详解mybatis中的if-else的嵌套使用

2022-11-13 12:11:03 mybatis 详解

案例一：if-else

在mybatis的使用过程中，难免会存在使用if-else的逻辑，但是实际是没有这种语法的，提供了choose标签来替代这种语法

   <select id="selectUserByState" resultType="com.bz.model.entity.User">
    SELECT
      *
    FROM
      user
    WHERE
      1=1
    <choose>
      <when test="state == 1">
        AND name = #{name1}
      </when>
     <when test="state == 2">
        AND name = #{name2}
      </when>
      <otherwise>
        AND name = #{name3}
      </otherwise>
    </choose>
  </select>

案例二：if嵌套

在实际的编码过程中会对一些条件进行重复判断，并对内深入if判断，这时就可以使用if嵌套

  <select id="selectUserByState" resultType="com.bz.model.entity.User">
    SELECT
      *
    FROM
      user
    WHERE
     <if test=" gender!=null and gender!='' "> 
         <if test=" gender==male ">
             and name=#{name}
         </if>
     </if>
  </select>

MyBatis中if和choose的嵌套

    <!-- public List<VadtaxShow> findList(VadtaxShow vadtaxShow); -->
    <select id="findList" parameterType="com.cdqyzj_WC.Backstage.vaddedtax.domain.VaddeTax" resultType="com.cdqyzj_WC.Backstage.vaddedtax.domain.VaddeTax">
    SELECT t.addedId,t.taxType,t.totalSales,t.outputTax,t.inputTax,t.entryAmount, t.amountTax,t.retentionTax,
    t.createTime, t.taxTime,t.comId,c.comName,c.comType
    FROM t_g_vaddedtax AS t JOIN t_ucompany AS c ON c.comId = t.comId
    <where>
    1=1
            <if test="comType != '' and comType != null"> and c.comType = #{comType}</if>
            <if test="taxTime != null and taxTime != ''"> and t.taxTime =#{taxTime} </if>    
            <if test="taxType != null and taxType != '' "> and t.taxType =#{taxType} </if>
            <if test="comId != null and comId != '' and comId != 0 "> and t.comId =#{comId} </if>    
            <if test="start_times != null and end_times != null">
                <choose>
                    <when test="middle_times != null">
                        and t.createTime in ('${start_times}','${middle_times}', '${end_times}' )
                    </when>
                    <otherwise>
                        and t.createTime in ('${start_times}','${end_times}' )
                    </otherwise>
                </choose>
            </if>
            <if test="orderBy != null and orderType != '' ">
                     order by ${orderBy}  ${orderType}
            </if>
            <if test="pageSize != 0 ">
                    limit ${startRows},${pageSize}
            </if>
    </where>
    </select>

功能实现之后反思：要不我不对“middle_times”判空？这样不就不用嵌套了吗？

    <!-- public List<VadtaxShow> findList(VadtaxShow vadtaxShow); -->
    <select id="findList" parameterType="com.cdqyzj_WC.Backstage.vaddedtax.domain.VaddeTax" resultType="com.cdqyzj_WC.Backstage.vaddedtax.domain.VaddeTax">
    SELECT t.addedId,t.taxType,t.totalSales,t.outputTax,t.inputTax,t.entryAmount, t.amountTax,t.retentionTax,
    t.createTime, t.taxTime,t.comId,c.comName,c.comType
    FROM t_g_vaddedtax AS t JOIN t_ucompany AS c ON c.comId = t.comId
    <where>
    1=1
            <if test="comType != '' and comType != null"> and c.comType = #{comType}</if>
            <if test="taxTime != null and taxTime != ''"> and t.taxTime =#{taxTime} </if>    
            <if test="taxType != null and taxType != '' "> and t.taxType =#{taxType} </if>
            <if test="comId != null and comId != '' and comId != 0 "> and t.comId =#{comId} </if>    
            <if test="start_times != null and end_times != null">
                and t.createTime in ('${start_times}','${middle_times}', '${end_times}' )
            </if>
            <if test="orderBy != null and orderType != '' ">
                     order by ${orderBy}  ${orderType}
            </if>
            <if test="pageSize != 0 ">
                    limit ${startRows},${pageSize}
            </if>
    </where>
    </select>

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