java - 如何使用 Spring Data Jpa OneToMany 嵌套模型对 Spring Boot Restful API 进行 CURD 操作？

Question

我试图制作一个 CRUD 应用程序，它有两个类型为“肌肉”和“锻炼”的模型对象。基本上一个肌肉对象可以有一个锻炼对象列表。我想为两个模型对象实现 CRUD 操作。对于 Muscle 对象，它非常简单，但对于放置/更新操作的练习对象，我收到以下错误“JSON 解析错误:未解析的前向引用:；嵌套异常是 com.fasterxml.jackson.databind.deser.UnresolvedForwardReference ”。此外，如果我尝试删除一项锻炼，不知何故，所有肌肉和锻炼的数据都会被删除。

这是我的肌肉等级

    package com.fazla.exercise.model;

    import java.util.ArrayList;
    import java.util.List;

    import javax.persistence.CascadeType;
    import javax.persistence.Column;
    import javax.persistence.Entity;
    import javax.persistence.FetchType;
    import javax.persistence.GeneratedValue;
    import javax.persistence.GenerationType;
    import javax.persistence.Id;
    import javax.persistence.JoinColumn;
    import javax.persistence.OneToMany;

    import com.fasterxml.jackson.annotation.JsonIdentityInfo;
    import com.fasterxml.jackson.annotation.ObjectIdGenerators;


    @Entity
    @JsonIdentityInfo(generator=ObjectIdGenerators.IntSequenceGenerator.class, property="id")
    public class Muscle {

        @Id
    //  @Column(unique = true, nullable = false)
        @GeneratedValue(strategy = GenerationType.AUTO)
        private Long id;

        @Column
        private String name;

        @OneToMany(mappedBy="muscle", cascade= CascadeType.ALL, fetch = FetchType.EAGER)
    //  @JoinColumn(name="muscle_id")
    //  @Column(nullable = true)
        private List<Exercise> exercises = new ArrayList<>();

        public Muscle() {

        }

        public Muscle(String name, List<Exercise> exercises) {
            super();
            this.name = name;
            this.exercises = exercises;
        }

        public Long getId() {
            return id;
        }

        public void setId(Long id) {
            this.id = id;
        }

        public String getName() {
            return name;
        }

        public void setName(String name) {
            this.name = name;
        }

        public List<Exercise> getExercises() {
            return exercises;
        }

        public void setExercises(List<Exercise> exercises) {
            this.exercises = exercises;
        }

    //  @Override
    //  public String toString() {
    //      return "Muscle [id=" + id + ", name=" + name + ", exercises=" + exercises + "]";
    //  }



}

这是我的练习对象

    package com.fazla.exercise.model;

import javax.persistence.CascadeType;
import javax.persistence.Column;
//import javax.persistence.Column;
import javax.persistence.Entity;
import javax.persistence.GeneratedValue;
import javax.persistence.GenerationType;
import javax.persistence.Id;
import javax.persistence.JoinColumn;
import javax.persistence.JoinTable;
import javax.persistence.ManyToOne;

import com.fasterxml.jackson.annotation.JsonIdentityInfo;
import com.fasterxml.jackson.annotation.ObjectIdGenerators;

@Entity
//@JsonIdentityInfo(generator=ObjectIdGenerators.IntSequenceGenerator.class, property="id")
public class Exercise {
    @Id
    @Column(unique = true, nullable = false)
    @GeneratedValue(strategy = GenerationType.AUTO)
    private long id;

    @Column
    private String name;

    @Column
    private String description;


    //As there will be many exercise under one muscle that is why manytoone
    //object references an unsaved transient instance - save the transient instance before flushing 
    //that is why need to add the cascading dependencies
    @ManyToOne(cascade = CascadeType.ALL)
    @JoinColumn(name="muscle_id")
//  @JsonIgnore
//  @JoinTable(name="muscle")
    private Muscle muscle;

    public Exercise() {

    }

    public Exercise(String name, String description, Muscle muscle) {
        super();
        this.name = name;
        this.description = description;
        this.muscle = muscle;
    }

    public long getId() {
        return id;
    }

    public void setId(long id) {
        this.id = id;
    }

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public String getDescription() {
        return description;
    }

    public void setDescription(String description) {
        this.description = description;
    }

    public Muscle getMuscle() {
        return muscle;
    }

    public void setMuscle(Muscle muscle) {
        this.muscle = muscle;
    }

//  @Override
//  public String toString() {
//      return "Exercise [id=" + id + ", name=" + name + ", description=" + description + ", muscle=" + muscle + "]";
//  }



}

这是肌肉 Controller

package com.fazla.exercise.controller;

import java.util.List;

import org.springframework.web.bind.annotation.DeleteMapping;
import org.springframework.web.bind.annotation.GetMapping;
import org.springframework.web.bind.annotation.PathVariable;
import org.springframework.web.bind.annotation.PostMapping;
import org.springframework.web.bind.annotation.PutMapping;
import org.springframework.web.bind.annotation.RequestBody;
import org.springframework.web.bind.annotation.RestController;

import com.fazla.exercise.model.Muscle;
import com.fazla.exercise.repository.MuscleRepository;

@RestController
public class MuscleController {

    private MuscleRepository muscleRepository;

    public MuscleController(MuscleRepository muscleRepository) {

        this.muscleRepository = muscleRepository;
    }

    @GetMapping("/muscle")
    List<Muscle> all(){
        return muscleRepository.findAll();
    }

