fetchPolicy: cache-only return no errors when cached item is missing

Intended outcome:

I’m using useQuery with the fetchPolicy: "cache-only" with an InMemoryCache that is primed during SSR and .restore on the client:

const { loading, data, error } = useQuery(QUERY, {
  fetchPolicy: "cache-only",
  errorPolicy: "all",
})

There are a lot of queries flying around that might invalidate data. When this happens, useQuery cannot refetch the query due to the cache policy being set to cache-only (which is good), and I expect an error to be set in the result. That way the error can be tracked since this is basically a coding error.

Actual outcome: Instead of an error being set in the result, there are warnings being logged to the console and the result is:

{ data: undefined, error: undefined, loading: false }

I need to now detect this special case and log a custom error myself.

Versions

  System:
    OS: macOS 10.15.7
  Binaries:
    Node: 14.15.1 - ~/.config/nodenv/versions/14.15.1/bin/node
    Yarn: 1.22.10 - ~/code/release-page/node_modules/.bin/yarn
    npm: 6.14.8 - ~/.config/nodenv/versions/14.15.1/bin/npm
  Browsers:
    Chrome: 87.0.4280.88
    Firefox: 84.0
    Safari: 14.0
  npmPackages:
    @apollo/client: ^3.2.5 => 3.3.2
    apollo: ^2.31.2 => 2.31.2
    apollo-link-persisted-queries: ^0.2.2 => 0.2.2

[jdalegonzalez]

@jlek This is probably too late to help you but here’s my tip…

Whenever this happens to me, it’s always because a query that doesn’t request a field populates the cache and a later query asks for another field and it’s missing. The apollo client very unhelpfully drops the error on the ground even though it knows what field is missing. The gross way to figure it out is to put a breakpoint in @apollo/client/core/ObservableQuery.js around line 85 (search for diff = this.queryInfo.getDiff). You will see the return of void 0 - meaning no data for you. The diff, though, knows which fields are missing and could spit them out as console.warn - it just doesn’t. Open up the diff in the watch window and you’re set.

OR… less gross… set “returnPartialData” on your query options. Dump the output to console and compare what comes back with what you queried for. The missing fields will be the ones that are the problem. Another query will have hit the same object without asking for some of the fields.

[jsutaria]

Any updates here? Documentation says that the query should throw an error too. https://www.apollographql.com/docs/react/data/queries/#cache-only