Swift 如何调用变量从Firebase数据库获取值？

我的数据库结构如下所示：

"Menus" : {
    "Day1" : {
        "mealDes" : "delicious Thai food",
        "date" : "2016.10.20",
        "mealname" : "kakoon"
    },

我的代码是：

FIRDatabase.database().reference().child("Menus/Day1").observeSingleEvent(of: .value, with: {(snap) in
    if let snapDict = snap.value as? Dictionary <String, AnyObject>{
        let date = snapDict["date"] as! String

        let OrderInfo = DataService.ds.REF_ORDER
        let USERUID = FIRAuth.auth()!.currentUser!.uid
        let userinfo = OrderInfo.child(date).child(USERUID).child("data")

        userinfo.child("address").setValue("SomeRandomAddress")
        userinfo.child("phonenumber").setValue("666888")
    }
})

child("theOtherDate").setValue(date)