Local Cache Not Updating on write when online

[cSieves]

Hi, I have a method that updates a document in a firebase collection using a transaction whilst online. The update succeeds but is not reflected in the cache on subsequent reads until I read again from the server. Is this expected behaviour?

My understanding is that writes should be reflected in the cache instantly but is this not the case for transactions?

Version 21.x.x

[mikehardy]

Hmm 🤔 transactions only work online, I know that, they do not use the cache. Are you specifying a cache read after a (server-only) transaction update, via some specific parameter?

A reproduction might help with this, as well as some information about what platform(s) it happens on

[cSieves]

Hey Mike, thanks for getting back to me!

Are you specifying a cache read after a (server-only) transaction update, via some specific parameter?

Yes, I specifically call the cache. I call the cache first for nearly all my reads and then fire a request to the server, this is to enhance the user experience and reduce load times waiting for data. Specifically I use get({source: "cache" }).

The platform is IOS and this is the offending code;

   await firestore().runTransaction(async (transaction) => {
        const carDoc = await transaction.get(carDocRef);
        if (!carDoc.exists) {
            throw new Error("Car does not exist.");
        }

        const carLikes = carDoc.data().likes || [];
        if (!carLikes.includes(userId)) {
            throw new Error("Car not liked currently.");
        }

        transaction.update(carDocRef, {likes: firestore.FieldValue.arrayRemove(userId)});

        const carOwnerId = carDoc.data().carOwner;

        if (carOwnerId && carOwnerId !== userId) {
            await removeNotification(carOwnerId, {
                type: 'likedYourCar',
                userId: userId,  
                cardId: cardDod.id,   
            });
        }
    });

This code successfully runs and updates the data correctly on the server, but when I query the cache (using source: "cache") it returns the old stale data. The cache then updates once I query the server, so its not the end of the world, but I was under the impression that any writes to the server whilst online would also be reflected in the local cache. But I could be wrong there as I can't actually find where I read that

[mikehardy]

I was unable to find any related documentation personally, that is, it appears to be unspecified what the interaction is between local firestore cache and firestore transactions, other than the specification that transactions are "online only" (but it doesn't say server only). This might be a good question for a firestore-ios-sdk guru if you post it in that repo. I wasn't able to find anything on stackoverflow either

In the meantime, looks like you'll need to do a "get" on any docs updated in the transaction after the transaction completes, in order for your cache-first strategy to work after "all transaction-related activity" (where I invented that phrase, and am using it to include the transaction itself, and then the read of any related docs so they are cached)