var user:String = (Auth.auth().currentUser?.email)! // I used email as name of document.

var Groups = [String:Any]()

    let docRef = AppDelegate.db.collection("JoinedGroups").document(user)

    docRef.getDocument(source: .cache) { (document, error) in
        if let document = document {
            let dataDescription = document.data()
            self.Groups = dataDescription!   // unwrapping here
            print("Cached document data: (dataDescription)")
        } else {
            print("Document does not exist in cache")
        }
    }
    // Do any additional setup after loading the view.
    print(Groups)

}