这种数据结构，点击扩展按钮获取此项的包含的列表数据信息。

<el-table
  ref="multipleTable"
  :data="chooseData"
  tooltip-effect="dark"
  style="width: 100%"
  :row-key="(row) => row.id"
  @expand-change="handleExpandChange"
  border
>

<el-table-column type="expand">
  <template #default="props">
    <div class="pl-12 pr-12">
      <el-table :ref="`item${props.row.id}`" :data="props.row.itemData" size="small" border row-key="id"
                @selection-change="handleSelectionChange(props.row,$event)">
        <el-table-column
          type="selection"
          :reserve-selection="true"
          width="55">
        </el-table-column>
        <el-table-column
          show-overflow-tooltip
          label="库存编号"
          prop="tagNum">
        </el-table-column>
        <el-table-column
          show-overflow-tooltip
          label="库位"
          prop="locationName">
        </el-table-column>
        <el-table-column
          show-overflow-tooltip
          label="现存容量"
          prop="capacity">
          <template slot-scope="scope">
      {{ scope.row.capacity }}{{ scope.row.skuCapacityUnitName }}
    </template>
        </el-table-column>
      </el-table>
      <div class="display-flex fd-row-reverse mt-20">
        <!-- 表格数据的分页的功能 -->
        <el-pagination
          hide-on-single-page
          @current-change="changePage(props.row,$event)"
          :current-page="props.row.pageNum"
          :page-size="props.row.pageSize"
          background
          layout="total, prev, pager, next, jumper"
          :total="props.row.itemTotal">
        </el-pagination>
      </div>
    </div>
  </template>
</el-table-column>
<el-table-column show-overflow-tooltip prop="chemicalName align="center label="化          学品名称">
</el-table-column>
....
</el-table>

方法：

选中的项自动展开，点击新增按钮打开dialog并进行选中项的展开和选中回显。

add () {
   //tableData选中项集合
   //chooseData可选的列表数据
  this.bakTableData = JSON.parse(JSON.stringify(this.tableData))
  this.chooseData.forEach(item => {
    item.multipleSelection = this.bakTableData.filter(i => i.id === item.id).length ? this.bakTableData.filter(i => i.id === item.id)[0].multipleSelection : []
    item.multipleSelectionBak = this.bakTableData.filter(i => i.id === item.id).length ? this.bakTableData.filter(i => i.id === item.id)[0].multipleSelectionBak : []
  })
  this.chooseDialog = true
  this.$nextTick(() => {
    this.chooseData.forEach(item => {
      if (this.bakTableData.filter(i => i.id === item.id).length) {
        this.$refs.multipleTable.toggleRowExpansion(item, true)
        //toggleRowExpansion展开扩展按钮，展开后会调用handleExpandChange方法
      }
    })
  })
},

handleExpandChange (row, expandedRows) {
  // 备份一下选中数据
  row.multipleSelectionBak = JSON.parse(JSON.stringify(row.multipleSelection))
  // 判断是打开还是收起
  const index = expandedRows.findIndex(item => item.id === row.id)
  if (index !== -1) {
    // 打开
    row.pageNum = 1
    this.getItemData(row)
  }
},

getItemData (row) {
  this.$api.storage.itemList({ hxpSkuId: row.id, pageNum: row.pageNum, pageSize:            row.pageSize }).then(res => {
    row.itemData = res.list
    row.itemTotal = res.total
    this.$nextTick(() => {
      const ids = row.multipleSelectionBak.map(i => i.id)
      row.itemData.forEach(item => {
        if (ids.includes(item.id)) {
          this.$refs[`item${row.id}`].toggleRowSelection(item, true)
        }
      })
    })
  })
},

//页码变化时候调用

changePage (row, val) {
  row.pageNum = val
  this.getItemData(row)
},