HIbernate逐渐入门02—一对一,一对多,多对多映射

清疚 2023-01-02 05:22 69阅读 0赞

今天研究生了下一对一，一对多，多对多三种方式在Jpa中如何实用  
一.一对一

@Data
    @Entity
    @Table(name = "user")
    public class User { 
        @Id
        @GeneratedValue
        private Long id;
        private String name;
        //开启级联操作
        @OneToOne(cascade = CascadeType.PERSIST)
        private Student student;
    }

@Data
    @Entity
    @Table(name = "student")
    public class Student { 
        @Id
        @GeneratedValue
        private Long id;
        private String name;
    }

这样就完成了一对一的关系映射

二.一对多

@Data
    @Entity
    @Table(name = "user")
    public class User { 
        @Id
        @GeneratedValue
        private Long id;
        private String name;
        @OneToMany(mappedBy = "user",cascade=CascadeType.ALL,fetch=FetchType.LAZY)
        //级联保存、更新、删除、刷新;延迟加载。当删除用户，会级联删除该用户的所有文章
        //拥有mappedBy注解的实体类为关系被维护端
        //mappedBy="author"中的author是Article中的author属性
        private List<Article> articleList;//文章列表
    }

@Data
    @Entity
    @Table(name = "article")
    public class Article { 
        @Id
        @GeneratedValue
        private Long id;
        private String name;
        @ManyToOne(cascade={ CascadeType.MERGE,CascadeType.REFRESH},optional=false)//可选属性optional=false,表示author不能为空。删除文章，不影响用户
        @JoinColumn(name="user_id")//设置在article表中的关联字段(外键)
        private User user;//所属作者
    }

这样就完成了一对多的关系映射

三.多对多

@Data
    @Entity
    @Table(name = "user")
    public class User { 
        @Id
        @GeneratedValue
        private Long id;
        private String name;
        @ManyToMany
        @JoinTable(name = "user_authority",joinColumns = @JoinColumn(name = "user_id"),
                inverseJoinColumns = @JoinColumn(name = "authority_id"))
        //1、关系维护端，负责多对多关系的绑定和解除
        //2、@JoinTable注解的name属性指定关联表的名字，joinColumns指定外键的名字，关联到关系维护端(User)
        //3、inverseJoinColumns指定外键的名字，要关联的关系被维护端(Authority)
        //4、其实可以不使用@JoinTable注解，默认生成的关联表名称为主表表名+下划线+从表表名，
        //即表名为user_authority
        //关联到主表的外键名：主表名+下划线+主表中的主键列名,即user_id
        //关联到从表的外键名：主表中用于关联的属性名+下划线+从表的主键列名,即authority_id
        //主表就是关系维护端对应的表，从表就是关系被维护端对应的表
        private List<Authority> authorityList;
    }

@Data
    @Entity
    public class Authority { 
        @Id
        @GeneratedValue(strategy = GenerationType.IDENTITY)
        private Integer id;
        @Column(nullable = false)
        private String name; //权限名
        @ManyToMany(mappedBy = "authorityList")
        private List<User> userList;
    }

这样就完成了多对多的关系映射

另外我们在测试时需要两个类来继承jpa原有的方法

@Repository
    public interface UserRepository extends
            JpaRepository<User,Integer>, JpaSpecificationExecutor<User> { 
    }

public interface AuthorityRepository extends
            JpaRepository<Authority,Integer>, JpaSpecificationExecutor<Authority> { 
    }

测试代码

@Service
    public class UserService { 
        @Autowired
        private UserRepository UserRepository;
        @Autowired
        private AuthorityRepository authorityRepository;
        public void Insert() { 
        	//一对一测试 一对多测试
            User aa=new User();
            aa.setName("aaa");;
            Student bb=new Student();
            bb.setName("bb");
            Article a1=new Article();
            Article a2=new Article();
            a1.setName("cc");
            a2.setName("dd");
            a1.setUser(aa);
            a2.setUser(aa);
            List<Article> s = new ArrayList<>();
            s.add(a1);
            s.add(a2);
            aa.setArticleList(s);
            aa.setStudent(bb);
            UserRepository.save(aa);
    		
    		//一对多测试
            Authority authority = new Authority();
            Authority authority2 = new Authority();
            authority.setName("ROLE_ADMIN");
            authority2.setName("2222");
            authorityRepository.save(authority);
            authorityRepository.save(authority2);
            User user = new User();
            user.setName("admin");
            List<Authority> authorityList = new ArrayList<>();
            authorityList.add(authority);
            authorityList.add(authority2);
            user.setAuthorityList(authorityList);
            UserRepository.save(user);
        }
    }

如下图，所有数据已经被存储进去  
![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3dlaXhpbl80NDcxNDgwOA_size_16_color_FFFFFF_t_70]

[watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3dlaXhpbl80NDcxNDgwOA_size_16_color_FFFFFF_t_70]: /images/20221120/0ef6a272c8324140b5b70f2aaacccc3a.png