Showing posts from those users you follow - swift & firebase - ios

Question

I have made a following system where users can follow each other but it is not very useful at the moment. I cannot seem to get my head around how to only show the posts of the users you follow - so I am here to ask you how you would do it.
Let me just show you how the database is set up:
As you can see I have a tap called Users - in there all the users ID are stored. Whenever a user wants to follow another user, the tap Following is made and under there the user that the current user pressed follow - his/her ID is store under Following. And then the current users ID is added to the user he/she follows under Followers. Pretty simple but complicated to explain :D I hope you get where I'm going.
So now I want only to show posts of the users I am following. How would you do that? Would you do it like this: When a user is making a post it is added to his own name under a tap called Posts AND added to all the users names under PostsToFollow? I just think it would take up a lot of space in the database? Isn't there a better way to do this?
Well here is a part of my code that is getting me all of the current users followers. How can I use that code to, whenever I am creating a new post, add that to their postsToFollow?
func startObersvingDB() {
FIRDatabase.database().reference().child("Users").child(IDgotten).child("Followers").observeEventType(.Value, withBlock: { (snapshot: FIRDataSnapshot) in
var newUpdates = [FollowersStruct]()
for update in snapshot.children {
print(update)
let updateObject = FollowersStruct(snapshot: update as! FIRDataSnapshot)
newUpdates.append(updateObject)
}
self.updates = newUpdates.reverse()
self.tableView.reloadData()
}) { (error: NSError) in
print(error.description)
}
}
To Frank:
I've made this for adding the entire post to all the users that are following my user. I cannot do that because I have a like and comment button on the posts so the likes on one users posts will not be the same as other users posts and that is why I think the idea of adding the key to the post in the followers walls is great. But how do I do that?
I have made this so far, trying to accomplish what you said :-) :
let feed = Sweet(content: update, addedByUser: name!, profilePhoto: uid, likesForPost: ["user id": false], date: timePosted, category: 1, workoutComment: "", workoutTime: "")
let feedRef = FIRDatabase.database().reference().child("feed-items").childByAutoId()
feedRef.setValue(feed.toAnyObject())
FIRDatabase.database().reference().child("Users").child(uid).child("Followers").observeEventType(.Value, withBlock: { (snapshot: FIRDataSnapshot) in
var newFollowers = [FollowersStruct]()
for updateFollowers in snapshot.children {
let updateObjectFollowers = FollowersStruct(snapshot: updateFollowers as! FIRDataSnapshot)
newFollowers.append(updateObjectFollowers)
}
self.followings = newFollowers
print(self.followings.count)
for i in 0..<self.followings.count {
let followers = self.followings[i]
let feedRefFollowers = FIRDatabase.database().reference().child("Users").child(followers.Id).child("Wall").childByAutoId()
feedRefFollowers.setValue(feed.toAnyObject())
}
}) { (error: NSError) in
print(error.description)
}

Answer 1

Writing the post under the user's own name and all his follower's names is a typical example of fanning out the data. This indeed duplicates the data, but the benefit is that your read operations will be much faster and have significantly simpler code.
If you don't want to duplicate the entire post, you can also just write the key of the new post under each follower's "wall". Then when you need to show a list of posts for a user, you read their "wall" and client-side join each post. This is the approach taken by in our classic Firefeed example app.
Either of these approaches is a form of denormalization: duplicating part of your data to get better read performance.
I highly recommend reading this article on NoSQL data modeling and checking out our video series on Firebase for SQL developers. Oh... and this blog post on client-side fan-out also won't hurt.