vue2 elementui if导致的rules判断失效

优化目标 和 目标转化出价必填的 切换的时候还会隐藏掉 这时候的if语句会导致rules判断失效

我的办法是把判断拉到外面 别放在el-form-item里

<section v-if="unitForm.baseTarget === 'OCPM' && unitForm.cpaTargetOptions !== undefined && unitForm.cpaTargetOptions.length > 0">
  <el-form-item prop="cpaTarget" label="优化目标" required>
    <el-select 
      style="width: 300px;"
      v-model="unitForm.cpaTarget" 
      placeholder="请选择优化目标"
      clearable
      @change="(value)=>changeCpaTarget(value)"
      >
      <el-option
        v-for="item in unitForm.cpaTargetOptions"
        :key="item.value"
        :label="item.label"
        :value="item.value">
      </el-option>
    </el-select>
  </el-form-item>
</section>
rules: { 
  cpaTarget: [
    { required: true, message: '请选择优化目标', trigger: 'change' }
  ], 
}