iBATIS如何复用SQL片段(转载)

当我们写SqlMaps的时候,经常会碰到重复的SQL片段,例如From语句或者约束条件;iBATIS提供了一个强大的标签来复用这些重复片段,简单举例,我们想检索一些字段,并且想统计它们。

通常情况下,你会这样写:

<select id="selectItemCount" resultClass="int">      
 SELECT COUNT(*) AS total       
  FROM items       
  WHERE parentid = 6      
<select>      
<select id="selectItems" resultClass="Item">      
  SELECT id, name       
  FROM items       
  WHERE parentid = 6      
<select>      

为了消除重复片段,我们使用【sql】和【include】标签。【sql】标签用来包含重复片段,【include】标签用来引入片段:

<sql id="selectItem_fragment">      
  FROM items       
  WHERE parentid = 6      
<sql>      
<select id="selectItemCount" resultClass="int">      
  SELECT COUNT(*) AS total       
  <include refid="selectItem_fragment"/>      
<select>      
<select id="selectItems" resultClass="Item">      
  SELECT id, name       
  <include refid="selectItem_fragment"/>      
<select>      

【inclued】标签是一个命名空间可知的,所以你可以引入其他map的片段.(但是,因为iBATIS引入SqlMap的顺序,被引入的片段,要优先于欲引入的sql部分被导入)

重复片段在查询执行时被引入和执行,所以参数依然可以使用:

<sql id="selectItem_fragment">      
  FROM items       
  WHERE parentid = #value#       
<sql>      
<select id="selectItemCount" parameterClass="int" resultClass="int">      
  SELECT COUNT(*) AS total       
  <include refid="selectItem_fragment"/>      
<select>
<select id="selectItems" parameterClass="int" resultClass="Item">      
  SELECT id, name       
  <include refid="selectItem_fragment"/>      
<select>

转自:http://sinokaka.iteye.com/blog/39274

posted @ 2013-01-09 23:19  horizon~~~  阅读(671)  评论(0编辑  收藏  举报