MyBatis的SQL语句标签用法

• foreach
  输入的列表、数组、map转化为SQL语句中的用括号括起来的字符串
  例子：
  Mapper接口定义的方法：UserList为模拟返回的数据对象

List<UserList> getUserInfo(@Param("userName") List<String> userName);

Mapper.xml动态sql构建，下面foreach标签内的值可以将数组转化为类似(1,2,3)的字符串

 <select id="getUserInfo" resultType="com.test.UserList">
          SELECT
            *
          FROM user_info
            where
            <if test="userName!= null and userName.size() >0">
                USERNAME IN
                <foreach collection="userName" item="value" separator="," open="(" close=")">
                    #{value}
                </foreach>
            </if>
</select>

下面SQL转化的例子

SELECT * FROM user_info WHERE (USERNAME,AGE) IN (('张三','26'),('李四','58'),('王五','27'),......);

实际的foreach标签

 <select id="getUserInfo" resultType="com.test.UserList">
            SELECT
                *
            FROM user_info
            where
            <if test="user!= null and user.size() >0">
                (USERNAME,AGE) IN
                <foreach collection="user.entrySet()" item="value" index="key" separator="," open="(" close=")">
                    (#{key},#{value})
                </foreach>
            </if>
</select>