我正试图弄清楚如何正确地将多个实体插入到数据库中，而这些实体又有另一个实体作为字段，似乎在hibernate中这是一个有点非同小可的任务。当我把所有的东西都排列整齐时，它工作得很好，但是当它们被交叉链接时，它就不能如愿了。我认为我缺少了一些所需的注释来使它工作，但经过几个小时的google，我无法找到任何合适的方法来及时解决它。
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连接起来。
@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，当我试图将它存储到db中时，它的工作非常完美。
{
"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第二个教室条目，链接到第三个学生，比如这个，
{
"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 (?, ?)
它的错误是：
ERROR: insert or update on table "class_room" violates foreign key constraint "fk_student" Detail: 表 "student "中不存在键(student_id)=(3)。
可能是我实现的逻辑问题，我想这样存储。
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);
但我不知道如何先分别存储学生，然后再存储classRooms。感谢大家的帮助。希望会随着时间的推移解决，如果有，自己会发帖解答。
你对id的处理方法是 @GeneratedValue(strategy = GenerationType.IDENTITY)而你的学生列表和教室列表都已经提前填充了id。如果你想保持这些id在json中的存在，请去掉 @GeneratedValue(strategy = GenerationType.IDENTITY) 注释。