如何创建具有JPA注释的连接表？ [英] How to create join table with JPA annotations?

问题描述

我需要在我的数据库中使用JPA注释创建一个连接表，因此结果将是：

到目前为止，我只是实现了2个实体：

  @Entity 
 @Table（name =USERS，schema =ADMIN）
 public class用户实现Serializable {
 
 private static final long serialVersionUID = -1244856316278032177L; 
 @Id 
 @Column（nullable = false）
 private String userid; 
 
 @Column（nullable = false）
 private String password; 
 
 public String getUserid（）{
 return userid; 
} 
 
 public void setUserid（String userid）{
 this.userid = userid; 
} 
 
 public String getPassword（）{
 return password; 
} 
 
 public void setPassword（String password）{
 this.password = password; 
} 
 
} 
  

---

$ b b

  @Entity 
 @Table（name =GROUPS，schema =ADMIN）
 public class Group implements Serializable {
 
 private static final long serialVersionUID = -7274308564659753174L; 
 @Id 
 @Column（nullable = false）
 private String groupid; 
 
 public String getGroupid（）{
 return groupid; 
} 
 public void setGroupid（String groupid）{
 this.groupid = groupid; 
} 
} 
  

如果我创建另一个实体叫做USER_GROUP，添加一些注释，所以当我从实体（ORM）运行创建表时，将自动创建连接表？

我应该如何注释我的实体以实现与图像？

解决方案

你绝对不应该创建User_Group实体，因为它比面向对象的基础数据库表示更多。 / p>

您可以通过定义以下内容来实现连接表：

  @实体
 @Table（name =USERS，schema =ADMIN）
 public class用户实现Serializable {
 // ... 
 
 @ManyToOne 
 @JoinTable（name =USER_GROUP）
组组; 
  

---

  @实体
 @Table（name =GROUPS，schema =ADMIN）
 public class Group implements Serializable {
 // ... 
 
 @OneToMany mappedBy =group）
设置< User>用户; 
  

编辑：如果要显式设置列的名称可以使用@JoinColumn元素，如下所示：

  @ManyToOne 
 @JoinTable（name =USER_GROUP，
 joinColumns = @JoinColumn（name =userid，
 referencedColumnName =userid），
 inverseJoinColumns = @JoinColumn（name =groupid，
 referencedColumnName =groupid）） 
组群; 
  

I need to create a join table in my database ussing JPA annotations so the result will be this:

So far i just implemented 2 entities:

@Entity
@Table(name="USERS", schema="ADMIN")
public class User implements Serializable {

    private static final long serialVersionUID = -1244856316278032177L;
    @Id 
    @Column(nullable = false)
    private String userid;  

    @Column(nullable = false)
    private String password;

    public String getUserid() {
        return userid;
    }

    public void setUserid(String userid) {
        this.userid = userid;
    }

    public String getPassword() {
        return password;
    }

    public void setPassword(String password) {
        this.password = password;
    }

}

---

@Entity
@Table(name="GROUPS", schema="ADMIN")
public class Group implements Serializable {

    private static final long serialVersionUID = -7274308564659753174L;
    @Id
    @Column(nullable = false)
    private String groupid;

    public String getGroupid() {
        return groupid;
    }
    public void setGroupid(String groupid) {
        this.groupid = groupid;
    }
}

Should i create another entity called USER_GROUP or i can just add some annotations, so the join table will be created automatically when i run create tables from entities(ORM)?

How should i annotate my entities to achieve the same as in the image?

解决方案

You definitely shouldn't create User_Group entity as it's more the underlying database representation than the object oriented one.

You can achieve the join table by defining something like:

@Entity
@Table(name="USERS", schema="ADMIN")
public class User implements Serializable {
//...

@ManyToOne
@JoinTable(name="USER_GROUP")
Group group;

---

@Entity
@Table(name="GROUPS", schema="ADMIN")
public class Group implements Serializable {
//...

@OneToMany(mappedBy="group")
Set<User> users;

Edit: If you want to explicitly set the names of the columns you could use @JoinColumn elements as shown below:

@ManyToOne
@JoinTable(name="USER_GROUP",
    joinColumns = @JoinColumn(name = "userid", 
                              referencedColumnName = "userid"), 
    inverseJoinColumns = @JoinColumn(name = "groupid", 
                              referencedColumnName = "groupid"))
Group group;

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