ElementUI table标签如何让某一行默认展开

<template lang="html">
    <el-table
        :data="tableData5"
        :row-key="getRowKeys"
        :expand-row-keys="expands"
        style=" 100%">
        <el-table-column type="expand">
            <template scope="props">
                <el-form label-position="left" inline class="demo-table-expand">
                    <el-form-item label="商品名称">
                        <span>{{ props.row.name }}</span>
                    </el-form-item>
                    <el-form-item label="所属店铺">
                        <span>{{ props.row.shop }}</span>
                    </el-form-item>
                    <el-form-item label="商品 ID">
                        <span>{{ props.row.id }}</span>
                    </el-form-item>
                    <el-form-item label="店铺 ID">
                        <span>{{ props.row.shopId }}</span>
                    </el-form-item>
                    <el-form-item label="商品分类">
                        <span>{{ props.row.category }}</span>
                    </el-form-item>
                    <el-form-item label="店铺地址">
                        <span>{{ props.row.address }}</span>
                    </el-form-item>
                    <el-form-item label="商品描述">
                        <span>{{ props.row.desc }}</span>
                    </el-form-item>
                </el-form>
            </template>
        </el-table-column>
        <el-table-column
            label="商品 ID"
            prop="id">
        </el-table-column>
        <el-table-column
            label="商品名称"
            prop="name">
        </el-table-column>
        <el-table-column
            label="描述"
            prop="desc">
        </el-table-column>
    </el-table>
</template>

<script>
export default {
    data() {
        return {
            tableData5: [{
                id: '12987122',
                name: '好滋好味鸡蛋仔',
                category: '江浙小吃、小吃零食',
                desc: '荷兰优质淡奶，奶香浓而不腻',
                address: '上海市普陀区真北路',
                shop: '王小虎夫妻店',
                shopId: '10333'
            }, {
                id: '12987123',
                name: '好滋好味鸡蛋仔',
                category: '江浙小吃、小吃零食',
                desc: '荷兰优质淡奶，奶香浓而不腻',
                address: '上海市普陀区真北路',
                shop: '王小虎夫妻店',
                shopId: '10333'
            }, {
                id: '12987125',
                name: '好滋好味鸡蛋仔',
                category: '江浙小吃、小吃零食',
                desc: '荷兰优质淡奶，奶香浓而不腻',
                address: '上海市普陀区真北路',
                shop: '王小虎夫妻店',
                shopId: '10333'
            }, {
                id: '12987126',
                name: '好滋好味鸡蛋仔',
                category: '江浙小吃、小吃零食',
                desc: '荷兰优质淡奶，奶香浓而不腻',
                address: '上海市普陀区真北路',
                shop: '王小虎夫妻店',
                shopId: '10333'
            }],
            // 获取row的key值
            getRowKeys(row) {
                return row.id;
            },
            // 要展开的行，数值的元素是row的key值
            expands: []
        }
    },
    mounted() {
        // 在这里你想初始化的时候展开哪一行都可以了
        this.expands.push(this.tableData5[1].id);
    }
}
</script>

<style lang="css">
.demo-table-expand {
   font-size: 0;
}
.demo-table-expand label {
     90px;
    color: #99a9bf;
}
.demo-table-expand .el-form-item {
    margin-right: 0;
    margin-bottom: 0;
     50%;
}
</style>