查询条件下拉框联动，如果一级为空，二级也为空

 直接祭出代码

template中
              <el-col  :xs="24" :sm="12" :md="8" :lg="6">
                <el-form-item label="楼宇">
                  <el-select v-model="searchData.buildingId" clearable  @change="getUnitListByBuildSearch">
                    <el-option v-for="item in buildings" :key="item.code" :label="item.value" :value="item.code"></el-option>
                  </el-select>
                </el-form-item>
              </el-col>
              <el-col  :xs="24" :sm="12" :md="8" :lg="6">
                <el-form-item label="单元号">
                  <el-select v-model="searchData.unitId" clearable  @change="changeData">
                    <el-option v-for="item in units" :key="item.code" :label="item.value" :value="item.code"></el-option>
                  </el-select>
                </el-form-item>
              </el-col>

data中
      buildings: [], // 获取楼宇
      units: [] // 获取单元
methods中
// 根据楼宇获取单元
getUnitListByBuildSearch () {
    if (this.searchData.buildingId === '') {
        this.searchData.unitId = ''
        this.units = []
        return false
     }
     this.searchData.unitId = ''
     this.$http.post(apis.GetMstUnit, {id: this.searchData.buildingId}).then(res => {
         if (res.data.code === 200) {
             this.units = res.data.data.record
         }
     })
},