Displaying all posts using Firebase in Swift? - swift

Question

My goal is so that when users open the app they will see every post from every user of the app. My data tree is as follows:
- posts
- UID
- postKey
--attributes
- users
- UID
- attributes
Here's an example:
-posts
-74anqEXU8kQHVr7IKoO3N9NNqDh1
-MLzvs5VvXB_z7fhbh2p
created_at: 1605242945.969368
image_height: 414.6865671641791
image_url: "https://firebasestorage...."
-MLzvun01fNXNRbn7TPv
-MM7zGyZ7GbenhlisJUZ
-VGxqdzc2CkWWn39pa8xUofEWgNm2
-pNvGg84JR0TbXvS4XlX8KbfBasz2
-users
-74anqEXU8kQHVr7IKoO3N9NNqDh1
-VGxqdzc2CkWWn39pa8xUofEWgNm2
I know I have to make a snapshot of all the posts, and then display it in viewDidLoad() of the main controller (SearchViewController). I can't figure out how to display all posts.
This code works for displaying the Current User's posts, stored in a file called UserService.swift:
static func posts(for user: User, completion: #escaping ([Post]) -> Void) {
let ref = Database.database().reference().child("posts").child(user.uid)
ref.observeSingleEvent(of: .value, with: { (snapshot) in
guard let snapshot = snapshot.children.allObjects as? [DataSnapshot] else {
return completion([])
}
let dispatchGroup = DispatchGroup()
let posts: [Post] = snapshot.reversed().compactMap {
guard let post = Post(snapshot: $0) else { return nil }
dispatchGroup.enter()
SaveService.isPostSaved(post) { (isSaved) in
post.isSaved = isSaved
dispatchGroup.leave()
}
return post
}
dispatchGroup.notify(queue: .main, execute: {
completion(posts)
})
})
}
And then in ViewDidLoad() of SearchViewController:
UserService.posts(for: User.current) { (posts) in
self.posts = posts
self.tableView.reloadData()
}
But how do I do this for all posts. When I try the following, it won't let me specify a random user:
let ref = Database.database().reference().child("posts").child(User)
Any idea what I can put in the ".child(User" box to make this work? Or how to create a for-loop to properly iterate through?
*EDIT
Here is what worked:
static func allPosts(completion: #escaping ([Post]) -> Void) {
let ref = Database.database().reference().child("posts")
ref.observeSingleEvent(of: .value, with: { (snapshot) in
var postsArray = [Post]()
for userSnapshot in snapshot.children {
guard let snapshot = (userSnapshot as AnyObject).children.allObjects as? [DataSnapshot] else {
return completion([])
}
let dispatchGroup = DispatchGroup()
let posts: [Post] = snapshot.reversed().compactMap {
guard let post = Post(snapshot: $0) else { return nil }
postsArray
postsArray.append(post)
dispatchGroup.enter()
SaveService.isPostSaved(post) { (isSaved) in
post.isSaved = isSaved
dispatchGroup.leave()
}
return post
}
dispatchGroup.notify(queue: .main, execute: {
completion(postsArray)
})
}
})
}

Answer 1

I may be overlooking something but it appears the goal is to
when users open the app they will see every post from every user
If that's the case, sometimes simpler is better; load all of the posts, iterate over them creating your Post object for each then reload the tableview (?)
let postsRef = self.ref.child("posts") //self.ref points to my firebase
postsRef.observeSingleEvent(of: .value, with: { snapshot in
let allPosts = snapshot.children.allObjects as! [DataSnapshot]
for postSnap in allPosts {
let aPost = Post(initWithSnapshot: postSnap)
self.postsArrray.append(post) //
}
self.postTableView.reloadData()
}
This assumes your Post class has an convenience init to populate its properties from the snapshot. If so, set isSaved to true within that since the convenience init is being called with saved data.
If you're calling this when the app starts or view loads, there's no need for callbacks and dispatchQueues.

Answer 2

You can observe one level higher in the JSON, and then add an extra loop in the callback:
let ref = Database.database().reference().child("posts")
ref.observeSingleEvent(of: .value, with: { (snapshot) in
for userSnapshot in snapshot.children {
guard let snapshot = userSnapshot.children.allObjects as? [DataSnapshot] else {
return completion([])
}
let dispatchGroup = DispatchGroup()
let posts: [Post] = snapshot.reversed().compactMap {
guard let post = Post(snapshot: $0) else { return nil }
dispatchGroup.enter()
SaveService.isPostSaved(post) { (isSaved) in
post.isSaved = isSaved
dispatchGroup.leave()
}
return post
}
}
dispatchGroup.notify(queue: .main, execute: {
completion(posts)
})
})