ibatis ,sqlmap文件中 iniclude标签的方法-优快云博客

本文链接：https://blog.youkuaiyun.com/sunrain_gao/article/details/593749

本文介绍了如何在iBATIS中使用<include>标签来重用SQL片段，以消除重复代码。通过创建<sql>标签定义可复用的SQL片段，并在需要的地方使用<include>标签进行引用，实现代码的简洁和维护性。注意<include>标签具备命名空间感知能力，可以跨SqlMap引用，但需确保被引用的片段在包含它的语句之前加载。

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http://opensource2.atlassian.com/confluence/oss/display/IBATIS/How+do+I+reuse+SQL-fragments

When writing SqlMaps, you often encounter duplicate fragments of SQL, for example a FROM-clause or constraint-statement; iBATIS offers a simple yet powerful tag to reuse them. For the sake of simplicity, let's assume we want to get some items and we want to do a count on them.

Normally, you would write something like this:

<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>

To eliminate this duplication, we use the tags <sql> and <include>. The <sql>-tag contains the fragment to reuse, the <include>-tag to include such a fragment:

<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>

The <include>-tag is namespace-aware so you can refer to fragments even when they are located in another map (however, due to the way iBATIS loads the SqlMaps, the included fragment should be loaded before the including statement).

The fragments are included and processed on query-execution so parameters can be used too:

<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>