CODEWITHSUNDEEP
firebaseflutterdartgoogle-cloud-firestore
Alb
Alb

Reputation: 1125

Only download changed/updated documents from Firestore

being new to firestore, I am trying to keep the number of downloads of documents as small as possible. I figured that I could download documents only once and store them offline. If something is changed in the cloud, download a new copy and replace the offline version of that document (give relevant documents a timestamp of last-change and download when the local version is older). I haven't started with this yet but I am going to assume something like this must already exist, right?

I'm not sure where to start and google isn't giving me many answers with the exception of enablePersistence() from the FirebaseFirestore instance. I have a feeling that this is not the thing I am looking for since it would be weird to artificially turn the network on and off for every time I want to check for changes.

Am I missing something or am I about to discover an optimisation solution to this problem?

Upvotes: 0

Views: 304

Answers (1)

Doug Stevenson
Doug Stevenson

Reputation: 317467

What you're describing isn't something that's built in to Firestore. You're going to have to design and build it using Firestore capabilities that you read in the documentation. Persistence is enabled by default, but that's not going to solve your problem, which is rather broadly stated here.

The bottom line is that neither Firestore nor its local cache have an understanding of optimizing the download of only documents that have changed, by whatever definition of "change" that you choose. When you query Firestore, it will, by default, always go to the server and download the full set of documents that match your query. If you want to query only the local cache, you can do that as well, but it will not consult the server or be aware of any changes. These capabilities are not sufficient for the optimizations you describe.

If you want to get only document changes since the last time you queried, you're going to have to design your data so that you can make such a query, perhaps by adding a timestamp field to each document, and use that to query for documents that have changed since the last time you made a query. You might also need to manage your own local cache, since the SDK's local cache might not be flexible enough for what you want.

I recommend that you read this blog post that describes in more detail how the local cache actually works, and how you might take advantage of it (or not).

Upvotes: 1

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