时间戳

首页 > 解决方案 > JPA 在插入/更新时返回完整的外键实体

java - JPA 在插入/更新时返回完整的外键实体

问题描述

我的目标是能够插入下面的对象，用户传入相关数据和外键的 id，并向用户返回一个包含完整外键对象的完整对象，而不仅仅是外键密钥标识。

@Data
@Entity
@EqualsAndHashCode(callSuper = false)
@Table(name = MY_OBJECT_TABLE)
public class MyObject {

    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    @Column(name = "MY_OBJECT_ID", unique = true, nullable = false)
    private Integer myObjectId;

    @ManyToOne(targetEntity = ForeignObject.class, fetch = FetchType.EAGER)
    @JoinColumn(name = "FOREIGN_OBJECT_ID", referencedColumnName = "FOREIGN_OBJECT_ID", nullable = false, insertable = false, updatable = false)
    private ForeignObject foreignObject;

    @Column(name = "FOREIGN_OBJECT_ID")
    private Integer foreignObjectId;

    @Column(name = "RANDOM_FIELD", nullable = false)
    @NotNull
    private Boolean randomField;
}

我正在尝试使用上述方法并插入但它只返回插入时的 foreignObjectId 而不是整个外来对象。

我尝试了以下方法以使其正常工作，但没有运气。

    @Transactional
    public MyObject create(MyObject myObject) {
        MyObject createdMyObject = this.myObjectRepository.save(myObject);
        return createdMyObject;
    }

也试过

    @Transactional
    public MyObject create(MyObject myObject) {
        MyObject createdMyObject = this.myObjectRepository.save(myObject);
        return this.myObjectRepository.findById(createdMyObject.getMyObjectId());
    }

我不确定我的域对象中是否有需要更改的内容，或者是否需要以某种方式更改我的创建方法。

当前输出为：

{
  "myObjectId": 1,
  "foreignObject": null,
  "foreignObjectId": 3,
  "randomField": true
}

预期输出为：

{
  "myObjectId": 1,
  "foreignObject": {
    "foreignObjectId": 3,
  },
  "foreignObjectId": 3, // I don't care if this field stays here or not
  "randomField": true
}

标签： javamysqlhibernatejpa

解决方案

问题在于您正在破坏域模型以尝试使其适合某些前端问题：

@ManyToOne(targetEntity = ForeignObject.class, fetch = FetchType.EAGER)
@JoinColumn(name = "FOREIGN_OBJECT_ID", referencedColumnName = "FOREIGN_OBJECT_ID", 
                       nullable = false, insertable = false, updatable = false)
private ForeignObject foreignObject;

@Column(name = "FOREIGN_OBJECT_ID")
private Integer foreignObjectId;

您永远不会设置关系，而只是设置整数字段。

这将不起作用，因为调用EntityManager#persist（通过 myObjectRepository.save）只是获取现有对象并使其持久化，即不会触发设置对 ForeignObject 的引用。

@Transactional
public MyObject create(MyObject myObject) {

    //createdMyObject and  myObject are same instance  

    MyObject createdMyObject = this.myObjectRepository.save(myObject);
    return createdMyObject;
}

这将不起作用，因为将简单地从 Hibernate 的一级缓存中检索相同的实例（即您创建的没有关系集的实例）：

   @Transactional
    public MyObject create(MyObject myObject) {
        //createdMyObject, myObject and (due to 1st level cache) 
        //object returned from query are same 

        MyObject createdMyObject = this.myObjectRepository.save(myObject);
        return this.myObjectRepository.findById(createdMyObject.getMyObjectId());
    }

您可以通过执行以下操作可能使方法 2 起作用，但是正确的解决方案是删除 Integer 字段并正确设置关系。Spring MVC 控制器应该在 POST/PUT 请求中自动设置来自 ID 的引用{... "foreignObject" : 3 ...}

   @PersistenceContect
   EntityManager em;

   @Transactional
    public MyObject create(MyObject myObject) {
        this.myObjectRepository.saveAndFlush(myObject);
        em.clear(); //force reload from database
        return this.myObjectRepository.findById(createdMyObject.getMyObjectId());
    }

推荐阅读