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注解说明

• @OneToMany:

  作用：建立一对多的关系映射
  属性：
  targetEntityClass：指定多的多方的类的字节码
  mappedBy：指定从表实体类中引用主表对象的名称。
  cascade：指定要使用的级联操作
  fetch：指定是否采用延迟加载
  orphanRemoval：是否使用孤儿删除

• @ManyToOne

  作用：建立多对一的关系
  属性：
  targetEntityClass：指定一的一方实体类字节码
  cascade：指定要使用的级联操作
  fetch：指定是否采用延迟加载
  optional：关联是否可选。如果设置为false，则必须始终存在非空关系。

• @JoinColumn

  作用：用于定义主键字段和外键字段的对应关系。
  属性：
  name：指定外键字段的名称
  referencedColumnName：指定引用主表的主键字段名称
  unique：是否唯一。默认值不唯一
  nullable：是否允许为空。默认值允许。
  insertable：是否允许插入。默认值允许。
  updatable：是否允许更新。默认值允许。
  columnDefinition：列的定义信息。

实体类

package pers.zhang.entity;import javax.persistence.*;import java.util.HashSet;import java.util.Set;/** * @author zhang * @date 2019/12/17 - 22:32 */@Entity@Table(name = "sys_user")public class User {
       @Id    @GeneratedValue(strategy = GenerationType.IDENTITY)    @Column(name = "user_id")    private Long userId;    @Column(name = "user_name")    private String userName;    @Column(name = "age")    private Integer age;    public Long getUserId() {
           return userId;    }    /*        配置用户到角色的多对多关系            1. 声明表关系                @ManyToMany(targetEntity = Role.class)                       targetEntity:对方实体类的字节码            2. 配置中间表（包含两个外键）                JoinTable                    name:中间表名                    joinColumns：当前表在中间表中的外键                    inverseJoinColumns：对方表在中间表的外键     */    @ManyToMany(targetEntity = Role.class, cascade = CascadeType.ALL)    @JoinTable(name = "sys_user_role",                joinColumns = {
   @JoinColumn(name = "sys_user_id", referencedColumnName = "user_id")},                inverseJoinColumns = {
   @JoinColumn(name = "sys_role_id", referencedColumnName = "role_id")})    private Set
   
     roles = new HashSet<>();    public Set
    
      getRoles() {
           return roles;    }    public void setRoles(Set
     
       roles) {
           this.roles = roles;    }    public void setUserId(Long userId) {
           this.userId = userId;    }    public String getUserName() {
           return userName;    }    public void setUserName(String userName) {
           this.userName = userName;    }    public Integer getAge() {
           return age;    }    public void setAge(Integer age) {
           this.age = age;    }}
     
    
   

package pers.zhang.entity;import javax.persistence.*;import java.util.HashSet;import java.util.Set;/** * @author zhang * @date 2019/12/17 - 22:32 */@Entity@Table(name = "sys_role")public class Role {
       @Id    @GeneratedValue(strategy = GenerationType.IDENTITY)    @Column(name = "role_id")    private Long roleId;    @Column(name = "role_name")    private String roleName;//    @ManyToMany(targetEntity = User.class)//    @JoinTable(name = "sys_user_role",//            joinColumns = {@JoinColumn(name = "sys_role_id", referencedColumnName = "user_id")},//            inverseJoinColumns = {@JoinColumn(name = "sys_user_id", referencedColumnName = "role_id")})    @ManyToMany(mappedBy = "roles")    private Set
   
     users = new HashSet<>();    public Set
    
      getUsers() {
           return users;    }    public void setUsers(Set
     
       users) {
           this.users = users;    }    public Long getRoleId() {
           return roleId;    }    public void setRoleId(Long roleId) {
           this.roleId = roleId;    }    public String getRoleName() {
           return roleName;    }    public void setRoleName(String roleName) {
           this.roleName = roleName;    }}
     
    
   

Dao接口

package pers.zhang.dao;import org.springframework.data.jpa.repository.JpaRepository;import org.springframework.data.jpa.repository.JpaSpecificationExecutor;import pers.zhang.entity.Role;/** * @author zhang * @date 2019/12/17 - 22:37 */public interface RoleDao extends JpaRepository
   
    , JpaSpecificationExecutor
    
      {
   }
    
   

package pers.zhang.dao;import org.springframework.data.jpa.repository.JpaRepository;import org.springframework.data.jpa.repository.JpaSpecificationExecutor;import pers.zhang.entity.User;/** * @author zhang * @date 2019/12/17 - 22:37 */public interface UserDao extends JpaRepository
   
    , JpaSpecificationExecutor
    
      {
   }
    
   

测试类

package pers.zhang;import org.junit.Test;import org.junit.runner.RunWith;import org.springframework.beans.factory.annotation.Autowired;import org.springframework.test.annotation.Rollback;import org.springframework.test.context.ContextConfiguration;import org.springframework.test.context.junit4.SpringJUnit4ClassRunner;import org.springframework.transaction.annotation.Transactional;import pers.zhang.dao.RoleDao;import pers.zhang.dao.UserDao;import pers.zhang.entity.Role;import pers.zhang.entity.User;/** * @author zhang * @date 2019/12/17 - 23:04 */@RunWith(SpringJUnit4ClassRunner.class)@ContextConfiguration(locations = "classpath:applicationContext.xml")public class Many2ManyTest {
       @Autowired    UserDao userDao;    @Autowired    RoleDao roleDao;    /*        保存一个用户，保存一个角色            多对多放弃维护权：谁被选择谁放弃维护权     */    @Test    @Transactional    @Rollback(false)    public void testAdd(){
           User user = new User();        user.setUserName("小李");        Role role = new Role();        role.setRoleName("Java程序员");        //User方维护多对多关系        user.getRoles().add(role);        userDao.save(user);        roleDao.save(role);        /*            Hibernate: insert into sys_user (age, user_name) values (?, ?)            Hibernate: insert into sys_role (role_name) values (?)            Hibernate: insert into sys_user_role (sys_user_id, sys_role_id) values (?, ?)         */    }    /*        级联操作：保存一个用户的同时保存用户关联的角色     */    @Test    @Transactional    @Rollback(false)    public void testCascadeAdd(){
           User user = new User();        user.setUserName("小王");        Role role = new Role();        role.setRoleName("C#程序员");        //User方维护多对多关系        user.getRoles().add(role);        userDao.save(user);        /*            Hibernate: insert into sys_user (age, user_name) values (?, ?)            Hibernate: insert into sys_role (role_name) values (?)            Hibernate: insert into sys_user_role (sys_user_id, sys_role_id) values (?, ?)         */    }    /*        级联删除：删除一个用户同时删除关联的角色     */    @Test    @Transactional    @Rollback(false)    public void testCascaseDelete(){
           User user = userDao.findOne(1L);        userDao.delete(user);        /*            Hibernate: select user0_.user_id as user_id1_3_0_, user0_.age as age2_3_0_, user0_.user_name as user_nam3_3_0_ from sys_user user0_ where user0_.user_id=?            Hibernate: select roles0_.sys_user_id as sys_user1_4_0_, roles0_.sys_role_id as sys_role2_4_0_, role1_.role_id as role_id1_2_1_, role1_.role_name as role_nam2_2_1_ from sys_user_role roles0_ inner join sys_role role1_ on roles0_.sys_role_id=role1_.role_id where roles0_.sys_user_id=?            Hibernate: delete from sys_user_role where sys_user_id=?            Hibernate: delete from sys_role where role_id=?            Hibernate: delete from sys_user where user_id=?         */    }}

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