MyBatis if判断无效果 新手求帮助！

[l371890934]

新手一枚，刚参加社会培训，远程视频教学，很多功能及代码实现都是自已想的，代码不规范请谅解！
进入正题：
欲实现一个根据select下拉列表中的value值进行排序，当select无选中时整个表进行排序。现在问题是依据下拉列表进行排序正常，select无选中项再点击排序无效果
代码如下：
DAO代码：
//依据传入的order(列名) 自定义类Cost进行排序
public List<Cost> orderDesc(@Param("order") String order,@Param("cost")Cost cost);
XML文件：
<select id="orderDesc" resultType="com.entity.Cost">
select cost_id as costId,name,base_duration as baseDuration,base_cost as baseCost,
unit_cost as unitCost,status,descr,creatime,startime,cost_type as costType
from cost
<choose>
<when test="#{cost.costType}!=null">
where cost_type=#{cost.costType} order by ${order} desc
</when>
<otherwise>
order by ${order} desc
</otherwise>
</choose>
</select>
想要的效果是当 cost.costType为null时 直接order By 列名 排序
两次代码执行时log4j的输出是这样的：
select选中时：
DEBUG - ==> Preparing: select cost_id as costId,name,base_duration as baseDuration,base_cost as baseCost, unit_cost as unitCost,status,descr,creatime,startime,cost_type as costType from cost where cost_type=? order by baseCost desc
DEBUG - ==> Parameters: 1(String)
select无选中时:
DEBUG - ==> Preparing: select cost_id as costId, name, base_duration as baseDuration, base_cost as baseCost, unit_cost as unitCost, status, descr, creatime, startime, cost_type as costType from cost where cost_type=? order by baseCost asc
DEBUG - ==> Parameters: null(String)
DEBUG - <== Total: 0

求大神解答！！

[执笔记忆的空白]

恩，楼上正解，标签里面不用#{} 直接写属性名称判断就行了

[打不打伞心都是湿]

if在哪………………？

[小雷同学]

还有 似乎可以直接写costType 不用写cost.costType的吧？

[火阳邪神]

XML中判断不用#{} ，sql中不用cost.costType，直接costType

[suciver]

<when test="#{cost.costType}!=null">不要用#{}在标签中直接用<when test="cost.costType!=null"> #{}是用在sql中的标签中不用