Spring中@OneToMany关联异常：无法为同一所有者添加多只宠物

问题概述 #

配置所有者（Owners）与宠物（Pets）的一对多关联时，出现无法为同一所有者添加多只宠物的异常：添加第一只宠物正常，但添加第二只时，宠物会被错误关联到其他所有者，原所有者的宠物列表无变化。

相关实体类代码 #

Owners 实体类 #

@Entity
@Table(name="owners_table")
public class Owners {
    @Id
    @GeneratedValue(strategy=GenerationType.IDENTITY)
    private Integer id;
    
    @Column(nullable=false)
    private String name;
    
    @Column(nullable=false)
    private String phoneNumber;
    
    @Column(nullable=true)
    private String email;
    
    @Column(nullable=false)
    private String address;
     
    @OneToMany(fetch=FetchType.LAZY,mappedBy="id")
    @JsonManagedReference(value="pet-owners")
    @JsonIgnore
    private List<Pets> pets;

    
    public Owners() {
        
    }
    @JsonCreator
    public Owners(Integer id, String name, String phoneNumber, String email, String address) {
        this.id = id;
        this.name = name;
        this.phoneNumber = phoneNumber;
        this.email = email;
        this.address = address;
    }
    
    // 省略getter和setter方法
}

Pets 实体类 #

@Entity
@Table(name="pets_table")
public class Pets {
    private String name;
    private String breed;
    private Date birthDate;
    
    @ManyToOne(fetch = FetchType.LAZY, cascade = CascadeType.ALL)
    @JsonBackReference(value="pet-owners")
    @JoinColumn(name = "owner_id")
    private Owners owner;

    @Id
    @GeneratedValue(strategy=GenerationType.IDENTITY)
    private Integer id;
    
    
    @ManyToOne(fetch = FetchType.LAZY, cascade = CascadeType.ALL)
    @JoinColumn(name="walk_id")
    @JsonBackReference(value="pet-walks")
    private DogWalking walk;
    

    public Pets() {
    }
    
    @JsonCreator
    public Pets(String name, String breed, Date birthDate,  Owners owner , Integer id) {
        this.name = name;
        this.breed = breed;
        this.birthDate = birthDate;
        this.id = id;
    }
    
    // 省略getter和setter方法
}

问题现象 #

• 查询id为6的所有者，初始宠物列表为空：
  请求：localhost:8080/owners/6
  返回结果：

  {
          "id": 6,
          "name": "Lucas Calado",
          "phoneNumber": "(83) 98326-9273",
          "email": "lucasthecalado@gmail.com",
          "address": "Rua Bancário João Luiz , 92",
          "pets": []
  }
  

• 为该所有者添加第一只宠物，操作成功：
  请求：localhost:8080/pets/insert
  请求体：

  {
          "name": "Fenrir",
          "breed": "Husky siberiano",
          "birthDate": "2017-03-08T03:00:00.000+00:00",
          "owner":{
              "id":6
          },
          "walks": null
  }
  

  再次查询id为6的所有者，宠物列表包含该宠物：

  {
          "id": 6,
          "name": "Lucas Calado",
          "phoneNumber": "(83) 98326-9273",
          "email": "lucasthecalado@gmail.com",
          "address": "Rua Bancário João Luiz , 92",
          "pets": [
              {
                  "name": "Fenrir",
                  "breed": "Husky siberiano",
                  "birthDate": "2017-03-08T03:00:00.000+00:00",
                  "id": 6,
                  "walks": null
              }
          ]
      }
  

• 尝试为同一所有者添加第二只宠物时，该宠物被错误关联到id为7的所有者，id为6的所有者宠物列表无变化：
  请求：localhost:8080/pets/insert
  请求体：

  {
      "name": "Roabson",
      "breed": "Pug",
      "birthDate": "2018-12-02T03:00:00.000+00:00",
      "owner":{
          "id":6
      }
  }
  

解决方案 #

1. 修正@OneToMany的mappedBy属性 #

Owners类中@OneToMany注解的mappedBy参数值错误，应指向Pets类中关联Owners的属性名owner，而非id。修改后代码：

@OneToMany(fetch=FetchType.LAZY,mappedBy="owner")
@JsonManagedReference(value="pet-owners")
@JsonIgnore
private List<Pets> pets;

mappedBy用于指定双向关联中被动方（多的一方）的关联属性，这里Pets类用private Owners owner;关联所有者，必须设为owner才能正确建立关联。

2. 优化宠物添加的业务逻辑 #

添加宠物时，需从数据库获取持久化状态的Owners对象，而非仅用id构造临时对象。示例代码：

public Pets insertPet(Pets pet) {
    // 查询数据库获取持久化的所有者对象
    Owners owner = ownerRepository.findById(pet.getOwner().getId())
            .orElseThrow(() -> new RuntimeException("所有者不存在"));
    pet.setOwner(owner);
    // 维护双向关联一致性：将宠物添加到所有者的宠物列表
    owner.getPets().add(pet);
    ownerRepository.save(owner);
    return petRepository.save(pet);
}

避免临时对象导致的关联异常，同时保证双向关联数据一致。

3. 修正Pets构造函数 #

Pets的@JsonCreator构造函数未设置owner属性，导致反序列化时无法正确关联所有者。修改后：

@JsonCreator
public Pets(String name, String breed, Date birthDate, Owners owner, Integer id) {
    this.name = name;
    this.breed = breed;
    this.birthDate = birthDate;
    this.owner = owner; // 补充设置owner属性
    this.id = id;
}

内容的提问来源于stack exchange，提问作者vitoriac