有一个数据源对象如下，我只想监听它的 BusinessModel.model.order_type 这个值

            BusinessModel: {
                width: "100px",
                show: false,
                title: "新增",
                model: {
                    id: "",
                    order_id: "",
                    order_no: "",
                    order_type: "",
                    bill_status: "",
                    product_time: "",
                    IsScheduled: "",
                    batch_no: "",
                    supplier_id: "",
                    start_time: "",
                    end_time: "",
                    rice_type: "",
                    item_id: "",
                    qty: "",
                    path: "",
                    createby: "",
                    create_time: "",
                    update_by: "",
                    update_time: "",
                    Remark: "",
                    sort_index: "",
                    Items: [] //明细
                },
            },

在watch的时候这样写，而不是用deep

        watch: {
            'BusinessModel.model.order_type': {
                handler(val) {

                },
                immediate: true
            }
        },

写成一个字符串 'BusinessModel.model.order_type' 就好了