英文:
Spring Data JPA: How to join two entities using annotations
问题
我有两个实体（Student和Project），想要通过外键"student_id"将它们连接起来。
@Entity
@Data
public class Project {
@Id
@GeneratedValue(strategy = GenerationType.IDENTITY)
private Long id;
private String title;
private Long student_id;
}
@Entity
@Data
public class Student {
@Id
@GeneratedValue(strategy = GenerationType.IDENTITY)
private Long id;
private String name;
@OneToMany
private List<Project> projects;
}
简单来说，当我向Student存储库发送GET请求时，我想要获得带有项目列表的学生。
例如;
// > 用于POST到Project的JSON
{
"title":"java",
"student_id":1
}
// > 用于POST到Student的JSON
{
"name":"Bill Gates"
}
当我向Student发送GET请求时，我希望看到的内容如下;
[
{
"id":1,
"name":"java",
"projects":[
{
"id":1,
"title":"java"
}
]
}
]
是否可以只使用JPA注解来实现？提前感谢。
英文:
I have two entities(Student and Project) and want to join them by foreign key "student_id"
@Entity
@Data
public class Project {
@Id
@GeneratedValue(strategy = GenerationType.IDENTITY)
private Long id;
private String title;
private Long student_id;
}
@Entity
@Data
public class Student {
@Id
@GeneratedValue(strategy = GenerationType.IDENTITY)
private Long id;
private String name;
@OneToMany
private List<Project> projects;
}
Simply, I want to get students with project list when I send GET request to Student repository.
For example;
// > json for POST to Project
{
"title":"java",
"student_id":1
}
// > json for POST to Student
{
"name":"Bill Gates"
}
What I expect to see when I send GET request to Student is simply like this below;
[
{
"id":1,
"name":"java",
"projects":[
{
"id":1,
"title":"java"
}
]
}
]
Is it applicable using only JPA annotations? Thanks in advance.
答案1
得分: 0
是的，这是适用的。
首先，在你的Project类中，你需要将student_id更改为student类，像这样：
@ManyToOne(fetch=FetchType.LAZY)
@JoinColumn(name = "student_id",nullable = false)
private Student student;
其次，你需要在你的oneToMany注解中添加'map'参数：
@OneToMany(mappedBy = "student")
private List<Project> projects;
就是这样。
另外注意：如果多名学生可以分配给同一个项目，你还可以考虑多对多的关系。
英文:
Yes, it's applicable.
First, you need to change the student_id to student class like this in your Project class
@ManyToOne(fetch=FetchType.LAZY)
@JoinColumn(name = "student_id",nullable = false)
private Student student;
Second, you need to add 'map' parameter to you oneToMany annotation
@OneToMany(mappedBy = "student")
private List<Project> projects;
and that's it.
Side note: you can also consider manytomany relationship if more than one student can be assigned to the same project
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