Schedule function in firebase

Question

The problem

I have a firebase application in combination with Ionic. I want the user to create a group and define a time, when the group is about to be deleted automatically. My first idea was to create a setTimeout(), save it and override it whenever the user changes the time. But as I have read, setTimeout() is a bad solution when used for long durations (because of the firebase billing service). Later I have heard about Cron, but as far as I have seen, Cron only allows to call functions at a specific time, not relative to a given time (eg 1 hour from now). Ideally, the user can define any given time with a datetime picker.

My idea

So my idea is as following:

1. User defines the date via native datepicker and the hour via some spinner
2. The client writes the time into a seperate firebase-database with a reference of following form: /scheduledJobs/{date}/{hour}/{groupId}
3. Every hour, the Cron task will check all the groups at the given location and delete them
4. If a user plans to change the time, he will just delete the old value in scheduledJobs and create a new one

My question

What is the best way to schedule the automatic deletion of the group? I am not sure if my approach suits well, since querying for the date may create a very flat and long list in my database. Also, my approach is limited in a way, that only full hours can be taken as the time of deletion and not any given time. Additionally I will need two inputs (date + hour) from the user instead of just using a datetime (which also provides me the minutes).

Answer 1

I believe what you're looking for is node schedule . Basically, it allows you to run serverside cron jobs, it has the ability to take date-time objects and schedule the job at that time. Since I'm assuming you're running a server for this, this would allow you to schedule the deletion at whatever time you wish based on the user input.

Answer 2

An alternative to TheCog's answer (which relies on running a node server) is to use Cloud Functions for Firebase in combination with a third party server (eg cron-jobs.org) to schedule their execution. See this video for more or this blog post for an alternative trigger.

In either of these approaches I recommend keeping only upcoming triggers in your database. So delete the jobs after you've processed them. That way you know it won't grow forever, but rather will have some sort of fixed size. In fact, you can query it quite efficiently because you know that you only need to read jobs that are scheduled before the next trigger time.

If you're having problems implementing your approach, I recommend sharing the minimum code that reproduces where you're stuck as it will be easier to give concrete help that way.