Decoupled Firebase code

decoupledfirebaseexample.swift

//1) Have a protocol that serves as a placeholder for something that is observing updates- mainly so you can unsubscribe from updates later when you no longer need them

protocol UpdateObserving {
    
    func unsubscribe()
    
}

//1a) Implement that protocol for Firebase. It needs a ref that can unsubscribe and a handle to the specific subscription

class FirebaseObserver: UpdateObserving {
    
    private var handle: UInt
    private var firebaseReference: FIRDatabaseReference
    
    init(handle: UInt, firebaseRef: FIRDatabaseReference) {
        self.handle = handle
        self.firebaseReference = firebaseRef
    }
    
    func unsubscribe() {
        firebaseReference.removeObserver(withHandle: self.handle)
    }
}

//2) FirebaseRepository.swift: Have a repository for your Firebase calls. Anything that observes returns an UpdateObserving

func observeRecordChanges(completionBlock: @escaping ([RecordModel]) -> ()) -> UpdateObserving {
        let userID = FIRAuth.auth()?.currentUser?.uid
        
        //super-important: you always need a ref to the specific place you're subscribing to. Otherwise you can end up shutting off other subscriptions.
        let deepRef = FIRDatabase.database().reference().child("users").child(userID!).child("records")
        
        //keep the return var from your observation
        let handle = deepRef.observe(.value, with: {(snapshot) in
                                                    
            var records = [RecordModel]()
        
            for obj in snapshot.children.allObjects as! [FIRDataSnapshot] {
                let record = RecordModel(fromSnapshot: obj) //make an object to translate Firebase snapshots into something nice
                records.append(record)
            }
            completionBlock(records)
        })
        //return the observer when you're done so the consumer can unsubscribe
        return FirebaseObserver(handle: handle, firebaseRef: deepRef)
    }

//3) TableViewController.swift: subscribe to changes when your VC appears, and unsubscribe when it dissappears.

var records = [RecordModel]()
var recordObserver: UpdateObserving?
var repository = FirebaseRepository()

func viewWillAppear(_ animated: Bool) {
  self.recordObserver = self.repository.observeRecordChanges(completionBlock: { [unowned self] (records) in
      DispatchQueue.main.async { [unowned self] in
         self.records = records
         self.tableView.reloadData()
      }
}

// don't forget to clean up after yourself or things will get slow or buggy or both                                                                //
func viewWillDissappear(_ animated: Bool) {
  self.recordObserver?.unsubscribe()
}