'useQuery' never returns data for entries written to the cache with 'writeFragment'

[limekiln]

Summary:
Because of performance problems with the InMemoryCache, I tried to migrate our app to the hermes cache. Since cache initialization was done via writeData before I changed it to use writeFragment.

So the init function would look something like:

const initCache = cache => {
  let fragmentString = gql`
    fragment test on MyType {
      ...myTypeFragment
    }
    ${fragments.myTypeFragment}
`;
let fragment = {
  id: "myType",
  fragment: fragmentString,
  fragmentName: "test"
  data: {
    __typename: "MyType",
    ...
  }
};
cache.writeFragment(fragment);

The used fragment is part of a collection of fragments and has the following structure:

const fragments = {
  myType: gql`
    fragment myTypeFragment on myType {
      __typename,
      ...
  `,
  ...
}

Using the Apollo dev tools, I can see the following entries getting created in the cache:

"ROOT_QUERY": {
  "data": {
    "myType": null
  }
}
"myType": {
  "data": {
    "__typename": "MyType",
    ...
  }
}

The myType entry looks fine, but the ROOT_QUERY entry is always null. There does not seem to be any reference between them either.

Expected Behavior:

Using

const data = useQuery(GET_MY_TYPE, { onCompleted: data => console.log(Data) });

with

const GET_MY_TYPE = gql`
  query getMyType {
    myType @client {
      ...myTypeFragment
    }
  }
  ${fragments.myTypeFragment}
`;

I expected to see a logging message containing the data from the myType entry in the cache. Executing this query within GraphiQL should also produce this result

Actual Behavior:

Instead, onCompleted is never called. Executing the query within GraphiQL returns

{
  "data": {
    "myType": null
  }
}

System Information

• OS:
  • Linux 5.0 Ubuntu 19.04 (Disco Dingo)
• Binaries:
  • Node: 13.5.0 - /usr/local/bin/node
  • npm: 6.13.4 - /usr/local/bin/npm
• Browsers:
  • Firefox: 71.0
• npmPackages:
  • @apollo/react-hooks: 3.1.3 => 3.1.3
  • apollo-cache-hermes: ^0.8.10 => 0.8.10
  • apollo-cache-inmemory: ^1.6.5 => 1.6.5
  • apollo-client: ^2.6.8 => 2.6.8
  • apollo-link: ^1.2.13 => 1.2.13
  • apollo-link-error: ^1.1.12 => 1.1.12
  • apollo-link-http: ^1.5.16 => 1.5.16
  • react-apollo: 3.1.3 => 3.1.3