Offline Write Support & Sync in Plugin.Firebase.Firestore

[herczegzoltan]

Hi everyone 👋

I'm currently using Plugin.Firebase.Firestore in a .NET MAUI project, and I have a question regarding offline support for write operations.

Is there a recommended way to ensure that if I save data using SetDataAsync while the device is offline, and then close and reopen the app, the data will still sync once the device is back online?

I was considering storing the writes locally in a JSON file or using something like LiteDB to queue changes. Then, on app startup or when the network reconnects, I could push those changes to Firestore.

Does anyone have a better approach or best practices for this use case?

The goal is to allow the app to be used completely offline — even across restarts — and then automatically sync all changes to Firestore when an internet connection is available.

Thanks in advance! 🙏

[Kapusch]

Hi @AdamEssenmacher , @TobiasBuchholz ,

This is an interesting one we could eventually describe in the doc of Firestore implementation, what do you think?
By the way @herczegzoltan , I see you closed the question as resolved, but you didn't comment, have you finally found an answer? If yes, can you please share to the community?

[herczegzoltan]

Well during testing I figured it out it does it automatically I do not need any additional logic. It caches and if there is any change it does the sync as well.

[Kapusch]

By the way @herczegzoltan , have you encountered this FirebaseException while running in offline mode?

Failed to get document from cache. (However, this document may exist on the server. Run again without setting source to FirestoreSourceCache to attempt to retrieve the document …)

This should be fine if a document has never been locally cached (e.g. fresh app install) and we assume it's a simple cache miss. However, as per firebase/firebase-android-sdk#173, this exception can be raised for multiple reasons, among which "Document is in an unknown state", which could be a problem that we'd want to handle.

Unfortunately from what I can see while catching the FirebaseException, there is no InnerException and no accessible error code on the exception instance to positively classify this as benign cache miss.

@TobiasBuchholz or @AdamEssenmacher , do you know if this is the expected behaviour of the plugin? If yes, shouldn't we surface a stable error code (e.g. FirestoreError.NotFoundFromCache) or attach the InnerException so consumers can discriminate safe cache miss vs genuine failure?