java 没有单独的连接表的休眠@OneToMany
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Hibernate @OneToMany without a separate join table
提问by niklassaers
Consider the following database schema:
考虑以下数据库架构：
create table UserGroup ( id int not null auto_increment, name varchar(200),
primary key(id));
create table User ( id int not null auto_increment, name varchar(200),
groupId int not null, primary key(id));
User.groupId = UserGroup.id, so a user can only be a member of one group, but a usergroup can exist of many users. Fine so far, let's make the entities in Hibernate. Here's User:
User.groupId = UserGroup.id，所以一个用户只能是一个组的成员，但一个用户组可以存在多个用户。到此为止，让我们在 Hibernate 中创建实体。这是User：
@Entity
@Table(name = "User")
public class User {
@Id
@Column(name="id", nullable = false)
private Integer id;
@Column(name="name", length = 200, nullable = true)
private String name;
@ManyToOne(fetch=FetchType.EAGER)
@JoinColumn(name = "groupId", nullable = false, insertable=false, updatable=false)
@ForeignKey(name="FK_GroupId")
private UserGroup userGroup;
/* Getters, Setters, toString, equals & hashCode */
}
Here's UserGroup:
这是UserGroup：
@Entity
@Table(name = "UserGroup")
public class UserGroup {
@Id
@Column(name="id", nullable = false)
private Integer id;
@Column(name="name", length = 200, nullable = true)
private String name;
@OneToMany(fetch=FetchType.EAGER)
private List<User> users;
/* Getters, Setters, toString, equals & hashCode */
}
Now I'll get an error "Table mydb.usergroup_user' doesn't exist"because it expects a join-table. My data structure is "set in stone" due to interoperability with other applications that this application will replace, so I won't be making a join-table. Also, it should not be needed. How can I make a List<User> usersthat simply is a list of User where User.groupId == UserGroup.Id?
现在我会得到一个错误，"Table mydb.usergroup_user' doesn't exist"因为它需要一个连接表。由于与该应用程序将替换的其他应用程序的互操作性，我的数据结构是“一成不变的”，因此我不会制作连接表。此外，它不应该被需要。我怎样才能制作一个List<User> users简单的用户列表User.groupId == UserGroup.Id？
回答by Brian Yarger
I think you need the mappedBy="UserGroup"in the @OneToManyannotation.
我认为你需要mappedBy="UserGroup"的@OneToMany注释。
