JpaRepository 返回列表中第一项的子项，然后仅返回其余项的 id

Question

我有以下 Post class:

@Entity
@Table(name = "posts")
@Getter
@Setter
@JsonIdentityInfo(      generator = ObjectIdGenerators.PropertyGenerator.class, 
                        property  = "id", 
                        scope     = Long.class)
public class Post {
    
    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    private Long id;
    
    private String title;
    
    private String subtitle;
    
    private String content;
    
    private String img_url;
    
    @CreationTimestamp
    private Timestamp created_on;
    
    @UpdateTimestamp
    private Timestamp last_updated_on;
    
    @ManyToOne(fetch = FetchType.EAGER)
    @JoinColumn(name = "owner_id", nullable=false)
    @JsonIgnoreProperties({"hibernateLazyInitializer", "handler"})
    private User creator;
    
}

以及扩展 JpaRepository 的以下存储库

@Repository
public interface PostRepository extends JpaRepository<Post, Long> {

    Optional<Post> findById(Long id);
    
    List<Post> findAll();
    
}

在以下控制器中返回 findAll() 的结果时，只有第一个创建者项目被完整发送，其余仅包含 id：

@GetMapping("/news")
    public List<Post> getNews() {
        return postRepository.findAll();
    }

这是 JSON 我得到的结果：

[
{"id":15,"title":"Title example #1","subtitle":"Subtitle example #1","content":"Lorem #1 ipsum dolor sit amet","img_url":null,"created_on":"2021-12-01T00:00:00.000+00:00","last_updated_on":"2021-12-01T00:00:00.000+00:00","creator":{"id":1,"username":"user-example","email":"blablabla@gmail.com","roles":[{"id":1,"name":"ROLE_USER"}]}}

,{"id":25,"title":"Title example #2","subtitle":"Subtitle example #2","content":"Lorem #2 ipsum dolor sit amet","img_url":null,"created_on":"2021-12-01T00:00:00.000+00:00","last_updated_on":"2021-12-01T00:00:00.000+00:00","creator":1}
]

为什么会这样？有没有一种方法可以为 JSON 数组中的每个元素获取整个子对象？

谢谢

编辑：添加了 User class

@Entity
@Table( name = "users", 
        uniqueConstraints = { 
            @UniqueConstraint(columnNames = "username"),
            @UniqueConstraint(columnNames = "email") 
        })
@DiscriminatorValue(value="USER")
public class User extends OwnerEntity {

    @NotBlank
    @NotNull
    @Size(max = 20)
    private String username;

    @NotBlank
    @NotNull
    @Size(max = 50)
    @Email
    private String email;

    @NotBlank
    @Size(max = 120)
    @JsonIgnore
    private String password;
    
    @CreationTimestamp
    private Timestamp created_on;
    
    @UpdateTimestamp
    private Timestamp last_updated_on;

    @ManyToMany(fetch = FetchType.LAZY)
    @JoinTable( name = "user_roles", 
                joinColumns = @JoinColumn(name = "user_id"), 
                inverseJoinColumns = @JoinColumn(name = "role_id"))
    private Set<Role> roles = new HashSet<>();

    @ManyToMany(fetch = FetchType.LAZY)
    private Set<Institution> institutions;
    
    @OneToMany(mappedBy="creator", fetch = FetchType.LAZY, cascade = CascadeType.ALL)
    protected Set<Post> posts;
    
    @ManyToMany(fetch = FetchType.LAZY)
    private Set<Institution> following;
}

编辑 2：添加了 OwnerEntity class

@Entity
@Table(name = "entities")
@Inheritance(strategy = InheritanceType.JOINED)
@DiscriminatorColumn
@Getter
@Setter
@JsonIdentityInfo(      generator = ObjectIdGenerators.PropertyGenerator.class, 
                        property  = "id", 
                        scope     = Long.class)
public class OwnerEntity {
    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    protected Long id;
    
}

Answer 1

你的 OwnerEntity 还有 @JsonIdentityInfo。在它的 reference documentation 中我们可以读到以下内容：

Annotation used for indicating that values of annotated type or property should be serializing so that instances either contain additional object identifier (in addition actual object properties), or as a reference that consists of an object id that refers to a full serialization. In practice this is done by serializing the first instance as full object and object identity, and other references to the object as reference values.

这完美地解释了为什么您会得到这样的 JSON。如果您不想要这个，只需删除 @JsonIdentityInfo 但它可能会在序列化双向关系时修复无限递归（您可以在以下在线资源 https://www.baeldung.com/jackson-bidirectional-relationships-and-infinite-recursion 中阅读更多相关信息）。

JpaRepository 返回列表中第一项的子项，然后仅返回其余项的 id

JpaRepository returning child for the first item in the list and then only the id for the rest

spring

hibernate

spring-data-jpa

spring-boot