为了满足您的要求，您可以将@ManyToMany 映射为@OneToMany 映射。
这样，USER_ROLE 将同时包含 USER_ID 和 ROLE_ID 作为复合主键
我会告诉你如何：
@Entity
@Table(name="USER")
public class User {
@Id
@GeneratedValue
private Integer id;
@OneToMany(cascade=CascadeType.ALL, mappedBy="joinedUserRoleId.user")
private List<JoinedUserRole> joinedUserRoleList = new ArrayList<JoinedUserRole>();
// no-arg required constructor
public User() {}
public User(Integer id) {
this.id = id;
}
// addRole sets up bidirectional relationship
public void addRole(Role role) {
// Notice a JoinedUserRole object
JoinedUserRole joinedUserRole = new JoinedUserRole(new JoinedUserRole.JoinedUserRoleId(this, role));
joinedUserRole.setUser(this);
joinedUserRole.setRole(role);
joinedUserRoleList.add(joinedUserRole);
}
}
@Entity
@Table(name="USER_ROLE")
public class JoinedUserRole {
public JoinedUserRole() {}
public JoinedUserRole(JoinedUserRoleId joinedUserRoleId) {
this.joinedUserRoleId = joinedUserRoleId;
}
@ManyToOne
@JoinColumn(name="USER_ID", insertable=false, updatable=false)
private User user;
@ManyToOne
@JoinColumn(name="ROLE_ID", insertable=false, updatable=false)
private Role role;
@EmbeddedId
// Implemented as static class - see bellow
private JoinedUserRoleId joinedUserRoleId;
// required because JoinedUserRole contains composite id
@Embeddable
public static class JoinedUserRoleId implements Serializable {
@ManyToOne
@JoinColumn(name="USER_ID")
private User user;
@ManyToOne
@JoinColumn(name="ROLE_ID")
private Role role;
// required no arg constructor
public JoinedUserRoleId() {}
public JoinedUserRoleId(User user, Role role) {
this.user = user;
this.role = role;
}
public JoinedUserRoleId(Integer userId, Integer roleId) {
this(new User(userId), new Role(roleId));
}
@Override
public boolean equals(Object instance) {
if (instance == null)
return false;
if (!(instance instanceof JoinedUserRoleId))
return false;
final JoinedUserRoleId other = (JoinedUserRoleId) instance;
if (!(user.getId().equals(other.getUser().getId())))
return false;
if (!(role.getId().equals(other.getRole().getId())))
return false;
return true;
}
@Override
public int hashCode() {
int hash = 7;
hash = 47 * hash + (this.user != null ? this.user.hashCode() : 0);
hash = 47 * hash + (this.role != null ? this.role.hashCode() : 0);
return hash;
}
}
}
记住
如果一个对象有一个赋值
标识符或复合键，
标识符应该分配给
调用 save() 之前的对象实例。
所以我们创建了一个像这样的 JoinedUserRoleId 构造函数来处理它
public JoinedUserRoleId(User user, Role role) {
this.user = user;
this.role = role;
}
最后是角色类
@Entity
@Table(name="ROLE")
public class Role {
@Id
@GeneratedValue
private Integer id;
@OneToMany(cascade=CascadeType.ALL, mappedBy="JoinedUserRoleId.role")
private List<JoinedUserRole> joinedUserRoleList = new ArrayList<JoinedUserRole>();
// no-arg required constructor
public Role() {}
public Role(Integer id) {
this.id = id;
}
// addUser sets up bidirectional relationship
public void addUser(User user) {
// Notice a JoinedUserRole object
JoinedUserRole joinedUserRole = new JoinedUserRole(new JoinedUserRole.JoinedUserRoleId(user, this));
joinedUserRole.setUser(user);
joinedUserRole.setRole(this);
joinedUserRoleList.add(joinedUserRole);
}
}
根据测试，我们写如下
User user = new User();
Role role = new Role();
// code in order to save a User and a Role
Session session = HibernateUtil.getSessionFactory().openSession();
session.beginTransaction();
Serializable userId = session.save(user);
Serializable roleId = session.save(role);
session.getTransaction().commit();
session.clear();
session.close();
// code in order to set up bidirectional relationship
Session anotherSession = HibernateUtil.getSessionFactory().openSession();
anotherSession.beginTransaction();
User savedUser = (User) anotherSession.load(User.class, userId);
Role savedRole = (Role) anotherSession.load(Role.class, roleId);
// Automatic dirty checking
// It will set up bidirectional relationship
savedUser.addRole(savedRole);
anotherSession.getTransaction().commit();
anotherSession.clear();
anotherSession.close();
注意根据上面的代码NO REFERENCE to JoinedUserRole 类。
如果您想检索 JoinedUserRole，请尝试以下操作
Session session = HibernateUtil.getSessionFactory().openSession();
session.beginTransaction();
Integer userId;
Integer roleId;
// Lets say you have set up both userId and roleId
JoinedUserRole joinedUserRole = (JoinedUserRole) session.get(JoinedUserRole.class, new JoinedUserRole.JoinedUserRoleId(userId, roleId));
// some operations
session.getTransaction().commit();
session.clear();
session.close();
问候，