Mybatis使用注解实现复杂关系映射开发

约定不等于承诺〃 2023-07-18 09:56 114阅读 0赞

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实现复杂关系映射之前我们可以在映射文件中通过配置来实现，在使用注解开发时我们需要借 助@Results 注解，@Result 注解，@One 注解，@Many 注解。

**@Results** **注解 代替的是标签**\*\*\*\*

该注解中可以使用单个@Result 注解，也可以使用@Result 集合

@Results（\{@Result（），@Result（）\}）或@Results（@Result（））

@Resutl 注解

**代替了** **标签和****标签**

**@Result** **中 属性介绍：** id 是否是主键字段 column 数据库的列名

property 需要装配的属性名

one 需要使用的@One 注解（@Result（one=@One）（）））

many 需要使用的@Many 注解（@Result（many=@many）（）））

**@One** **注解（一对一） 代替了**\*\*\*\***标签，是多表查询的关键，在注解中用来指定子查询返回单一对象。**

**@One** **注解属性介绍：**

**select** **指定用来多表查询的** **sqlmapper**

fetchType 会覆盖全局的配置参数 lazyLoadingEnabled。。 使用格式：

@Result(column=" “,property=”",one=@One(select=""))

**@Many** **注解（多对一）**

**代替了**\*\*<**Collection**>**标签**,\*\***是是多表查询的关键，在注解中用来指定子查询返回对象集合。**

注意：聚集元素用来处理“一对多”的关系。需要指定映射的 Java 实体类的属性，属性的 javaType

（一般为 ArrayList）但是注解中可以不定义； 使用格式：

@Result(property="",column="",many=@Many(select=""))

### 添加 User 实体类 ###

public class User implements Serializable { 
        private Integer userid;
        private String userName;
        private String userAddress;
        private String userSex;
        private Date userBirthday;
        private List<Account> accounts;
    
        public List<Account> getAccounts() { 
            return accounts;
        }
    
        public void setAccounts(List<Account> accounts) { 
            this.accounts = accounts;
        }
    
        public Integer getUserid() { 
            return userid;
        }
    
        public void setUserid(Integer userid) { 
            this.userid = userid;
        }
    
        public String getUserName() { 
            return userName;
        }
    
        public void setUserName(String userName) { 
            this.userName = userName;
        }
    
        public String getUserAddress() { 
            return userAddress;
        }
    
        public void setUserAddress(String userAddress) { 
            this.userAddress = userAddress;
        }
    
        public String getUserSex() { 
            return userSex;
        }
    
        public void setUserSex(String userSex) { 
            this.userSex = userSex;
        }
    
        public Date getUserBirthday() { 
            return userBirthday;
        }
    
        public void setUserBirthday(Date userBirthday) { 
            this.userBirthday = userBirthday;
        }
    
        @Override
        public String toString() { 
            return "User{" +
                    "userid=" + userid +
                    ", userName='" + userName + '\'' +
                    ", userAddress='" + userAddress + '\'' +
                    ", userSex='" + userSex + '\'' +
                    ", userBirthday=" + userBirthday +
                    '}';
        }
    }

### 添加 Account 实体类 ###

public class Account implements Serializable { 
        private Integer id;
        private Integer uid;
        private Double money;
        private User user;
    
        public User getUser() { 
            return user;
        }
    
        public void setUser(User user) { 
            this.user = user;
        }
    
        public Integer getId() { 
            return id;
        }
    
        public void setId(Integer id) { 
            this.id = id;
        }
    
        @Override
        public String toString() { 
            return "Account{" +
                    "id=" + id +
                    ", uid=" + uid +
                    ", money=" + money +
                    '}';
        }
    
        public Integer getUid() { 
            return uid;
        }
    
        public void setUid(Integer uid) { 
            this.uid = uid;
        }
    
        public Double getMoney() { 
            return money;
        }
    
        public void setMoney(Double money) { 
            this.money = money;
        }
    }

#### 编写SQL语句 ####

SELECT
    account.*, user.username, user.address
    FROM
    account, user
    WHERE account.uid = user.id

#### 定义持久层接口 ####

@CacheNamespace(blocking = true)
    public interface  IUserDao { 
        @Select("select * from user")
        @Results(id = "userMap", value = { 
                @Result(id = true,column = "id",property = "userid"),
                @Result(column = "username",property = "userName"),
                @Result(column = "address",property = "userAddress"),
                @Result(column = "sex",property = "userSex"),
                @Result(column = "birthday",property = "userBirthday"),
                @Result(property = "accounts", column = "id",
                        many = @Many(select = "dao.IAccountDao.findAccountByUid",fetchType = FetchType.LAZY))
        })
        List<User> findAll();
    
    
        @Select("select * from user where id=#{id}")
        @ResultMap(value = { "userMap"})
        User findById(Integer userId);
    
        @Select("select * from user where username like #{username}")
        @ResultMap("userMap")
        List<User> findUserByName(String username);
    }

public interface IAccountDao { 
        @Select("select * from account")
        @Results(id = "accountMap", value={ 
                @Result(id = true,column = "id",property = "id"),
                @Result(column = "uid",property = "uid"),
                @Result(column = "money",property = "money"),
                @Result(property = "user",column = "uid",
                        one = @One(select="dao.IUserDao.findById",fetchType= FetchType.EAGER))
        })
        List<Account> findAll();
    
        @Select("select * from account where uid=#{userId}")
        List<Account> findAccountByUid(Integer userId);
    }

#### 编写测试类 ####

public class AccountTest { 
        private SqlSessionFactory factory;
        private SqlSession session;
        private IAccountDao accountDao;
        private InputStream in;
    
        @Before
        public void init()throws Exception{ 
            in= Resources.class.getResourceAsStream("/SqlMapConfig.xml");
            factory=new SqlSessionFactoryBuilder().build(in);
            session=factory.openSession();
            accountDao=session.getMapper(IAccountDao.class);
        }
        @After
        public void destroy()throws Exception{ 
            session.commit();
            session.close();
            in.close();
        }
    
    
        @Test
        public void testFindAll(){ 
            List<Account> accounts=accountDao.findAll();
            for (Account account : accounts) { 
                System.out.println("---");
                System.out.println(account);
                System.out.println(account.getUser());
            }
        }
    
    }