使用 Hibernate 插入嵌套实体

Question

我想弄清楚如何正确地将多个实体插入到数据库中，这些实体具有另一个实体作为字段，并且在休眠中这似乎是一项非常重要的任务。当我把所有东西都整理得井井有条时，它工作正常，但是一旦它们交叉链接，它就无法按预期工作。我假设我缺少一些使其工作所需的注释，但经过几个小时的谷歌搜索后，我找不到任何 suitable 来及时解决它。

我目前的实体是这样设置的我有一个学生和

@Entity
@Data
@NoArgsConstructor
@AllArgsConstructor
public class Student {

    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    private int id;
    private String name;
}

我有一个教室，里面有一个学生实体，通过它的 id

@Entity
@Data
@NoArgsConstructor
@AllArgsConstructor
public class ClassRoom {
    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    private Long id;

    @ManyToOne(fetch = FetchType.LAZY)
    @JoinColumn(name = "student_id", foreignKey = @ForeignKey(name = "fk_student"))
    private Student student;

    private String dateCreated;
}

我有一个 json，当我尝试将它存储到数据库中时，它工作得很好：

{
   "dateCreated":"17",
   "body":[
      {
         "id":1,
         "student":{
            "id":1,
            "name":"petya",
            "hibernateLazyInitializer":{

            }
         },
         "dateCreated":"17"
      },
      {
         "id":2,
         "student":{
            "id":2,
            "name":"petrya",
            "hibernateLazyInitializer":{

            }
         },
         "dateCreated":"17"
      },
      {
         "id":3,
         "student":{
            "id":3,
            "name":"slon",
            "hibernateLazyInitializer":{

            }
         },
         "dateCreated":"17"
      }
   ]
}

Hibernate: select student0_.id as id1_1_0_, student0_.name as name2_1_0_ from json_schema.student student0_ where student0_.id=?
Hibernate: select student0_.id as id1_1_0_, student0_.name as name2_1_0_ from json_schema.student student0_ where student0_.id=?
Hibernate: select student0_.id as id1_1_0_, student0_.name as name2_1_0_ from json_schema.student student0_ where student0_.id=?
Hibernate: select classroom0_.id as id1_0_0_, classroom0_.date_created as date_cre2_0_0_, classroom0_.student_id as student_3_0_0_ from json_schema.class_room classroom0_ where classroom0_.id=?
Hibernate: select classroom0_.id as id1_0_0_, classroom0_.date_created as date_cre2_0_0_, classroom0_.student_id as student_3_0_0_ from json_schema.class_room classroom0_ where classroom0_.id=?
Hibernate: select classroom0_.id as id1_0_0_, classroom0_.date_created as date_cre2_0_0_, classroom0_.student_id as student_3_0_0_ from json_schema.class_room classroom0_ where classroom0_.id=?
Hibernate: update json_schema.class_room set date_created=?, student_id=? where id=?
Hibernate: update json_schema.class_room set date_created=?, student_id=? where id=?
Hibernate: update json_schema.class_room set date_created=?, student_id=? where id=?

但是一旦我尝试保存链接到第三个学生的第二个教室条目，例如像这样：

{
   "dateCreated":"10",
   "body":[
      {
         "id":1,
         "student":{
            "id":1,
            "name":"petya",
            "hibernateLazyInitializer":{

            }
         },
         "dateCreated":"10"
      },
      {
         "id":2,
         "student":{
            "id":3,
            "name":"slon",
            "hibernateLazyInitializer":{

            }
         },
         "dateCreated":"10"
      },
      {
         "id":3,
         "student":{
            "id":2,
            "name":"petrya",
            "hibernateLazyInitializer":{

            }
         },
         "dateCreated":"10"
      }
   ]
}

Hibernate: select student0_.id as id1_1_0_, student0_.name as name2_1_0_ from json_schema.student student0_ where student0_.id=?
Hibernate: insert into json_schema.student (name) values (?)
Hibernate: select student0_.id as id1_1_0_, student0_.name as name2_1_0_ from json_schema.student student0_ where student0_.id=?
Hibernate: insert into json_schema.student (name) values (?)
Hibernate: update json_schema.student set name=? where id=?
Hibernate: select classroom0_.id as id1_0_0_, classroom0_.date_created as date_cre2_0_0_, classroom0_.student_id as student_3_0_0_ from json_schema.class_room classroom0_ where classroom0_.id=?
Hibernate: insert into json_schema.class_room (date_created, student_id) values (?, ?)
Hibernate: select classroom0_.id as id1_0_0_, classroom0_.date_created as date_cre2_0_0_, classroom0_.student_id as student_3_0_0_ from json_schema.class_room classroom0_ where classroom0_.id=?
Hibernate: insert into json_schema.class_room (date_created, student_id) values (?, ?)

它中断：

错误：在 table "class_room" 上插入或更新违反了外键约束 "fk_student" 详细信息：密钥 (student_id)=(3) 不存在于 table "student".

中

这可能是我正在实现的逻辑，我正在尝试以这种方式存储它们：

final ClassRoom[] classRooms = objectMapper.readValue(parser, ClassRoom[].class);
        final List<ClassRoom> classRoomList = Arrays.asList(classRooms);
        final List<Student> studentsList = new ArrayList<>();
        for (final ClassRoom classRoom : classRoomList) {
            studentsList.add(classRoom.getStudent());

        }
        studentRepo.saveAll(studentsList);
        classRoomRepo.saveAll(classRoomList);

但是我不知道如何先单独存储学生，然后再存储classRooms。感谢任何帮助。希望随着时间的推移解决它，如果是这样，我会 post 自己回答。

Answer 1

您的 id 方法是 @GeneratedValue(strategy = GenerationType.IDENTITY)，而您的学生和班级列表都预先填充了 id。如果你想让那些 id 进入 json，删除 @GeneratedValue(strategy = GenerationType.IDENTITY) 注释。

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