jpa配置多对多关系(中间表)

水深无声 2022-05-28 09:55 759阅读 0赞

两个实体tb\_user,tb\_role  
现在我们再tb\_user或者tb\_role中任意一个里面进行维护关系，多对对的情况下我们需要创建一个中间表来完成这个关系的映射，我们再tb\_user中添加注解@ManyToMany然后再添加一个注解@JoinTable因为我们是要创建中间表所以要使用这个注解。JoinTable注解中我们添加如下例子中的内容，joinColumns当前表中的字段在中间表中的字段名称，inverseJoinColumns关联的外键表在中间表中的字段名称

@Entity
    @Table(name = "tb_user")
    @SequenceGenerator(name = "tb_user_sq",sequenceName = "tb_user_sqe")
    public class TbUser extends BaseEntity{ 
    
    
        /** * 用户名 */
        private String userName;
        /** * 登录名 */
        private String loginName;
        /** * 登陆密码 */
        private String passWord;
        /** * 手机号 */
        private String telPhone;
        /** * 一个用户可以有多个角色 */
        private List<TbRole> tbRoleList=new ArrayList<>();
    
        public String getUserName() {
            return userName;
        }
    
        public void setUserName(String userName) {
            this.userName = userName;
        }
    
        public String getLoginName() {
            return loginName;
        }
    
        public void setLoginName(String loginName) {
            this.loginName = loginName;
        }
    
        public String getPassWord() {
            return passWord;
        }
    
        public void setPassWord(String passWord) {
            this.passWord = passWord;
        }
    
        public String getTelPhone() {
            return telPhone;
        }
    
        public void setTelPhone(String telPhone) {
            this.telPhone = telPhone;
        }
    
        @Id
        @Override
        @GeneratedValue(generator = "tb_user_sq",strategy = GenerationType.SEQUENCE)
        public Long getId() {
            return this.id;
        }
        @ManyToMany(cascade = CascadeType.REMOVE,fetch = FetchType.LAZY)
        @JoinTable(name = "tb_user_role",joinColumns = @JoinColumn(name="tb_user_id",referencedColumnName = "id"),inverseJoinColumns = @JoinColumn(name = "tb_role_id",referencedColumnName = "id"))
        public List<TbRole> getTbRoleList() {
            return tbRoleList;
        }
    
        public void setTbRoleList(List<TbRole> tbRoleList) {
            this.tbRoleList = tbRoleList;
        }
    }

因为在tb\_user中我们维护了两个表的关系，所以如果我们在tb\_role中如果不想创建关联字段的话就不用添加tbUser的关系字段

@Entity
    @Table(name = "tb_role")
    @SequenceGenerator(name = "tb_role_sq",sequenceName = "tb_role_sqe")
    public class TbRole extends BaseEntity{ 
    
    
        @Override
        @Id
        @GeneratedValue(generator = "tb_role_sq",strategy = GenerationType.SEQUENCE)
        public Long getId() {
            return this.id;
        }
    
        private String roleName;
    
    
        @ManyToMany(mappedBy = "tbRoleList")
        public String getRoleName() {
            return roleName;
        }
    
        public void setRoleName(String roleName) {
            this.roleName = roleName;
        }
    }

如果想要在tb\_role中进行维护关联字段的话如下，我们在字段中添加注解 @ManyToMany然后使用直接属性mappedBy值是当前表在关联表中的字段名称

@Entity
    @Table(name = "tb_role")
    @SequenceGenerator(name = "tb_role_sq",sequenceName = "tb_role_sqe")
    public class TbRole extends BaseEntity{ 
    
    
        @Override
        @Id
        @GeneratedValue(generator = "tb_role_sq",strategy = GenerationType.SEQUENCE)
        public Long getId() {
            return this.id;
        }
    
        private String roleName;
    
        private List<TbUser> tbUserList=new ArrayList<>();
    
        public String getRoleName() {
            return roleName;
        }
    
        public void setRoleName(String roleName) {
            this.roleName = roleName;
        }
        @ManyToMany(mappedBy = "tbRoleList")
        public List<TbUser> getTbUserList() {
            return tbUserList;
        }
    
        public void setTbUserList(List<TbUser> tbUserList) {
            this.tbUserList = tbUserList;
        }
    }