Java Spring Data JPA 无法获取关联表数据

Question

我有以下实体类，
一个 AppUser 可以有 1 个个人资料和多个帖子，
1 个帖子只能与 1 个 AppUser 关联，
AppUser和Role会多对多关联。

ERD-

AppUser - 

@Getter
@Setter
@Entity
@Table(name = "app_user")
public class AppUser {
    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    private Long id;

    @Column(name = "username")
    private String username;

    @Column(name = "email")
    private String email;

    @JsonManagedReference
    @OneToOne(cascade = CascadeType.ALL, fetch = FetchType.EAGER)
    @JoinColumn(name = "profile_id")
    private Profile profile;

    @JsonManagedReference
    @OneToMany(mappedBy = "appUser", cascade = CascadeType.ALL, fetch = FetchType.EAGER)
    private List<Post> posts = new ArrayList<>();

    @JsonBackReference
    @ManyToMany
    @JoinTable(
            name = "user_role",
            joinColumns = @JoinColumn(name = "user_id"),
            inverseJoinColumns = @JoinColumn(name = "role_id")
    )
    private Set<Role> roles = new HashSet<>();
}


Profile -

@Getter
@Setter
@Entity
@Table(name = "profile")
public class Profile {

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

    private String bio;
}


Post -

@Getter
@Setter
@Entity
@Table(name = "post")
public class Post {

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

    private String content;

    @JsonBackReference
    @ManyToOne
    @JoinColumn(name = "app_user_id")
    private AppUser appUser;
}


Role -

@Getter
@Setter
@Entity
@Table(name = "role")
public class Role {

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

    private String name;

    @ManyToMany(mappedBy = "roles")
    private Set<AppUser> appUsers = new HashSet<>();
}

当我执行简单的 userRepository.findAll(); 时，我得到以下响应，其中未获取角色数据

// http://localhost:8080/user/all

[
  {
    "id": 1,
    "username": "john_doe",
    "email": "[email protected]",
    "profile": {
      "id": 1,
      "bio": "This is John Doe's bio."
    },
    "posts": [
      {
        "id": 1,
        "content": "Content of post 1"
      },
      {
        "id": 2,
        "content": "Content of post 2"
      }
    ]
  },
  {
    "id": 2,
    "username": "jane_smith",
    "email": "[email protected]",
    "profile": {
      "id": 2,
      "bio": "This is Jane Smith's bio."
    },
    "posts": [
      {
        "id": 3,
        "content": "Content of post 3"
      }
    ]
  }
]

Answer 1

您需要对

@JsonManagedReference

 实体中的 

roles

 字段使用 

AppUser

，对 

@JsonBackReference

 实体中的 

appUsers

 字段使用 

Role

。而且很可能您还需要在加载用户时使用 

@EntityGraph(attributePaths = "roles")

 以避免 

LazyInitializationException

，或者您可以为 

fetch = FetchType.EAGER

 字段添加 

roles

。