5. Mybatis注解开发

常用注解

• @Insert ：实现新增
• @Update：修改
• @Delete：删除
• @Select：查询
• @Result：结果集封装
• @Results：跟result一起用，封装多个结果集
• @One：一对一结果集封装

• @Many：一对多结果集封装

  增删改查

   // 增加用户
    @Insert("insert into user values (#{id},#{name})")
    void insertUser(User user);
    // 更新用户
    @Update("update user set name = #{name} where id = #{id}")
    void updateUser(User user);
    // 查询
    @Select("select * from user")
    List<User> selectUser();
    // 删除
    @Delete("delete from user where id = #{id}")
    void deleteUser(Integer id);

  一对一查询

  ```java @Results({ @Result(property = “orderId”,column = “order_id”), @Result(property = “name”,column = “name”), @Result(property = “user”,column = “user_id”,javaType = User.class,

        one = @One(select = "com.lagou.entity.dao.UserDao.findUserById"))

  }) @Select(“select * from order“) List findOrderAndUser2();

@Select(“select * from user where id = #{id}”) User findUserById(Integer id);

<a name="tBhBy"></a>
## 一对多查询
```java
// 先查询order，返回的user_id字段用来当入参传给findUsers,再查询的结果返回封装
@Results({
    @Result(property = "orderId",column = "order_id"),
    @Result(property = "name",column = "name"),
    @Result(property = "user",column = "user_id",javaType = List.class,
            many = @Many(select = "com.lagou.entity.dao.UserDao.findUsers"))
})
@Select("select * from `order`")
List<Order> findOrderAndUser2();
@Select("select * from user where id = #{id}")
List<User> findUsers(Integer id);

多对多查询

@Select("select * from user")
@Result({
    @Result(property = "id",column = "id")
    @Result(property = "name",column = "name")
    @Result(property = "roleList",column = "id",javaType = List.class,
           many = @Many(select = "com.lagou.entity.dao.RolerDao.findRoleByUid"))
})
List<User> findAllUserAndRole();
@Select("select * from role r,user_role ur where r.rid = ur.rid and ur.uid = #{uid}")
List<Role> findRoleByUid(Integer uid);