Apollo-client: Restore API does not retain ROOT_QUERY, ROOT_MUTATION

[danReynolds]

Intended outcome:

Calling cache.gc() after the cache is restored using a tool like https://github.com/apollographql/apollo-cache-persist should not remove all entities in the cache and only remove unreachable entities.

Actual outcome:

Calling cache.gc() after the cache is restored using a tool like https://github.com/apollographql/apollo-cache-persist removes all entities in the cache.

Explanation

It looks like this happens because when you call cache.restore(data) as defined here: https://github.com/apollographql/apollo-client/blob/master/src/cache/inmemory/inMemoryCache.ts#L99

and subsequently call EntityStore replace: https://github.com/apollographql/apollo-client/blob/master/src/cache/inmemory/entityStore.ts#L238

it hydrates the cache, but never calls retain on any ID. Normally, the ROOT_QUERY is retained by a write to the store: https://github.com/apollographql/apollo-client/blob/master/src/cache/inmemory/writeToStore.ts#L114:L114

but if nothing has been written to the store yet, and gc is called immediately after a cache.restore using a tool like cache-persist, then there are no rootIds retained and the entire cache will get garbage collected.

I think the solution would be to either:

1. Default the rootIds to include ROOT_QUERY and ROOT_MUTATION on cache instantiation so that they are not lazily retained on a call to writeToStore but assumed to be desired to be retained by default
2. Retain ROOT_QUERY and ROOT_MUTATION if a call to cache.restore includes those keys at the time restore is called
3. Have downstream tools like cache-persist know that after doing a restore, they will need to retain IDs they care about like ROOT_QUERY and ROOT_MUTATION. I think this is a riskier approach, because as a user I would assume that ROOT_QUERY should be retained by default based on the documentation of cache.gc():

I think rootIds is not a familiar term to most folks in these docs and they'd assume that unreachable would mean that there are things like dangling normalized entities, not potentially the ROOT_QUERY itself.

Let me know what your thoughts are, thanks!

[benjamn]

@danReynolds Thanks for flagging this serious problem, and for writing it up so thoroughly!

I've released a partial fix (#7333) in @apollo/[email protected], with a more complete fix coming soon in v3.3.0 (#7334). The full fix seemed a little too risky for a patch release, but the v3.3 release should be coming any day now. Please let me know if you have any questions or feedback on either part of this solution.

[loteoo]

Is this still an issue in 3.3.0 ? An app I'm working on has an empty SSR initial cache (client.cache.extract() ) when upgrading from 3.2.5 to any more recent version. We're sticking to 3.2.5 for now, I think there are still issues related to this in 3.3.0.

[benjamn]

@loteoo Are you saying SSR sends down non-empty data that you restore with client.cache.restore(data), but client.cache.extract() later gives you an empty object (after cache.gc()), or do you mean SSR isn't generating any data?

[loteoo]

@benjamn I think SSR isn't generating data? Or maybe that data can't be extracted via client.cache.extract() anymore 🤔 . Sorry I'm not sure, but here's an example with more details:

let state = null;
try {
    await getDataFromTree(
        <ApolloProvider client={client}>
            <App {...props} />
        </ApolloProvider>
    );
    state = client.cache.extract();
} catch (error) {
    console.error('Error while running `getDataFromTree`', error);
}

console.log(state);
// In 3.2.5, state is populated with data from queries
// In 3.2.6 and above, it's an empty object

Sorry if I'm not sure which is the culprit here (cache.gc() or client.cache.extract() or something else ) 🙏 .

I am fairly certain it has to do with @apollo/[email protected] and above tho 🤔 .

Maybe there's an issue with the data being cleared in getDataFromTree? Should I create a seperate issue?

[benjamn]

@loteoo If you're not calling cache.gc() in that code, this issue (#7323) probably isn't the cause of your problems, but getting an empty object is definitely strange/worrisome!

A couple more questions:

1. Are you importing getDataFromTree from @apollo/client/react/ssr?
2. Are you importing ApolloProvider from @apollo/client (or @apollo/client/react/context)?

The older @apollo/react-* packages should no longer be used.

[loteoo]

@benjamn Genius, I was indeed importing getDataFromTree from @apollo/react-ssr. I switched the import to @apollo/client/react/ssr and it's working properly with newer versions (now 3.3.6)

Thanks so much and sorry for the distraction!