Spring Mybatis 动态语句 总结

1.简介

Mybatis 提供动态语句的功能来增强多条件变动的查询语句。

2.代码

if和where搭配使用：

<select id="query" resultType="a">
    select * from t_a
    <where><!--  where内没有条件满足，不转成where，有条件满足转成where。自动去掉多余的and和or -->
	    <if test="name != null">
	    a_name = #{name}
	    </if>
	    <if test="price != null and price &gt; 100">
	    <!--  &gt;是 >  &lt;是 < -->
	    and a_prirce = #{price}
	    </if>
    </where>
</select>

set标签用于去掉多余逗号，和自动添加set关键字：

<!--    set标签用于去掉多余逗号，和自动添加set关键字-->
<update id="update">
    update t_a
    <set>
        <if test="aName != null">
             a_name = #{aName},
        </if>
        <if test="aPrice != null">
             a_price = #{aPrice}
        </if>
        where a_id = #{aId}
    </set>
</update>

trim可以自定义添加关键字，去掉指定字符:

<select id="queryTrim" resultType="a">
    select * from t_a
    <!--  自动添加where，去掉多余前缀的and和or -->
    <trim prefix="where" prefixOverrides="and|or" sufixOverrides="and|or">
	    <if test="name != null">
	    a_name = #{name}
	    </if>
	    <if test="price != null and price &gt; 100">
	    <!--  &gt;是 >  &lt;是 < -->
	    and a_prirce = #{price}
	    </if>
    </trim>
</select>

<select id="queryTrim" resultType="a">
    select * from t_a
    <!--  自动添加where，去掉多余后缀的and和or -->
    <trim prefix="where" sufixOverrides="and|or">
	    <if test="name != null">
	    a_name = #{name} and
	    </if>
	    <if test="price != null and price &gt; 100">
	    <!--  &gt;是 >  &lt;是 < -->
	    a_prirce = #{price}
	    </if>
    </trim>
</select>

choose搭配when使用实现类似switch的功能：

<select id="queryChoose" resultType="a">
    select * from t_emp
   where
    <!-- 如果name !=null 则用name查询，如果name == null 则用price查询,如果都不满足，则走otherwise分支 -->
    <choose>
        <when test="name != null">
            a_name = #{name} and
        </when>
        <when test="salary != null">
            a_price = #{salary}
        </when>
        <otherwise>1=1</otherwise>
    </choose>
</select>

foreach实现批量查询：

<select id="queryBatch" resultType="a">
    select * from t_a
     where a_id in
     <!-- 实现(id1,id2,id3...idn)--> 
     <foreach collection="ids" open="(" separator="," close=")" item="id">
         #{id}
     </foreach>     
</select>

<sql id="mySql">
    select * from t_a
</sql>
<select id="query" resultType="a">
    <include refid="mySql"/>
</select>