Firebase - Atomic writes Across Multiple Locations not working - ios

Question

How can I make this function to update the realtime database in Firebase? I managed to make the function work but only to write new ID's for posts when updateChild is triggered. How can I make it to update the current posts by their post ID?
var pathToPictures = [Pictures]()
func updateAllImagesOfCurrentUserInDatabase() {
//refrences
let ref = FIRDatabase.database().reference()
let uid = FIRAuth.auth()?.currentUser?.uid
//match the user ID value stored into posts with current userID and get all the posts of the user
let update = ref.child("posts").queryOrdered(byChild: "userID").queryEqual(toValue: uid)
update.observe(FIRDataEventType.value, with: { (snapshot) in
// print(snapshot)
self.pathToPictures.removeAll()
if snapshot.key != nil {
let results = snapshot.value as! [String : AnyObject]
for (_, value) in results {
let pathToPostPicture = Pictures()
if let pathToImage = value["pathToImage"] as? String , let postID = value["postID"] as? String {
pathToPostPicture.postImageUrl = pathToImage
pathToPostPicture.postID = postID
self.pathToPictures.append(pathToPostPicture)
print("Image and POST ID: \(pathToPostPicture.postImageUrl!)")
print("Post ID is : \(postID)")
if FIRAuth.auth()?.currentUser?.uid == uid {
ref.child("Users_Details").child(uid!).child("profileImageUrl").observeSingleEvent(of: .value, with: { (userSnapshot) in
print(userSnapshot)
let userIMageUrl = userSnapshot.value as! String
pathToPostPicture.postImageUrl = userIMageUrl
self.pathToPictures.append(pathToPostPicture)
print("This is the image path:" + userIMageUrl + String(self.pathToPictures.count))
// Generate the path
let newPostRef = ref.child("posts").childByAutoId()
let newKey = newPostRef.key as String
print(newKey)
let updatedUserData = ["posts/\(postID)/pathToImage": pathToPostPicture.postImageUrl]
print("This is THE DATA:" , updatedUserData)
ref.updateChildValues(updatedUserData as Any as! [AnyHashable : Any])
})
}
print(self.pathToPictures.count)
}
}
} else {
print("snapshot is nill")
}
self.collectionView?.reloadData()
})
}
UPDATE: This is how my database looks like
This is my database:
"Users_Details" : {
"aR0nRArjWVOhHbBFB8yUfao64z62" : {
"profileImageUrl" : "url",
"userID" : "aR0nRArjWVOhHbBFB8yUfao64z62"
},
"oGxXznrS2DS4ic1ejcSfKB5UlIQ2" : {
"profileImageUrl" : "url",
"userID" : "oGxXznrS2DS4ic1ejcSfKB5UlIQ2"
}
},
"posts" : {
"-KlzNLcofTgqJgfTaGN9" : {
"fullName" : "full name",
"interval" : 1.496785712879506E9,
"normalDate" : "Tue, 06 Jun 2017 22:48",
"pathToImage" : "url",
"userID" : "oGxXznrS2DS4ic1ejcSfKB5UlIQ2"
},
"-KlzNXfvecIwBatXxmGW" : {
"fullName" : "full name",
"interval" : 1.496785761349721E9,
"normalDate" : "Tue, 06 Jun 2017 22:49",
"pathToImage" : "url",
"userID" : "oGxXznrS2DS4ic1ejcSfKB5UlIQ2"
},
Let me tell you what it does: It's looping through the posts and finds all the current user posts. Then it takes the path to image url of every post and assign it to an array. After that it's finding the current user path to image url and updates the whole array with that. Now, I don't know how to update the database with the new values. If anybody knows it will be much appreciate it!
I am looking to make Atomic Writes Across Multiple Locations. Can somebody show me how to fix my code to do that?
It will look something like this:
// ATOMIC UPDATE HERE - IF SOMEBODY CAN FIND THE RIGHT WAY OF DOING THAT
// Generate a new push ID for the new post
let newPostRef = ref.child(byAppendingPath: "posts").childByAutoId()
let newPostKey = newPostRef.key
// Create the data we want to update
let updatedUserData = ["posts/\(newPostKey)": ["pathToImage": self.pathToPictures]] as [String : Any]
// Do a deep-path update
ref.updateChildValues(updatedUserData)

