MyBatis之注解开发-6

6-Mybatis注解开发

6.1 MyBatis的常用注解

这几年来注解开发越来越流行，Mybatis也可以使用注解开发方式，这样我们就可以减少编写Mapper映射文件了。我们先围绕一些基本的CRUD来学习，再学习复杂映射多表操作。

• @Insert：实现新增

• @Update：实现更新

• @Delete：实现删除

• @Select：实现查询

• @Result：实现结果集封装

• @Results：可以与@Result一起使用，封装多个结果集

• @One：实现一对一结果集封装

• @Many：实现一对多结果集封装

6.2 MyBatis的增删改查

我们完成简单的user表的增删改查的操作:

6.2.1 添加UserMapper接口方法

//添加用户
   @Insert("insert into user values(#{id}, #{username}, #{password}, #{birthday})")
   public void addUser(User user);

   //更新用户
   @Update("update user set username = #{username} where id = #{id}")
   public void updateUser(User user);

   //查询用户
   @Select("select * from user")
   public List<User> selectUser();

   //删除用户
   @Delete("delete from user where id = #{id}")
   public void deleteUser(Integer id);

   //根据id查询用户
   @Select({"select * from user where id = #{id}"})
   public User findUserById(Integer id);

6.2.2 测试

private IUserMapper userMapper;
   private IOrderMapper orderMapper;

   @Before
   public void before() throws IOException {
       InputStream resourceAsStream = Resources.getResourceAsStream("sqlMapConfig.xml");
       SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(resourceAsStream);
       SqlSession sqlSession = sqlSessionFactory.openSession(true);
       userMapper = sqlSession.getMapper(IUserMapper.class);
       orderMapper = sqlSession.getMapper(IOrderMapper.class);
   }

   @Test
   public void addUser(){
       User user = new User();
       user.setId(3);
       user.setUsername("testName");
       user.setPassword("123");
       user.setBirthday(new Date());

       userMapper.addUser(user);
   }

   @Test
   public void updateUser(){
       User user = new User();
       user.setId(3);
       user.setUsername("updateTestName");

       userMapper.updateUser(user);

   }

   @Test
   public void selectUser(){
       List<User> users = userMapper.selectUser();
       for (User user : users) {
           System.out.println(user);
       }
   }

   @Test
   public void deleteUser(){
       userMapper.deleteUser(3);
   }

修改MyBatis的核⼼配置⽂件，我们使⽤了注解替代的映射⽂件，所以我们只需要加载使⽤了注解Mapper接⼝即可:

<mappers>
	<!--扫描使⽤注解的类-->
	<mapper class="com.lagou.mapper.UserMapper" </mapper>
</mappers>

或者指定扫描包含映射关系的接口所在的包也可以

<mappers>
	<!--扫描使⽤注解的类所在的包-->
	<package name="com.lagou.mapper"></package>
</mappers>

6.3 MyBatis的注解实现复杂映射开发

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，使用注解开发后，我们可以使用@Results注解，@Result注解，@One注解，@Many注解组合完成复杂关系的配置。

6.4 一对一查询

6.4.1 一对一查询的模型

用户表和订单表的关系为，一个用户有多个订单，一个订单只从属于一个用户

一对一查询的需求：查询一个订单，与此同时查询出该订单所属的用户

6.4.2 一对一查询的语句

对应的sql语句：

select * from orders;
select * from user where id=查询出订单的uid;

查询的结果如下：

6.4.3 创建Order和User实体

public class Order {
	private int id;
	private Date ordertime;
	private double total;
	//代表当前订单从属于哪⼀个客户
	private User user;
}


public class User {
	private int id;
	private String username;
	private String password;
	private Date birthday;
}

6.4.4 创建OrderMapper接口

public interface IOrderMapper {  
  
 //查询订单以及订单所属的用户信息  
 public List<Order> findOrderAndUser();  
  
