1. Create a package class corresponding to the database
User:
@Entity //实体类
@Table(name = "sys_user") //实体类对应数据库表名
public class User {
@Id //主键
@GeneratedValue(strategy = GenerationType.IDENTITY) //主键自增
@Column(name="user_id") //数据库对应列名
private Long userId;
@Column(name="user_name")
private String userName;
@Column(name="age")
private Integer age;
/**
* 配置用户到角色的多对多关系
* 配置多对多的映射关系
* 1.声明表关系的配置
* @ManyToMany(targetEntity = Role.class) //多对多
* targetEntity：代表对方的实体类字节码
* 2.配置中间表（包含两个外键）
* @JoinTable
* name: 中间表的名称
* joinColumns：配置当前对象在中间表的外键
* @JoinColumn的数组
* name：外键名
* referencedColumnName：参照的主表的主键名
* inverseJoinColumns：配置对方对象在中间表的外键
*/
@ManyToMany(targetEntity = Role.class)
@JoinTable(name = "sys_user_role", //中间表
//joinColumns, 当前对象在中间表中的外键
joinColumns = {@JoinColumn(name = "sys_user_id", referencedColumnName = "user_id")},
//inverseJoinColumns，对方对象在中间表的外键
inverseJoinColumns = {@JoinColumn(name = "sys_role_id", referencedColumnName = "role_id")}
)
private Set<Role> roles = new HashSet();
//getter setter 方法....
//toString() 方法....
}Role:
@Entity //实体类
@Table(name = "sys_role") //实体类对应数据库表名
public class Role {
@Id //主键
@GeneratedValue(strategy = GenerationType.IDENTITY) //主键自增
@Column(name = "role_id") //数据库对应列名
private Long roleId;
@Column(name = "role_name")
private String roleName;
@ManyToMany(targetEntity = User.class)
@JoinTable(name = "sys_user_role", //中间表
//joinColumns, 当前对象在中间表中的外键
joinColumns = {@JoinColumn(name = "sys_role_id", referencedColumnName = "role_id")},
//inverseJoinColumns，对方对象在中间表的外键
inverseJoinColumns = {@JoinColumn(name = "sys_user_id", referencedColumnName = "user_id")}
)
private Set<User> users = new HashSet();
//getter setter 方法....
//toString() 方法....
}2. Create a dao layer interface specification that conforms to SpringDataJpa
UserDao:
public interface UserDao extends JpaRepository<User, Long>, JpaSpecificationExecutor<User> {
}RoleDao:
public interface RoleDao extends JpaRepository<Role, Long>, JpaSpecificationExecutor<Role> {
}Three. Write the test class
Write a test framework:
@RunWith(SpringJUnit4ClassRunner.class)
@ContextConfiguration(locations = "classpath:applicationContext.xml")
public class ManyToManyTest {
@Autowired
private UserDao userDao;
@Autowired
private RoleDao roleDao;
}1. Save a user while saving the role associated with the user
@Test
@Transactional
@Rollback(false)
public void testAdd() {
//创建一个用户
User user = new User();
user.setUserName("小李");
user.setAge(18);
//用户关联的角色
Role role = new Role();
role.setRoleName("java程序员");
//配置用户到角色关系，可以对中间表中的数据进行维护
user.getRoles().add(role);
//配置角色到用户的关系，可以对中间表的数据进行维护
role.getUsers().add(user);
userDao.save(user);
roleDao.save(role);
}At runtime, the intermediate table will be processed twice, causing an exception to be thrown. Here you need to give up the rights protection processing: the passive party (role) gives up.
Modify the Role package class:
*** The value of mappedBy is a member variable of Role defined in the User package class
@ManyToMany(mappedBy = "roles") //配置多表关系
private Set<User> users = new HashSet();2. Cascade add (add the user while adding the user's corresponding role)
Modify the User package class:
* Modify the annotation on the member attribute in the User package class:
(CascadeType.ALL is to cascade all operations)
(CascadeType.MERGE is a cascading update operation)
(CascadeType.PERSIST is a cascade save operation)
(CascadeType.REMOVE is a cascade delete operation)
@ManyToMany(targetEntity = Role.class, cascade = CascadeType.ALL)
@JoinTable(name = "sys_user_role", //中间表
//joinColumns, 当前对象在中间表中的外键
joinColumns = {@JoinColumn(name = "sys_user_id", referencedColumnName = "user_id")},
//inverseJoinColumns，对方对象在中间表的外键
inverseJoinColumns = {@JoinColumn(name = "sys_role_id", referencedColumnName = "role_id")}
)Define the method of cascading addition:
@Test
@Transactional
@Rollback(false)
public void testCasCadeAdd() {
//创建一个用户
User user = new User();
user.setUserName("小王");
user.setAge(28);
//用户关联的角色
Role role = new Role();
role.setRoleName("产品经理");
//配置用户到角色关系，可以对中间表中的数据进行维护
user.getRoles().add(role);
//配置角色到用户的关系，可以对中间表的数据进行维护
role.getUsers().add(user);
userDao.save(user);
}Define the method of cascading delete:
@Test
@Transactional
@Rollback(false)
public void testCasCadeRemove() {
//查询1号用户
User user = userDao.findOne(1L);
//删除1号用户
userDao.delete(user);
}
Source code download: https://pan.baidu.com/s/1lqRG8mPJet2IxbGZHsJcqg