[ibdknox]

Hey Michael! Congrats on the launch :)

Providing a one-size-fits-all solution here is probably impossible, but it seems like it would be nice to provide some mechanism to be notified that you're making edits based on stale information. If such a mechanism existed, it would be easy to add a bunch of canned merge strategies. In doing so you can probably teach people a little bit about the pitfalls they're likely to run into (these sorts of bugs are insanely difficult to track down), while not really making them do much work.

The approach we've taken in Eve is that we can't solve all these problems for you, but we can at least let you know that things can go sideways and prompt you to make a deliberate decision about what should happen. It's amazing how helpful that ends up being.

[mikelehen]

Thanks for the feedback. I think you're right and we're interested in exploring what we can do to help people more in the future. One of the really nice things about Cloud Firestore is that documents are versioned with timestamps in such a way that we could definitely detect and expose conflicts and let you decide how to deal with them... It's mostly a matter of identifying the common use cases and then figuring out the right API to make them possible without going too far into the deep end of conflict resolution.

[lozenge]

It looks to me like Firestore's API doesn't include a "default" way to upload user edits to documents. Conflict detection is possible using the transactions - https://cloud.google.com/firestore/docs/manage-data/update-d... - you can do something like HTTP's PUT If-Unmodified-Since (or PUT If-Match).

[mikelehen]

Good point. read-modify-write transactions are a good way to detect conflicts and get a chance to handle them, but they're unfortunately limited to while the client is online. If the client is offline, the transaction will fail so they're not useful for general conflict resolution. This was an intentional decision because there's not a straightforward way to preserve the intent of the transaction across app restarts. But there may be options for adding some sort of conflict resolution strategy in the future that leverages the same underlying primitives that transactions use today.