Answer 1

It looks like you're going to be downloading a lot of repetitive data. While denormalization of your database is a good practice, I would argue that in this case, you're better off not including the same download URL in every post. It doesn't make a difference across a handful of posts, but if you have thousands of users and tens or hundreds of thousands of posts, that's a lot of extra data being downloaded. Instead, you could have a dictionary containing uids as keys and the profile imageUrl as the value. You could check the dictionary for the desired uid, and if it's not present, query the database for that user's User_Details, then add them to the dictionary. When you need to display the image, you'd get the url from this dictionary. Someone else may have a better suggestion for this, so I welcome other ideas.
If you'd prefer to keep the profile image in every post, then I recommend using Cloud Functions for Firebase. You can make a function that, when profileImageUrl is updated in the user's User_Details, then updates this entry in the other posts. Currently, Cloud Functions are only available in Node.js. If you don't know JS, please don't let that be a deterrent! It's definitely worth it to learn a bit a JS. And the samples show you about as much JS as you'll have to know to get started.
Check out these resources:
Getting Started with Cloud Functions for Firebase
GitHub samples
Cloud Functions for Firebase documentation
Writing a Database Trigger
Writing a Cloud Storage Trigger: Part 1
Writing a Cloud Storage Trigger: Part 2

Answer 2

After struggling with the logic for a few days I finally got it. If anyone will encounter something like this, this is the answer. In my case it's about updating all the posts of the current user when user changes his image (my posts use denormalisation so every path to image is different). It will loop through the posts, find the current user postsID matching his UserID, place them into an array, finds the currentUser picture and update that array with the path to image. Finally will update the Firebase Database!
var pathToPictures = [Pictures]()
func updateAllImagesOfCurrentUserInDatabase() {
//refrences
let ref = FIRDatabase.database().reference()
let uid = FIRAuth.auth()?.currentUser?.uid
//match the user ID value stored into posts with current userID and get all the posts of the user
let update = ref.child("posts").queryOrdered(byChild: "userID").queryEqual(toValue: uid)
update.observe(FIRDataEventType.value, with: { (snapshot) in
self.pathToPictures.removeAll()
if snapshot.value as? [String : AnyObject] != nil {
let results = snapshot.value as! [String : AnyObject]
for (_, value) in results {
let pathToPostPicture = Pictures()
if let pathToImage = value["pathToImage"] as? String , let postID = value["postID"] as? String {
pathToPostPicture.postImageUrl = pathToImage
pathToPostPicture.postID = postID
self.pathToPictures.append(pathToPostPicture)
print("Image and POST ID: \(pathToPostPicture.postImageUrl!)")
print("Post ID is : \(postID)")
if FIRAuth.auth()?.currentUser?.uid == uid {
ref.child("Users_Details").child(uid!).child("profileImageUrl").observeSingleEvent(of: .value, with: { (userSnapshot) in
print(userSnapshot)
let userIMageUrl = userSnapshot.value as! String
pathToPostPicture.postImageUrl = userIMageUrl
self.pathToPictures.append(pathToPostPicture)
print("This is the image path:" + userIMageUrl + String(self.pathToPictures.count))
// Update the Database
let postIDCount = pathToPostPicture.postID!
let updatedUserData = ["posts/\(postIDCount)/pathToImage": pathToPostPicture.postImageUrl!]
print("This is THE DATA:" , updatedUserData)
ref.updateChildValues(updatedUserData as Any as! [AnyHashable : Any])
})
}
print(self.pathToPictures.count)
}
}
} else {
print("snapshot is nill - add some data")
}
self.collectionView?.reloadData()
})
}