没有@EmbeddedId或@IdClass的超级简单组合键 [英] Super simple composite key without @EmbeddedId or @IdClass

问题描述

我不知道，因为这是可能的，但我只是按照我一直想要的方式创建组合键：无 @EmbeddedId 并且没有 @IdClass 必需!!

• Spring 4.0.0.M3


• Hibernate 4.3.0.Beta4


• JPA 2.1

User.java ：

  @Entity 
 public class User {
 @Id 
 .. 
 
 @OneToMany（的mappedBy = 用户，级联= CascadeType.ALL，orphanRemoval =真）
私人列表与LT; GroupUser> groupUsers; 
 
  

Group.java ：

  @Entity 
 public class Group {
 @Id 
 ... 
 
 @OneToMany（mappedBy =user，cascade = CascadeType.ALL，orphanRemoval = true）
 private List< GroupUser> groupUsers; 
 
  

GroupUser.java ：

'pre> @Entity
公共类GroupUser实现Serializable {
@Id
@ManyToOne
@JoinColumn（ name =Group_id）
私人群组;

@Id
@ManyToOne
@JoinColumn（name =User_id）
私人用户用户;

@Id
@Column
private String s;

@Column
private int i;
}


以下是MySQL所说的：

  USER GROUP_USER GROUP 
 ------ ---------------------- --- --- 
 id User_id（PK，NOT NULL）id 
 Group_id（PK，NOT NULL）
s（PK，NOT NULL）
i（DEFAULT NULL）
  

GROUP_USER 详情：

• PRIMARY KEY：User_id，Group_id，s


• INDEX＃1 / FOREIGN KEY：User_id


• INDEX＃2 / FOREIGN KEY：Group_id

---

I还做了一些其他的测试，例如：

pre $ @Entity
public class A implements Serializable {

@Id
@Column
String a;

@Id
@Column
字符串b;

@Column
String c;






像一个魅力一样！

---

是否仍然有理由使用 @EmbeddedId 或 @ IdClass ？

并且：这是JPA 2.1还是Hibernate特性的一部分？

I don't know since when this is possible, but I just created composite keys the way I always wanted: No @EmbeddedId and no @IdClass required!!

• Spring 4.0.0.M3
• Hibernate 4.3.0.Beta4
• JPA 2.1

User.java:

@Entity
public class User {
    @Id
    ...

    @OneToMany(mappedBy="user", cascade=CascadeType.ALL, orphanRemoval=true)
    private List<GroupUser> groupUsers;     
}

Group.java:

@Entity
public class Group {
    @Id
    ...

    @OneToMany(mappedBy="user", cascade=CascadeType.ALL, orphanRemoval=true)
    private List<GroupUser> groupUsers;     
}

GroupUser.java:

@Entity
public class GroupUser implements Serializable {
    @Id
    @ManyToOne
    @JoinColumn(name="Group_id")
    private Group group;

    @Id
    @ManyToOne
    @JoinColumn(name="User_id")
    private User user;

    @Id
    @Column
    private String s;

    @Column
    private int i;
}

And here is what MySQL says:

 USER             GROUP_USER            GROUP
------    -------------------------    -------
 id        User_id  (PK, NOT NULL)       id 
           Group_id (PK, NOT NULL)
           s        (PK, NOT NULL)
           i        (DEFAULT NULL)

GROUP_USER details:

• PRIMARY KEY: User_id, Group_id, s
• INDEX #1 / FOREIGN KEY: User_id
• INDEX #2 / FOREIGN KEY: Group_id

---

I also did some other tests, like this:

@Entity
public class A implements Serializable {

    @Id
    @Column
    String a;

    @Id
    @Column
    String b;

    @Column
    String c;

}

Works like a charm!!

---

Is there still any reason to use @EmbeddedId or @IdClass?

And: Is this part of JPA 2.1 or an Hibernate feature?

解决方案

JPA requires a primary key class of some sort be defined for composite primary keys. In practice though, this seems required mostly for the EntityManager find and getReference calls that require a pk class instance. Implementations may have their own pk representation that you can use for these calls, but will not be portable.

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