Firebase-ios-sdk: FR: ServerValue.increment, ServerValue.decrement

Created on 13 Sep 2017 · 2Comments · Source: firebase/firebase-ios-sdk

Extend ServerValue

Introduction

We may use Transaction when using Firebase Realtime Database. I think most of its use is a case of operating continuous values.
Since there are many restrictions on Transaction, I thought that it was better to solve with Server's Queue System.
We propose to extend ServerValue there.

Proposed solution

Increment the number saved in the Firebase Realtime Database.
If the value is not saved, set it to 1

ServerValue.increment(Value)

Decrement the number saved in Firebase Realtime Database.

ServerValue.decrement(Value)

or Calcurate

ServerValue.calcurate(Value)

Why

In Firebase it is necessary to use Transaction when operating Increment.
Save data as transactions

Transaction will lock a node.
When updating multiple data simultaneously on different nodes, performance will be degraded because it is necessary to lock at the upper node.
Also, as the amount of data increases, it is necessary to transfer a large amount of snapshots.

Usage

For example

__Before__

ref.runTransactionBlock({ (currentData: MutableData) -> TransactionResult in
  if var post = currentData.value as? [String : AnyObject], let uid = Auth.auth().currentUser?.uid {
    var stars: Dictionary<String, Bool>
    stars = post["stars"] as? [String : Bool] ?? [:]
    var starCount = post["starCount"] as? Int ?? 0
    if let _ = stars[uid] {
      // Unstar the post and remove self from stars
      starCount -= 1
      stars.removeValue(forKey: uid)
    } else {
      // Star the post and add self to stars
      starCount += 1
      stars[uid] = true
    }
    post["starCount"] = starCount as AnyObject?
    post["stars"] = stars as AnyObject?

    // Set value and report transaction success
    currentData.value = post

    return TransactionResult.success(withValue: currentData)
  }
  return TransactionResult.success(withValue: currentData)
}) { (error, committed, snapshot) in
  if let error = error {
    print(error.localizedDescription)
  }
}

__After__

let userID: String = Auth.auth().currentUser!.uid
let values: [AnyHashable: Any] = [
    "/user/stars/\(userID)": true,
    "/user/starCount": ServerValue.increment(1)
]
Database.database().reference().updateChildValues(values) { (error, ref) in
    if let error = error {
    print(error.localizedDescription)
  }
}

Although I can not do it only by changing the client, I would like you to introduce it

database feature request

Source