Mybatis增删改查基础

MyBatis可根据查询的结果类型、查询条件的不同进行统一处理。

1 查询数据

1.1 根据查询数据条数来分析不同的情况

1.1.1 查询单条数据

可以通过实体类、list集合、map等处理查询结果。

• 通过实体类查询单条数据

   User queryUserById(@Param("id") Integer id);

   <select id="queryUserById" resultType="User">
       select * from t_user where id = #{id}
   </select>

• 通过map接收

 Map<String, Object> queryUserMapById(@Param("id") Integer id);

 <select id="queryUserMapById" resultType="map">
     select * from t_user where id = #{id}
 </select>

1.1.2 查询多条数据

• 通过类型为Map的list集合接收

    List<Map<String, Object>> queryUserMapList();

    <select id="queryUserMapList" resultType="map">
      select * from t_user
    </select>

• 通过类型为实体的list集合接收

    List<User> selectUserList();

    <select id="selectUserList" resultType="User">
      select * from t_user
    </select>

• 通过map接收

一条数据对应一个map，此时需要通过@MapKey注解设置map集合的键，值是每条数据对应的map集合

注意：此时一定不能使用实体类对象接收，会抛出TooManyResultsException

    @MapKey("id")
    Map<String, Object> getAllUserToMap();

    <select id="getAllUserToMap" resultType="map">
    	select * from t_user
    </select>

1.2 其他情形

1.2.1 模糊查询

    List<User> queryUserByLike(@Param("username") String username);

    <select id="queryUserByLike" resultType="User">
      <!-- select * from t_user where username like '%${username}%' -->
      <!-- select * from t_user where username like concat('%', #{username}, '%') -->
      select * from t_user where username like "%"#{username}"%"
    </select>

1.2.2 动态表名

    List<User> queryAllUser(@Param("tableName") String tableName);

    <select id="queryAllUser" resultType="User">
      select * from ${tableName}
    </select>

2 新增数据

2.1 通过实体类新增

    @Test
    public void testInsertUser(){
      SqlSession sqlSession = SqlSessionUtil.getSqlSession();
      UserMapper userMapper = sqlSession.getMapper(UserMapper.class);
      User user = new User();
      user.setUsername("中华");
      user.setPassword("123456");
      user.setAge(32);
      user.setSex("男");
      int i = userMapper.insertUser(user);
      System.out.println(i);
    }

    int insertUser(User user);

    <insert id="insertUser">
      insert into t_user values(null, #{username}, #{password}, #{age}, #{sex})
    </insert>

此处，表的主键设计为自增。

也可以明确设置主键为自增：

    <!--
       useGeneratedKeys:设置使用自增主键
       keyProperty:自增主键放在传所参数对象的字段属性名，会将生成的自增主键设置到入参的字段中
       keyColumn:自增主键对应表的字段名
    -->
    <insert id="insertUser" useGeneratedKeys="true" keyProperty="id" keyColumn="id" parameterType="User">
      insert into t_user values(null, #{username}, #{password}, #{age}, #{sex})
    </insert>

2.2 通过map新增

    @Test
    public void testQueryByMapParam(){
      SqlSession sqlSession = SqlSessionUtil.getSqlSession();
      UserMapper userMapper = sqlSession.getMapper(UserMapper.class);
      Map<String, Object> map = new HashMap<>();
      map.put("username", "李斯");
      map.put("age", 23);
      map.put("password", "000000");
      map.put("sex", "女");
      List<User> admin = userMapper.insertUser(map);
      admin.stream().forEach(System.out::println);
    }

    int insertUser(Map<String, Object> map);

    <insert id="insertUser" useGeneratedKeys="true" keyProperty="id" keyColumn="id" parameterType="map">
      insert into t_user values(null, #{username}, #{password}, #{age}, #{sex})
    </insert>

3 修改数据

    int udpateUserById(User user);

    <update id="udpateUserById" parameterType="User">
      update t_user set username = #{username}, password = #{password} where id = #{id}
    </update>

4 删除数据

4.1 单个删除

    int deleteUserById(@Param("id") String id);

    <delete id="deleteUserById">
      delete from t_user where id = #{id}
    </delete>

4.2 批量删除

    int deleteUserByIds(@Param("ids") String ids);

    <delete id="deleteUserByIds">
      delete from t_user where id in (${ids})
    </delete>

    int result = deleteMapper.deleteUserByIds("5,6,7");