mongo aggregate

const getOrderById = (_id)=> {
		return new Promise((resolve, reject)=>{
			order_item_mongo.aggregate([{
					$match: {order_id: id}
				}, {
					$group : {
						// _id  : "$menu_id",
						_id: { menu_id:"$menu_id", menu_name:"$menu_name"},
						products: { $push:  { product_name: "$product_name"} }
					}
				}], (err, docs) => {
					if (docs) {
						resolve(docs)
					}else{
						reject('get group orderitem fail')
					}
				});
		})
	}