MyBatis中的动态SQL（使用foreach）

Question

org.apache.ibatis.mapping.SqlMapperException: The expression 'list' evaluated to a null value.

我的java代码：

public  List<SearchVO> getSearchResultByParams(List<String> selectedGroups) {
    Map map = new HashMap(1);
    map.put("selectedGroups", selectedGroups);
    return MyMapper.getSearchResultByParams(map);
}

mymapper.xml：

<select id="getSearchResultByParams" parameterType="map" resultMap="SearchResultMap">
    SELECT *
    FROM WORK
    WHERE ID IN 
         <foreach item="selectedGroups" collection="list" open="(" separator="," close=")">
            #{selectedGroups}
        </foreach>
</select>

Answer 1

首先确保您在mybatis-config文件typeAliases标记中为java.util.HashMap设置了别名映射

<select id="getSearchResultByParams" parameterType="map" resultMap="SearchResultMap">
    SELECT *
    FROM WORK
    WHERE ID IN 
         <foreach collection="selectedGroups" item="item" index="index" open="(" separator="," close=")">
            #{item}
        </foreach>
</select>

集合必须是地图中列表的关键字

该文档可能会帮助您http://mybatis.github.io/mybatis-3/dynamic-sql.html