SpringBoot|SpringBoot + JPA @ManyToMany的操作要点说明 SpringBoot+JPA@ManyToMany的操作要点

SpringBoot + JPA @ManyToMany 要点

对应的Entity的建立
Junit的测试

JPA中ManyToMany关系问题

解决办法

SpringBoot + JPA @ManyToMany 要点这里主要时记录下此种方法的注意事项。
环境：mysql 引擎为innoDB ,否则没有事务的说法的。

#不加这句则默认为myisam引擎spring.jpa.database-platform=org.hibernate.dialect.MySQL5InnoDBDialect

对应的Entity的建立
此处注意不可使用lombok @Data 注解。使用@Setter 、@Getter注解。主要原因时要自己覆写hash() equals(),toString() 方法。这样添加和删除的时候不会出现异常。否则出现循环的引用，不能删除或stackOver；
User

@Setter@Getter@Entitypublic class User {@Id@GenericGenerator(name="jpauuid",strategy = "org.hibernate.id.UUIDGenerator")@GeneratedValue(generator = "jpauuid")@Column(length = 32,nullable = false)private Stringid; @Column(length = 30)private String username; @ManyToMany(cascade = CascadeType.REFRESH,mappedBy = "users")private Set roles; @Overridepublic boolean equals(Object o) {if (this == o) return true; if (o == null || getClass() != o.getClass()) return false; User user = (User) o; return id.equals(user.id) &&username.equals(user.username) &&roles.equals(user.roles); }@Overridepublic int hashCode() {return Objects.hash(id, username, roles); }@Overridepublic String toString() {return "User{" +"id='" + id + '\'' +", username='" + username + '\'' +", roles=" + roles +'}'; }}

Role

@Setter@Getter@Entitypublic class Role {@Id@GeneratedValue(strategy = GenerationType.AUTO)private Integer id; @Column(length = 30)private Stringname; @ManyToMany(cascade = CascadeType.REFRESH)@JoinTable(name = "user_role",joinColumns = @JoinColumn(name = "role_id"),inverseJoinColumns = @JoinColumn(name="user_id"))private Setusers; public void addUser(User user){this.users.add(user); }public void removeUser(User user){this.users.remove(user); }}

Junit的测试
注意@transaction的注解一定要加上。并且@Rollback(value = https://www.it610.com/article/false) 也加上。springboot-test 默认在内存中save,不提交，所有以通过了但是数据库中无内容，官方说为了不影响上下文环境。

/*** 添加角色*/@Testpublic void addRole(){Role role = new Role(); role.setName("系统管理员"); roleRepository.save(role); }/*** 添加用户*/@Testpublic void addUser() {User user = new User(); user.setUsername("test1"); userRepostitory.save(user); }/**** 通过关系维护方添加角色和用户的关系*/@Test@Transactional@Rollback(value = https://www.it610.com/article/false)public voidaddUserRole(){User user = userRepostitory.findByUsername("test1"); Role role = roleRepository.getOne(1); role.addUser(user); roleRepository.saveAndFlush(role); }/**** 删除对应的关联数据*/@Test@Transactionalpublic void removeRoleUser(){User user = userRepostitory.findByUsername("test1"); Role role = roleRepository.getOne(1); role.removeUser(user); roleRepository.saveAndFlush(role); }

不能删除和添加成功，出现循环的主要问题在 toString()方法。此方法只能包含基本的元素，不要包含相应的@ManyToMany 的对象。两个类都是。这样才会ok.

@RunWith(SpringRunner.class)@SpringBootTestpublic class DemoBeetlApplicationTests {@Autowiredprivate UserRepostitory userRepostitory; @Autowiredprivate RoleRepository roleRepository; @Autowiredprivate UserGroupRepository userGroupRepository; @Autowiredprivate PriviledgeRepository priviledgeRepository; @Autowiredprivate MenuRepository menuRepository; @Autowiredprivate FileRepository fileRepository; @Autowiredprivate ElementRepository elementRepository; @Autowiredprivate OperationRepository operationRepository; @Testpublic void contextLoads() {System.out.println("helle junit"); }/*** 添加角色*/@Testpublic void addRole(){Role role = new Role(); role.setName("系统管理员"); roleRepository.save(role); }/*** 添加用户*/@Testpublic void addUser() {User user = new User(); user.setUsername("test1"); userRepostitory.save(user); }/**** 通过关系维护方添加角色和用户的关系***/@Test@Transactional@Rollback(value = https://www.it610.com/article/false)public voidaddRoleUser(){User user = userRepostitory.findByUsername("test1"); Role role = roleRepository.getOne(2); role.addUser(user); roleRepository.saveAndFlush(role); }/**** 删除对应的关联数据*/@Test@Transactional@Rollback(value = https://www.it610.com/article/false)public void removeRoleUser(){Role role = roleRepository.getOne(2); User user = userRepostitory.findByUsername("test1"); role.removeUser(user); roleRepository.saveAndFlush(role); }/**** 删除单一的角色是可以删除相应的关系*/@Testpublic void removeRole(){Role role = roleRepository.getOne(2); roleRepository.delete(role); }/**** 删除用户不能联动删除关系,* 这个时不能执行的，只能在数据维护端来进行删除后，在进行相应的用户删除。**/@Testpublicvoid removeUser(){Role role = roleRepository.getOne(2); User user = userRepostitory.findByUsername("test1"); role.removeUser(user); userRepostitory.delete(user); }

JPA中ManyToMany关系问题配置JPA的时候多对多关系，报以下错误：

org.hibernate.AnnotationException: Illegal use of mappedBy on both sides of the relationship: com.csair.gme.core.domain.ComponentType.componentPropertys

解决办法
不能两边都用mappedBy，只能用一边，而且用mappedBy的那一边是从表，另外一边就是主表。mappedBy=‘主表里的变量名'
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