如图：当点击确定后，更新数据库，在数据库增加一个字段，在JS中能够成功添加，当在云函数中实现时，添加不了

在这段代码中，能够成功添加：

confirm(e){
        const that = this;
        console.log(e);
        const itmelength = that.data.code;
        const id = that.data.id;
        const wehicles = that.data.wehicles;
        db.collection("wehicle").doc(id).update({
            data:{
                top:{
                    itmelength:itmelength,
                    pud_data:new Date(), 
                }
            }
        })
        .then(res => {
            console.log(res);
        })
    }, 

在云函数中添加不了：

// 云函数入口函数
exports.main = async (event, context) => {
    const wxContext = cloud.getWXContext();
    const openid = wxContext.OPENID;
    const itmelength = event.itmelength;
    const id = event.id;
    console.log(id);
    return await db.collection("wehicle").doc(id).update({
        data:{
            "top":_.push({
               itmelength:itmelength,
               pud_data:new Date(),
            })
        }
    })
}
js代码：
confirm(e){
        const that = this;
        console.log(e);
        const itmelength = that.data.code;
        const id = that.data.id;
        const wehicles = that.data.wehicles;
        wx.cloud.callFunction({
            name:'topping',
            data:{
                top:{
                   itmelength:itmelength,
                }
            },
            success:res => {
                console.log(res);
            }
        })
}