mybatis批量update

更新單條記錄

UPDATE course SET name = 'course1' WHERE id = 'id1';

更新多條記錄的同一個字段為同一個值

UPDATE course SET name = 'course1' WHERE id in ('id1', 'id2', 'id3);

更新多條記錄為多個字段為不同的值

比較普通的寫法，是通過循環，依次執行update語句。

Mybatis寫法如下：

<update id="updateBatch"  parameterType="java.util.List">  
    <foreach collection="list" item="item" index="index" open="" close="" separator=";">
        update course
        <set>
            name=${item.name}
        </set>
        where id = ${item.id}
    </foreach>      
</update>

一條記錄update一次，性能比較差，容易造成阻塞。

PostgreSQL沒有提供直接的方法來實現批量更新，但可以使用case when語法來實現這個功能。

UPDATE course
    SET name = CASE id 
        WHEN 1 THEN 'name1'
        WHEN 2 THEN 'name2'
        WHEN 3 THEN 'name3'
    END, 
    title = CASE id 
        WHEN 1 THEN 'New Title 1'
        WHEN 2 THEN 'New Title 2'
        WHEN 3 THEN 'New Title 3'
    END
WHERE id IN (1,2,3)

這條sql的意思是，如果id為1，則name的值為name1，title的值為New Title1；依此類推。

在Mybatis中的配置則如下：

<update id="updateBatch" parameterType="list">
        update course
          <trim prefix="set" suffixOverrides=",">
             <trim prefix="peopleId =case" suffix="end,">
                 <foreach collection="list" item="i" index="index">
                         <if test="i.peopleId!=null">
                          when id=#{i.id} then #{i.peopleId}
                         </if>
                 </foreach>
             </trim>
             <trim prefix=" roadgridid =case" suffix="end,">
                 <foreach collection="list" item="i" index="index">
                         <if test="i.roadgridid!=null">
                          when id=#{i.id} then #{i.roadgridid}
                         </if>
                 </foreach>
             </trim>     
            
             <trim prefix="type =case" suffix="end," >
                 <foreach collection="list" item="i" index="index">
                         <if test="i.type!=null">
                          when id=#{i.id} then #{i.type}
                         </if>
                 </foreach>
             </trim>
            
       		<trim prefix="unitsid =case" suffix="end," >
                  <foreach collection="list" item="i" index="index">
                          <if test="i.unitsid!=null">
                           when id=#{i.id} then #{i.unitsid}
                          </if>
                  </foreach>
        	</trim>
      	</trim>
            where
            <foreach collection="list" separator="or" item="i" index="index" >
              id=#{i.id}
          </foreach>
</update>

<update id="updateUserLog" parameterType="java.util.List">
    update ps_user_log
    SET dept_id =
    <foreach collection="list" item="item" index="index"
             separator=" " open="case id" close="end">
        when #{item.id} then #{item.deptId}
    </foreach>
    , type =
    <foreach collection="list" item="item" index="index"
             separator=" " open="case id" close="end">
        when #{item.id} then #{item.type}
    </foreach>
    where id in (
    <foreach collection="list" item="item" index="index"
             separator=",">
        #{item.id}
    </foreach>
    )
</update>