[英]how to make a composite primary key (java persistence annotation)
如何使表user_roles将两列(userID,roleID)定义为复合主键。 应该很容易,只是记不住/找不到。
在user
实体中:
@ManyToMany(fetch = FetchType.LAZY)
@JoinTable(name = "user_roles")
public List<RoleDAO> getRoles() {
return roles;
}
@Id
@GeneratedValue(strategy = GenerationType.AUTO)
public Integer getUserID() {
return userID;
}
在roles
实体中:
@ManyToMany(fetch = FetchType.LAZY)
@JoinTable(name = "user_roles")
public List<UserDAO> getUsers() {
return users;
}
@Id
@GeneratedValue(strategy = GenerationType.AUTO)
public Integer getRoleID() {
return roleID;
}
谢谢。
** 更多信息
因此,第三个表user_roles
(由上面自动生成)从user
实体获取userID
,从roles
实体获取roleID
。 现在我需要生成的表( user_roles
)中的这两列作为复合主键。
你已经在这里找到了一些关于如何完全按照你的要求做出的好答案。
作为参考,我只想提一下在Hibernate中这样做的推荐方法,即使用代理键作为主键,并将业务键标记为NaturalId:
虽然我们建议使用代理键作为主键,但您应该尝试识别所有实体的自然键。 自然键是属性或属性的组合,它们是唯一且非空的。 它也是不可改变的。 映射元素内的自然键的属性。 Hibernate将生成必要的唯一键和可空性约束,因此,您的映射将更加自我记录。
建议您实现equals()和hashCode()以比较实体的自然键属性。
在代码中,使用注释,这看起来像这样:
@Entity
public class UserRole {
@Id
@GeneratedValue
private long id;
@NaturalId
private User user;
@NaturalId
private Role role;
}
使用它可以为您节省很多麻烦,因为您会发现您经常需要引用/映射组合主键。
我发现这很困难,最后只是放弃了与Hibernate的斗争,而是决定顺其自然。 我完全明白,在您的情况下这可能是不可能的,因为您可能正在处理遗留软件或依赖项,但我只是想提及它以供将来参考。 ( 如果你不能使用它也许其他人可以 !)
为了满足您的要求,您可以将@ManyToMany映射为@OneToMany映射。 这样,USER_ROLE将包含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;
}
}
}
记得
如果对象具有指定的标识符或复合键,则在调用save()之前,应该将标识符分配给对象实例。
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Role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);
}
}
根据测试它,让我们写下面的内容
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();
请注意根据以上代码无参考JoinedUserRole类。
如果要检索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,
复合键是使用@IdClass完成的(另一种方式是使用@EmbeddedId和@Embeddable,不确定你要查找哪一个)@IdClass如下
@Entity
@IdClass(CategoryPK.class)
public class Category {
@Id
protected String name;
@Id
protected Date createDate;
}
public class CategoryPK implements Serializable {
String name;
Date createDate;
public boolean equals(object other) {
//implement a equals that the PP can use to determine
//how the CategoryPK object can be identified.
}
public int hashCode(){
return Super.hashCode();
}
}
我的类别将是您的user_roles,名称和createDate将是您的用户ID和角色
感谢您改进您的问题......并考虑到这些建议。
(对不起,你用Daos后缀你的实体有点奇怪,但这不是重点。)
我不确定还有什么问题:
我对主键有同样的问题。 我也知道@Embeddable和@EmbeddedId类的解决方案。 但我只想要带注释的简单解决方案。
我通过这篇文章找到了启示: http : //www.vaannila.com/hibernate/hibernate-example/hibernate-mapping-many-to-many-using-annotations-1.html
这是魔术:
这会在连接表上生成主键:
@ManyToMany(cascade = CascadeType.ALL)
@JoinTable(name="classA_classB")
private Set<ClassA> classesA;
这不会在连接表上生成主键:
@ManyToMany(cascade = CascadeType.ALL)
@JoinTable(name="classA_classB")
private List<ClassA> classesA;
至少在我的环境中
请注意,区别在于使用Set或List
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