    @PostMapping("/muscle")
    Muscle newMuscle(@RequestBody Muscle muscle) {
        return muscleRepository.save(muscle);
    }

    @GetMapping("/muscle/{id}")
    Muscle one(@PathVariable Long id) {
        return muscleRepository.findById(id)
                    .orElse(null);
    }

    @PutMapping("/muscle/{id}")
    Muscle updateMuscle(@RequestBody Muscle newMuscle, @PathVariable Long id) {
        return muscleRepository.findById(id)
                .map(muscle ->{
                    muscle.setName(newMuscle.getName());
                    muscle.setExercises(newMuscle.getExercises());
                    return muscleRepository.save(muscle);
                })
                .orElse(null);
    }

    @DeleteMapping("/muscle/{id}")
    void deleteMuscle(@PathVariable Long id){
        muscleRepository.deleteById(id);
    }

}

这是ExerciseController类

package com.fazla.exercise.controller;

import java.util.List;

import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.web.bind.annotation.DeleteMapping;
import org.springframework.web.bind.annotation.GetMapping;
import org.springframework.web.bind.annotation.PathVariable;
import org.springframework.web.bind.annotation.PostMapping;
import org.springframework.web.bind.annotation.PutMapping;
import org.springframework.web.bind.annotation.RequestBody;
import org.springframework.web.bind.annotation.RequestParam;
import org.springframework.web.bind.annotation.RestController;

import com.fazla.exercise.model.Exercise;
import com.fazla.exercise.model.Muscle;
import com.fazla.exercise.repository.ExerciseRepository;
import com.fazla.exercise.repository.MuscleRepository;

@RestController
public class ExerciseController {

    private ExerciseRepository repository;

    private MuscleRepository muscleRepository;

    @Autowired
    public ExerciseController(ExerciseRepository repository, MuscleRepository muscleRepository) {
        super();
        this.repository = repository;
        this.muscleRepository=muscleRepository;
    }

    @GetMapping("/exercise")
    public List<Exercise> getAll() {
        return repository.findAll();
    }

    @PostMapping("/exercise")
    public Exercise newExercise(@RequestBody Exercise newExercise, @RequestParam 
            Long muscleId) {

        Muscle muscle = muscleRepository.findById(muscleId).orElse(null);
        newExercise.setMuscle(muscle);

        return repository.save(newExercise);
    }

    @DeleteMapping("/exercise/{id}")
    public void deleteExercise(@PathVariable Long id) {
        repository.deleteById(id);
    }

    @GetMapping("/exercise/{id}")
    public Exercise one(@PathVariable Long id) {
        return repository.findById(id).orElse(null);
    }

    @PutMapping("/exercise/{id}")
    public Exercise updateExercise(@RequestBody Exercise newExercise, @PathVariable Long id) {
            return repository.findById(id)
                    .map(//map a function which maps 
                        e ->{
                        e.setName(newExercise.getName());
                        e.setDescription(newExercise.getDescription());
                        e.setMuscle(newExercise.getMuscle());
                        return repository.save(e);
                    })
                    .orElse(null);
    }
}

这是我的ExerciseRepository

包 com.fazla.exercise.repository;

import org.springframework.data.jpa.repository.JpaRepository;

import com.fazla.exercise.model.Exercise;

public interface ExerciseRepository extends JpaRepository<Exercise, Long> {

}

这是 MuscleRepository

包 com.fazla.exercise.repository;

import org.springframework.data.jpa.repository.JpaRepository;

import com.fazla.exercise.model.Muscle;

public interface MuscleRepository extends JpaRepository<Muscle, Long>{

}

如果我尝试放置请求或更新练习对象，就会出现此错误

"timestamp": "2018-10-10T06:30:46.924+0000",
"status": 400,
"error": "Bad Request",
"message": "JSON parse error: Unresolved forward references for: ; nested exception is com.fasterxml.jackson.databind.deser.UnresolvedForwardReference: Unresolved forward references for: \n at [Source: (PushbackInputStream); line: 23, column: 1]Object id [1] (for `com.fazla.exercise.model.Muscle`) at [Source: (PushbackInputStream); line: 13, column: 28], Object id [1] (for `com.fazla.exercise.model.Muscle`) at [Source: (PushbackInputStream); line: 19, column: 28].",
"path": "/api/exercise/14"

Answer 1

解决方案是在 Parent/Muscle 模型上添加 orphanRemoval= true

    @OneToMany(mappedBy="muscle", cascade= CascadeType.ALL, orphanRemoval= true)
    private List<Exercise> exercises = new ArrayList<>();

删除子/练习模型中的cascade= CascadeType.ALL

@ManyToOne
private Muscle muscle;

对于 updateExercise，通过查找锻炼所属的肌肉和muscleRepository.findById(muscleId) 并将其设置在新的锻炼对象中来更改请求。

    @PutMapping("/exercise/{id}")
public Exercise updateExercise(@RequestBody Exercise newExercise, @PathVariable Long id, @RequestParam Long muscleId) {
    Muscle muscle = muscleRepository.findById(muscleId).orElse(null);
        return repository.findById(id)
                .map(//map a function which maps 
                    e ->{
                    e.setName(newExercise.getName());
                    e.setDescription(newExercise.getDescription());
                    e.setMuscle(muscle);
                    return repository.save(e);
                })
                .orElse(null);
}