Ggtcf

What I'm trying to do is -

I'm getting a click from users on different clients,

and I need to know which one was the first to click.

I have a document that clients write to,

and my idea was to let clients change it, as long as it's an empty string.

Otherwise, if it's already filled (with a user id), you cannot apply a change.

This way, I'll be able to know which user has clicked first.

The problem with this solution, is that it's client sided,

and there's a slight delay, causing users that didn't click first,

to update their user id, because when they clicked, the real first user wasn't updated yet.

Now, I'm new to firestore & firebase, and my question is,

is there a way to overcome this problem?

I had another idea, to basically let all clients send current time to firestore,

and then check who is first, but I wonder if there's a way to go with my first idea, and make it work.

thx!

I think you could benefit from the atomicity of transactions (https://firebase.google.com/docs/firestore/manage-data/transactions)

The transaction would look like this:

• read the string field


• if it is empty, write and return a 'first in success', if it is not, return a 'someone already there'


• If someone is already doing a transaction on this field, retry the transaction until the other transaction is terminated (firestore will automatically do that for you)

I would go with the date validation, but doing it on the client side wouldn't be very safe, because variations in local times could cause users to incorrectly be identified as early or late. To solve that I see two options:

1. The first one would be creating an HTTPS Cloud Function where you could get the server date and send it to the database. That way you are not influenced by the local date on your users' devices. You could also do the same by hosting this code anywhere you want and calling it with HTTP, the Cloud Function is just easier.




2. The other option would be first saving the date and the user to Realtime DB. It was created for realtime applications, so it will probably be faster than Firestore to write. You can then create a DB Cloud Function that would get the date and send it to Firestore, and there you can validate which user saved first.