MyBatis动态SQL特性详解

List<User> selectByCondition(User user);

<select id="selectByCondition" resultType="User">
    select *
    from user_table
    <!--需要使用where标签，否则两个条件为空时，会存在sql语法错误 -->
    <where>
        <if test="user != null and user != ''">
            user like #{user}
        </if>
        <if test="password != null and password != null">
            and password like #{password}
        </if>
    </where>
</select>

    /**
     * 动态条件查询：
     * 用户输入的可能不是全部参数，而是部分参数
     * 动态SQL
     */
    @Test
    public void ConditionSelectTest() throws IOException {
        //模拟前端传入参数
        String userName = "A";
        //String password = "4";
        //处理参数-配置为模糊查询形式
        userName = "%"+ userName + "%";
        //password = "%"+ password + "%";
        //封装成对象的形式传入
        User user = new User();
        user.setUser(userName);
        //user.setPassword(password);
        String resource = "mybatis-config.xml";
        InputStream is = Resources.getResourceAsStream(resource);
        SqlSessionFactory build = new SqlSessionFactoryBuilder().build(is);
        SqlSession sqlSession = build.openSession();
        UserMapper mapper = sqlSession.getMapper(UserMapper.class);
        //调用方法
        List<User> users = mapper.selectByCondition(user);
        users.forEach(System.out::println);
    }

//动态修改void alterRecordByName(User user);

<update id="alterRecordByName">
    update user_table
    <!--set标签 代表的就是set-->
    <set>
        <!--if标签 判断用户是否输入，不输入就不进行修改-->
        <if test="password != null and password != ''">
            password = #{password},
        </if>
        <if test="balance != null ">
            balance = #{balance}
        </if>
    </set>
    where user = #{user};
</update>

 /**
     * 修改部分-动态SQL
     */
    @Test
    public void testAlterCondition() throws IOException {
        //模拟前端传入参数
        String userName = "BB";
        //密码和账户余额修改任意，当前只修改账户余额
        //String password = "123456";
        int balance = 5000;
        //封装成对象的形式传入,只将账户余额进行对象封装，密码不变
        User user = new User();
        user.setUser(userName);
//        user.setPassword(password);
        user.setBalance(balance);
        String resource = "mybatis-config.xml";
        InputStream is = Resources.getResourceAsStream(resource);
        SqlSessionFactory build = new SqlSessionFactoryBuilder().build(is);
        //获取SqlSession对象的时候，openSession空参时:autoCommit = false
        SqlSession sqlSession = build.openSession();
        UserMapper mapper = sqlSession.getMapper(UserMapper.class);
        mapper.alterRecordByName(user);
        System.out.println("修改成功...");
        //需要手动提交，或者设置：openSession（true）
        sqlSession.commit();
    }

//参数为数组，可接收多个值
void deleteByBalances(@Param("balance") int[] balance);

<!--批量删除-->
<delete id="deleteByBalances">
    delete from user_table
    where balance in
    <foreach collection="balance" separator="," item="balance" open="(" close=")" >
        #{balance}
    </foreach>;
</delete>

 /**
 * 批量删除
 */
@Test
public void testDeletes() throws IOException {
    //模拟前端传入参数
    int[] balances = new int[]{2000,3000};
    String resource = "mybatis-config.xml";
    InputStream is = Resources.getResourceAsStream(resource);
    SqlSessionFactory build = new SqlSessionFactoryBuilder().build(is);
    //获取SqlSession对象的时候，openSession空参时:autoCommit = false(默认)
    SqlSession sqlSession = build.openSession();
    UserMapper mapper = sqlSession.getMapper(UserMapper.class);
    mapper.deleteByBalances(balances);
    System.out.println("删除成功---->");
    //需要手动提交，或者设置：openSession（true）
    sqlSession.commit();
}