}

6.4.5 使⽤注解配置Mapper

public interface IOrderMapper {

    //查询订单以及订单所属的用户信息
    @Results({
            @Result(property = "id", column = "id"),
            @Result(property = "orderTime", column = "ordertime"),
            @Result(property = "total", column = "total"),
            @Result(property = "user", column = "uid", javaType = User.class,
                    one = @One(select = "com.lemon.mapper.IUserMapper.findUserById")),
    })
    @Select("select * from orders")
    public List<Order> findOrderAndUser();
}

//根据id查询用户
   @Select({"select * from user where id = #{id}"})
   public User findUserById(Integer id);

6.4.6 测试结果

@Test
   public void oneToOne(){
       List<Order> orderAndUser = orderMapper.findOrderAndUser();
       for (Order order : orderAndUser) {
           System.out.println(order);
       }
   }

6.5 一对多查询

6.5.1 一对多查询的模型

用户表和订单表的关系为，一个用户有多个订单，一个订单只从属于一个用户

一对多查询的需求：查询一个用户，与此同时查询出该用户具有的订单

6.5.2 ⼀对多查询的语句

对应的sql语句：

select * from user;
select * from orders where uid=查询出⽤户的id;

查询的结果如下：

6.5.3 修改User实体

public class User {

    private int id;
    private String username;
    private String password;
    private Date birthday;
    //代表当前⽤户具备哪些订单
    private List<Order> orderList;
}

6.5.4 创建UserMapper接⼝

public interface IUserMapper {  
  
 //查询所有用户、同时查询每个用户关联的订单信息  
 public List<User> findAll();
}

6.5.5 使⽤注解配置Mapper

//查询所有用户、同时查询每个用户关联的订单信息
   @Results({
           @Result(property = "id", column = "id"),
           @Result(property = "username", column = "username"),
           @Result(property = "password", column = "password"),
           @Result(property = "birthday", column = "birthday"),
           @Result(property = "orderList", column = "id", javaType = List.class,
                   many = @Many(select = "com.lemon.mapper.IOrderMapper.findOrderByUid"))
   })
   @Select("select * from user")
   public List<User> findAll();

6.5.6 测试结果

@Test
   public void oneToMany(){
       List<User> all = userMapper.findAll();
       for (User user : all) {
           System.out.println(user);
       }
   }

6.6 多对多查询

6.6.1 多对多查询的模型

⽤户表和⻆⾊表的关系为，⼀个⽤户有多个⻆⾊，⼀个⻆⾊被多个⽤户使⽤

多对多查询的需求：查询⽤户同时查询出该⽤户的所有⻆⾊

6.6.2 多对多查询的语句

对应的sql语句：

select * from user;
select * from role r,user_role ur where r.id=ur.role_id and ur.user_id=⽤户的id

查询的结果如下：

6.6.3 创建Role实体，修改User实体

public class User {
	private int id;
	private String username;
	private String password;
	private Date birthday;
	//代表当前⽤户具备哪些订单
	private List<Order> orderList;
	//代表当前⽤户具备哪些⻆⾊
	private List<Role> roleList;
}


public class Role {
	private int id;
	private String rolename;
}

6.6.4 添加UserMapper接⼝⽅法

public List<User> findAllUserAndRole();

6.6.5 使⽤注解配置Mapper

//查询所有用户、同时查询每个用户关联的角色信息
   @Results({
           @Result(property = "id", column = "id"),
           @Result(property = "username", column = "username"),
           @Result(property = "password", column = "password"),
           @Result(property = "birthday", column = "birthday"),
           @Result(property = "roleList", column = "id", javaType = List.class,
                   many = @Many(select = "com.lemon.mapper.IRoleMapper.findRoleByUid"))
   })
   @Select("select * from user")
   public List<User> findAllUserAndRole();

6.6.6 测试结果

@Test
   public void ManyToMany(){
       List<User> all = userMapper.findAllUserAndRole();
       for (User user : all) {
           System.out.println(user);
       }
   }