mybatis中傳入String類型參數異常

在使用mybatis時，寫了一條sql語句，只有一個String類型的參數， 示例代碼

<select id="getApplyNum" parameterType="java.lang.String" resultType="java.util.Map">
         SELECT
            t.activity_id AS "activityId",
            COUNT(1) AS "count"
        FROM
            t_user t
        WHERE
            t.activity_id IN (${ids})
        GROUP BY
            t.activity_id
    </select>

Mybatis查詢sql傳入一個字符串傳參數，報There is no getter for property named 'ids' in 'class java.lang.String'。

後來改成如下寫法，無論參數名是啥，都要改成"_parameter"。問題解決。

 <select id="getApplyNum" parameterType="java.lang.String" resultType="java.util.Map">
         SELECT
            t.activity_id AS "activityId",
            COUNT(1) AS "count"
        FROM
            t_user t
        WHERE
            t.activity_id IN (${_parameter})
        GROUP BY
            t.activity_id
    </select>