重用动态SQL片段 [英] Reusing dynamic sql fragments

问题描述

在那儿，我正在开发Primefaces应用，作为持久层，我选择了 Mybatis .

Hei there, I'm working on a Primefaces app and as a persistence layer I chose Mybatis.

这是常规sql在我的映射器中的外观:

This is how a regular sql would look in my mapper:

<select id="getAllTransportUnit" resultMap="TransportUnitMap">
    SELECT * FROM SSLS_GUI.VW_TU
    <if test="( hasFilters == 'yes' ) and ( parameters != null )">
        <where>
            <foreach item="clause" collection="parameters" separator=" AND "
                open="(" close=")">
                UPPER(${clause.column}) ${clause.operator} #{clause.value}
            </foreach>
        </where>
    </if>
    <if test="sort == 'true'">
        ORDER BY ${sortField}
        <if test="sortOrder == 'DESC'"> DESC</if>
        <if test="sortOder == 'ASC'"> ASC</if>
    </if>
</select>

几乎所有我的查询都使用从<if test...>开始的动态sql部分.是否可以将其放在单独的文件中，然后在我的所有查询中重复使用?

Almost all my queries use the dynamic sql part starting from the <if test...>. Is it possible to put it in a separate file and then reuse it all over my queries?

推荐答案

有几种方法可以重用sql代码段.

There are several options how to reuse sql snippets.

第一个正在使用include.创建单独的映射器Common.xml:

The first one is using include. Create separate mapper Common.xml:

<mapper namespace="com.company.project.common">
    <sql id="orderBy>
      <if test="sort == 'true'">
        ORDER BY ${sortField}
        <if test="sortOrder == 'DESC'"> DESC</if>
        <if test="sortOder == 'ASC'"> ASC</if>
      </if>
    </sql>


    <sql id="filters">
     <if test="( hasFilters == 'yes' ) and ( parameters != null )">
      <where>
        <foreach item="clause" collection="parameters" separator=" AND "
            open="(" close=")">
            UPPER(${clause.column}) ${clause.operator} #{clause.value}
        </foreach>
     </where>
    </if>
  </sql>
</mapper>

并在其他映射器MyMapper.xml中使用它:

And the use it in other mappers MyMapper.xml:

<select id="getAllTransportUnit" resultMap="TransportUnitMap">
  SELECT * FROM SSLS_GUI.VW_TU
  <include refid="com.company.project.common.filters"/>
  <include refid="com.company.project.common.orderBy"/>
</select>

为避免每个副本中的名称空间重复，您可以在MyMapper.xml中创建快捷方式片段:

To avoid duplicating namespace in every include you can create shortcut snippets in MyMapper.xml:

<sql id="orderBy">
  <include refid="com.company.project.common.orderBy"/> 
</sql>

<select id="getAllTransportUnit" resultMap="TransportUnitMap">
  SELECT * FROM SSLS_GUI.VW_TU
  <include refid="orderBy"/>
</select>

Mybatis速度宏

另一个可能的选择是使用mybatis 脚本.使用mybatis-velocity脚本引擎，您可以定义速度宏并像这样重用它.

Mybatis-velocity macro

Another possible option is to use mybatis scripting. Using mybatis-velocity scripting engine you can define velocity macro and reusing it like this.

在Commons.xml中:

<sql id="macros"
  #macro(filters)
    #if ( $_parameter.hasFilters )
      #repeat( $_parameter.parameters $clause "AND" " (" ")" )
        ${clause.column} ${clause.operator} @{clause.value}
      #end
    #end
  #end

  #macro(order_by)
  .. 
  #end
</sql>

在MyMapper.xml中:

<select id="getAllTransportUnit" resultMap="TransportUnitMap">
  <include refid="macros"/>
  SELECT * FROM SSLS_GUI.VW_TU
  #filters()
  #order_by()
</select>

通过sql片段包含宏不是重用宏的最干净方法.只是一个想法，如何使用.

Including macros via sql snippet is not the most clean way to reuse macros. It is just an idea how this is used.

更好的选择是配置mybatis-velocity并指定可用的全局宏.在这种情况下，无需包含macros代码段，结果查询将如下所示:

Much better option is to configure mybatis-velocity and specify what global macros are available. In this case there will be no need to do include of macros snippet and result query will be like this:

<select id="getAllTransportUnit" resultMap="TransportUnitMap">
  SELECT * FROM SSLS_GUI.VW_TU
  #filters()
  #order_by()
</select>

这篇关于重用动态SQL片段的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！