关于mybatis返回map集合的操作:
1.mapper.xml中写一个查询返回map的sql
<select id="findMap" parameterType="com.sxd.swapping.domain.HuaYangArea" resultType="java.util.HashMap">
select
hy.uid,
hy.area_name
from
hua_yang_area AS hy
<where>
<if test="areaPerson != null">
AND hy.area_person >= #{areaPerson}
</if>
</where>
</select>
2.mapper.java 对应接收,注意,这里并不是直接使用Map<>接收,因为sql查出的不是一条数据,而是多条数据,所以是List<Map<>>接收
/**
* mybatis 查询接收map集合
* @param area
* @return
*/
List<Map<String,String>> findMap(HuaYangArea area);
3.错误写法:
错误的写法就是直接读取List中的Map<>
@Override
public Map<String, String> findMap(HuaYangArea entity) {
List<Map<String,String>> list = huaYangAreaMapper.findMap(entity);
Map<String,String> res = new HashMap<>();
for (Map<String, String> stringStringMap : list) {
System.out.println(stringStringMap.toString());
stringStringMap.forEach((k,v)->{
System.out.println("key:"+k+">>>value:"+v);
res.put(k,v);
});
}
return res;
}
这样查询到的结果是:
我们需要看一哈实际List<Map<>>中到底存储的是什么
结果集中存储是按照{字段名1:字段值1,字段名2:字段值2}
而我们其实期望的是{字段值1:字段值2}
4.正确写法:
所以正确的写法应该是
@Override
public Map<String, String> findMap(HuaYangArea entity) {
List<Map<String,String>> list = huaYangAreaMapper.findMap(entity);
Map<String,String> res = new HashMap<>();
for (Map<String, String> stringStringMap : list) {
System.out.println(stringStringMap.toString()); String uid = null;
String areaName = null; for (Map.Entry<String,String> entry:stringStringMap.entrySet()){
if ("uid".equals(entry.getKey())){
uid = entry.getValue();
}else {
areaName = entry.getValue();
}
} res.put(uid,areaName);
}
return res;
}
返回结果: