subscribeToMore not rerendering component when watchQuery's fetchPolicy is set to no-cache

[evenfrost]

Intended outcome:

Using subscribeToMore with watchQuery's fetchPolicy set to no-cache properly rerenders the component on new subscription data arrival.

Actual outcome:

Using subscribeToMore with watchQuery's fetchPolicy set to no-cache doesn't rerender the component on new subscription data arrival.

How to reproduce the issue:

// index.ts
const defaultOptions: DefaultOptions = {
  watchQuery: {
    fetchPolicy: 'network-only',
    errorPolicy: 'all',
  },
  query: {
    fetchPolicy: 'no-cache', // if set to 'network-only', it works
    errorPolicy: 'all',
  },
  mutate: {
    errorPolicy: 'all',
  },
};

const client = new ApolloClient({
  defaultOptions,
  // ...
});

// Component.tsx

  const {
    data,
    subscribeToMore,
  } = useQuery<Data>(query, {
    variables: {
      id,
    },
  });
  
  useEffect(() => {
      const unsubscribe = subscribeToMore({
        document: subscription,
        variables: { id },
        updateQuery: (prev, { subscriptionData: { data: subscriptionData } }) => {
          if (!subscriptionData) {
            return prev;
          }

          console.log('subscriptionData', subscriptionData); // logged in both scenarios

          return {
            name: {
              ...prev.name,
              ...subscriptionData.name,
            },
          };
        },
      });

      return () => unsubscribe();
  // eslint-disable-next-line react-hooks/exhaustive-deps
  }, [])
  
// component doesn't rerender on new subscription data arrival

Versions

  System:
    OS: Linux 5.4 Ubuntu 20.04.2 LTS (Focal Fossa)
  Binaries:
    Node: 14.16.0 - ~/.nvm/versions/node/v14.16.0/bin/node
    Yarn: 1.12.3 - /usr/bin/yarn
    npm: 6.14.11 - ~/.nvm/versions/node/v14.16.0/bin/npm
  Browsers:
    Chrome: 90.0.4430.72
    Firefox: 87.0
  npmPackages:
    @apollo/client: ^3.3.15 => 3.3.15 
    apollo-client: ^2.6.10 => 2.6.10 
    apollo-server: ^2.23.0 => 2.23.0 
    apollo-server-koa: ^2.23.0 => 2.23.0 
    apollo-utilities: ^1.3.4 => 1.3.4 

[jerelmiller]

Hey @evenfrost 👋

Thanks for your patience on a response!

updateQuery is a cache write API so this is expected behavior. Your query doesn't rerender because it doesn't respond to cache update when using the no-cache fetch policy. This would explain why switching to network-only will fix the issue.

Totally understand the confusion here since the name updateQuery is a bit misleading here. You'll have to switch to one of the other fetch policies if you want this to work as you expect. Unfortunately it is a breaking change at this point to switch this behavior.

I've noted this down as a potential for improvement in a future major. If you have ideas on how you might see this change, feel free to open a feature request so we can track it. I'm going to go ahead and close this issue since there is nothing more actionable for us to look at. Thanks!

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