mapstruct如何将实体映射到字符串，并将字符串映射到相应的实体

Question

我有下面的结构，我想用MapStruct映射这个。

class DTO
{
  private Integer id;
  String comment;
  //getters & setters
}

class ParentEntity
{
  private Integer id;
  CommentEntity comment;
  //getters & setters
}

class CommentEntity
{
  private Integer id;
  private String text;
  //getters & setters
}

@Mapper(componentModel = "spring")
public interface SampleMapper
{
    @Mapping(source = "entity.comment.text", target = "comment")
    public DTO toDTO(final ParentEntity entity);

    @Mapping(source = "dto.comment", target = "comment.text")
    public ParentEntity toEntity(final DTO dto);
}

下面是mapstruct为toDTO方法生成的实现

@Override
public DTO toDTO(ParentEntity entity) {
    if ( entity == null ) {
        return null;
    }    
    DTO dto = new DTO();
    dto.setComment( entityCommentText( entity ) );
    ....................
}

private String entityCommentText(ParentEntity entity) {
    if ( entity == null ) {
        return null;
    }
    Comment comment = entity.getComment();
    if ( comment == null ) {
        return null;
    }
    String text = comment.getText();
    if ( text == null ) {
        return null;
    }
    return text;
}

下面是mapstruct为toEntity方法生成的实现

@Override
public ParentEntity toEntity(DTO dto) {
    if ( dto == null ) {
        return null;
    }

    ParentEntity entity = new ParentEntity();

    entity.setComment( dtoToCommentEntity( dto ) );
    .............
}

protected CommentEntity dtoToCommentEntity(DTO dto) {
    if ( dto == null ) {
        return null;
    }

    CommentEntity commentEntity = new CommentEntity();

    commentEntity.setText( dto.getComment() );

    return commentEntity;
}

我的问题是Todto()方法只在文本不为空时设置注释。但是toentity()方法不检查空文本或空文本。因此，如果我在DTO中获得“comment”:null，它将创建一个新的comment对象并将文本设置为null。如何避免这一点？有人能解释一下这种行为并建议我正确的做法吗？谢了！

Answer 1

像这样：

@Mapper(  componentModel = "spring" )
public interface MyMapper {

    @Mapping(source = "entity.comment.text", target = "comment")
    DTO toDTO(final ParentEntity entity);

    // make sure the entire parameter dto is mapped to comment
    @Mapping(source = "dto", target = "comment")
    ParentEntity toEntity(final DTO dto);

    // and MapStruct will select your own implementation
    default CommentEntity dTOToCommentEntity(DTO dTO) {
        if ( dTO == null ) {
            return null;
        }

        CommentEntity commentEntity = null;
        if (  dTO.getComment()!= null  ) {
            commentEntity = new CommentEntity();
            commentEntity.setText( dTO.getComment() );
        }
        return commentEntity;
    }
}