Mapstruct, service, controller - Send nested entity having (many-to-one relation) in the request

[svetlana ilina]

Hello everyone,

I have 2 entities Answer and Question with many-to-one relation as given below.

package com.example.demo.models.entitys;

import jakarta.persistence.*;
import lombok.AllArgsConstructor;
import lombok.Getter;
import lombok.NoArgsConstructor;
import lombok.Setter;

@Entity
@Table(name = "questions")
@Getter
@Setter
@NoArgsConstructor
@AllArgsConstructor
public class Question {

    @Id
    @GeneratedValue(strategy = GenerationType.SEQUENCE)
    private Long id;

    private String question;

    @Column(name = "position")
    private Integer position;
}



import java.util.Objects;

@Builder
@Entity
@Table(name = "answers")
@Getter
@Setter
@NoArgsConstructor
@AllArgsConstructor
public class Answer {

    @Id
    @GeneratedValue(strategy = GenerationType.SEQUENCE)
    private Long id;

    private String answer;

    private boolean isRight;

    @ManyToOne(fetch = FetchType.LAZY)
    @JoinColumn(name = "question_id")
    private Question question;
}

}

And I have QuestionRequestDTO with List<AnswerRequestDto>:

package com.example.demo.models.dto.request;

import lombok.*;

import java.util.List;

@Getterpackage com.example.demo.models.dto.request;

        import lombok.*;

        import java.util.List;

@Getter
@Setter
@Builder
@AllArgsConstructor
@NoArgsConstructor
public class QuestionRequestDto {
    private
@Setter
@Builder
@AllArgsConstructor
@NoArgsConstructor
public class QuestionRequestDto {
    private Integer position;
    private String question;
    private List<AnswerRequestDto> answers;
  
}

I have no idea how to connect these classes with mapstruct, servise, Restcontroller, Repository.
I try do it so:

package com.example.demo.converter.config;

import org.mapstruct.MapperConfig;
import org.mapstruct.NullValueCheckStrategy;
import org.mapstruct.NullValuePropertyMappingStrategy;

@MapperConfig(componentModel = "spring", nullValuePropertyMappingStrategy = NullValuePropertyMappingStrategy.IGNORE, nullValueCheckStrategy = NullValueCheckStrategy.ALWAYS)
public interface ConfigMapper {
}

package com.example.demo.converter;

import java.util.List;

public interface DtoMapper<D, E> {
    D toDto(E e);

    List<D> toDto(List<? extends E> eList);
}

package com.example.demo.converter.question;

import com.example.demo.converter.DtoMapper;
import com.example.demo.converter.config.ConfigMapper;
import com.example.demo.models.dto.request.AnswerRequestDto;
import com.example.demo.models.entitys.Answer;
import org.mapstruct.Mapper;

import java.util.ArrayList;
import java.util.List;
import java.util.Set;
import java.util.stream.Collectors;

@Mapper(config = ConfigMapper.class)
public interface AnswerMapper extends DtoMapper<AnswerRequestDto, Answer>{
    default List<AnswerRequestDto> toDto(Set<Answer> answers) {
        return toDto(new ArrayList<>(answers));
    }

    default Set<Answer> map(List<Long> answersIds) {
        return answersIds.stream()
                .map(id -> Answer.builder().id(id).build())
                .collect(Collectors.toSet());
    }
}

package com.example.demo.converter.question;

import com.example.demo.converter.DtoMapper;
import com.example.demo.converter.config.ConfigMapper;
import com.example.demo.models.dto.request.AnswerRequestDto;
import com.example.demo.models.dto.request.QuestionRequestDto;
import com.example.demo.models.entitys.Question;
import org.mapstruct.Mapper;

import java.util.List;

@Mapper(config = ConfigMapper.class, uses = {AnswerMapper.class})
public interface QuestionMapper extends DtoMapper<QuestionRequestDto, Question> {

    QuestionRequestDto toDto(Question question);

    default QuestionRequestDto toDto(Question question,
                                     List<AnswerRequestDto> answers) {
        QuestionRequestDto questionRequestDto = toDto(question);
        questionRequestDto.setAnswers(answers);
        return questionRequestDto;
    }
}

I have no idea how to receive DTO in service and save in Repository, call in RestController...

[Stephan van Hulst]

I'm not familiar with MapStruct, but as far as I can tell, you would just inject the mapper into your controller and then call it in one of your controller actions. Something like this:

@RestController
@RequestMapping(
  path     = "/questions",
  consumes = MediaType.APPLICATION_JSON_VALUE,
  produces = MediaType.APPLICATION_JSON_VALUE
)
public class QuestionController {

  private final QuestionMapper questionMapper;

  private final QuestionService questionService;

  @Autowired
  public QuestionController(
    QuestionMapper  questionMapper,
    QuestionService questionService
  ) {
    this.questionMapper  = questionMapper;
    this.questionService = questionService;
  }

  @GetMapping(path = "{id}")
  public QuestionRequestDto getQuestion(@PathVariable long id) {
    var entity = questionService.findQuestionById(id).orElseThrow(NotFoundException::new);
    var dto    = questionMapper.toDto(entity);

    return dto;
  }
}

I think you have to set the componentModel of your mappers to "spring" for this to work.

A word of warning. Automatic source code generation libraries are generally more trouble than they're worth. I can't speak for MapStruct, but Lombok is a huge pain.

[Himai Minh]

Here are  references to MapStruct:
https://www.baeldung.com/mapstruct

https://reflectoring.io/java-mapping-with-mapstruct/

[Himai Minh]

This educational example on Github may be helpful for you to apply @Mapper in Mapstruct:
https://github.com/springframeworkguru/spring-6-rest-mvc/blob/54-jpa-update-existing-beer/src/main/java/guru/springframework/spring6restmvc/mappers/CustomerMapper.java
https://github.com/springframeworkguru/spring-6-rest-mvc/blob/54-jpa-update-existing-beer/pom.xml
https://github.com/springframeworkguru/spring-6-rest-mvc/blob/58-assn-jpa-customer-operations/src/main/java/guru/springframework/spring6restmvc/services/CustomerServiceJPA.java