Firebase AfterSave function like Parse.com

Question

So I was using Parse.com AfterSave cloud code function to keep a list of the most recent Posts relating to a specific location. The reason for this is to get the most recent

Answer 1

A couple of thoughts; one of which you already mentioned as 'no' but wanted to include it for completeness:

all_messages
  message_0
    message: blah blah
    timestamp: the timestamp
  message_1
    message: blah blah
    timestamp: the timestamp
  message_2
    message: blah blah
    timestamp: the timestamp

If all clients are observing the all_messages node, any time a new message is added, the clients will be notified and can query for the last three messages by timestamp. Pretty simple solution.

Another thought is to have a node that keeps a reference to just the last three messages, reducing overhead and sorting.

all_messages
  message_45
    message: blah blah
  message_50
    message: blah blah
  message_51
    message: blah blah

last_three_messages
  last_message_0: message_45
  last_message_1: message_50
  last_message_2: message_51

When a client writes a message to the all_messages node, write a reference to it in the last_three_messages node and shuffle the older messages down.

With this, clients can just observe the last_three_messages node.

It will take a little client logic to handle pushing the most current message onto the last_message_0 slot and then shuffling the other down but it would only take a few lines of code with minimal overhead.

Answer 2

There is currently no way to run your code on Firebase's servers. So you will have to come up with a less-direct mapping of Cloud Code to a new solution. Running the functionality on each client is one option, running it on a cheap "bot"/server is another one.

I'll find a few questions where this has been covered before and link them here:

• Firebase and backend logic (recent question that covers using a nodejs server)
• How would I run server-side code in Firebase?
• How do I use Firebase to handle automatic server-side calculations?
• Firebase and indexing/search
• Server Side Calculation using Firebase (which leads to four more questions about this)

One thing to keep in mind is that running a server like this is not the type of "writing a server" that you're immediately thinking of. Most of these act more like a "bot" that interacts with Firebase in the same way as your client-side code does. The only difference in that case is that it runs on an environment you control, so that it can run with elevated credentials.