mapping( target = "editor.bookList", ignore = true)
    } )
    BookEntity toEntity( BookDTO bookDTO );

    @Named( "NoCategory" )
    @Mapping(target = "categoryList", ignore = true)
    BookEntity toEntityNoCategory( BookDTO bookDTO );


    @Named( "NoBook" )
    @IterableMapping(qualifiedByName="NoBook")
    List<BookEntity> toEntityList( List<BookDTO> bookDTOList );

    @Named( "NoCategory" )
    @IterableMapping(qualifiedByName="NoCategory")
    List<BookEntity> toEntityListNoCategory( List<BookDTO> bookDTOList );
}

EditorMapper

@Mapper(componentModel = "spring", uses = BookMapper.class)
public interface EditorMapper {

    @Named( "NoEditor" )
    @Mapping(target = "bookList", qualifiedByName = "NoEditor")
    EditorDTO toDTO( EditorEntity editorEntity );

    @Named( "NoBook" )
    @Mapping(target = "bookList", ignore = true)
    EditorDTO toDTONoBook( EditorEntity editorEntity );


    @Named( "NoEditor" )
    @IterableMapping(qualifiedByName="NoEditor")
    List< EditorDTO > toDTOList( List< EditorEntity > editorEntityList );

    @Named( "NoBook" )
    @IterableMapping(qualifiedByName="NoBook")
    List< EditorDTO > toDTOListNoBook( List< EditorEntity > editorEntityList );

    @Named( "NoBook" )
    @Mapping(target = "bookList", qualifiedByName = "NoBook")
    EditorEntity toEntity( EditorDTO editorDTO );

    @Named( "NoBook" )
    @IterableMapping(qualifiedByName="NoBook")
    List< EditorEntity > toEntityList( List< EditorDTO > editorDTOList );
}

CategoryMapper

@Mapper(componentModel = "spring",uses = BookMapper.class)
public interface CategoryMapper {


    @Named( "NoCategory" )
    @Mapping(target = "bookList", qualifiedByName = "NoCategory")
    CategoryDTO toDTO( CategoryEntity categoryEntity );

    @Named( "NoBook" )
    @Mapping(target = "bookList", ignore = true)
    CategoryDTO toDTONoBook( CategoryEntity categoryEntity );


    @Named( "NoCategory" )
    @IterableMapping(qualifiedByName="NoCategory")
    List<CategoryDTO> toDTOList( List< CategoryEntity > categoryEntityList );

    @Named( "NoBook" )
    @IterableMapping(qualifiedByName="NoBook")
    List<CategoryDTO> toDTOListNoBook( List< CategoryEntity > categoryEntityList );


    @Named( "NoCategory" )
    @Mapping(target = "bookList", qualifiedByName = "NoCategory")
    CategoryEntity toEntity( CategoryDTO categoryDTO );

    @Named( "NoBook" )
    @Mapping(target = "bookList", ignore = true)
    CategoryEntity toEntityNoBook( CategoryDTO categoryDTO );


    @Named( "NoCategory" )
    @IterableMapping(qualifiedByName="NoCategory")
    List<CategoryEntity> toEntityList( List< CategoryDTO > categoryDTOList );

    @Named( "NoBook" )
    @IterableMapping(qualifiedByName="NoBook")
    List<CategoryEntity> toEntityListNoBook( List< CategoryDTO > categoryDTOList );

}

This way, The circular dependency is broken before it comes to infinite loop. However, it is 99% satisfying, because the Editor and Book objects aren't perfectly clean. Editor contains the bookList, well. But each book in bookList still contains a null editor field. And vice versa for the Book object. But it seems to be a De/Serialization problem, not a MapStruct one. Here are the Json resulting

Editor

{
  "id": 1,
  "name": "Folio",
  "coordinates": null,
  "bookList": [
    {
      "id": 1,
      "title": "Le cycle de Fondation, I : Fondation",
      "categoryList": [
        {
          "id": 5,
          "category": "LITERATURE&FICTION"
        }
      ],
      "language": "French",
      "isbn": 2070360539,
      "publicationDate": null,
      "numberOfPages": 416,
      "authorList": [],
      "libraryList": [
        {
          "id": 2,
          "name": "Library2",
          "coordinates": null
        },
        {
          "id": 1,
          "name": "Library1",
          "coordinates": null
        }
      ],
      "editor": null
    }
  ]
}

Book

{
  "id": 1,
  "title": "Le cycle de Fondation, I : Fondation",
  "categoryList": [
    {
      "id": 5,
      "category": "LITERATURE&FICTION",
      "bookList": null
    }
  ],
  "language": "French",
  "isbn": 2070360539,
  "publicationDate": null,
  "numberOfPages": 416,
  "authorList": [],
  "libraryList": [
    {
      "id": 2,
      "name": "Library2",
      "coordinates": null
    },
    {
      "id": 1,
      "name": "Library1",
      "coordinates": null
    }
  ],
  "editor": {
    "id": 1,
    "name": "Folio",
    "coordinates": null,
    "bookList": null
  }
}

Category

{
  "id": 1,
  "category": "CHILDREN",
  "bookList": [
    {
      "id": 5,
      "title": "Le petit prince",
      "categoryList": null,
      "language": "French",
      "isbn": 9782070612758,
      "publicationDate": null,
      "numberOfPages": 120,
      "authorList": [],
      "libraryList": [
        {
          "id": 2,
          "name": "Library2",
          "coordinates": null
        },
        {
          "id": 1,
          "name": "Library1",
          "coordinates": null
        }
      ],
      "editor": null
    }
  ]
}

Hope this help :)