Empty object instead of undefined when using cache redirect and cache-only fetch policy

[ziga-miklic]

Hello! 👋

In our app we have cache redirects for fields using typePolicies and toReference. Since version 3.4.8 the values the cache returns for these fields has changed during loading or if the reference is not found. The issue happens only when we use a query with fetchPolicy set to cache-only.

Intended outcome:
The data from the userQuery hook should return undefined during loading or if the reference cannot be found.

Actual outcome:
The data from the userQuery hook returns and empty object {} during loading or if the reference cannot be found.

How to reproduce the issue:
I've recreated the issue on CodeSandbox:
https://codesandbox.io/s/eager-mahavira-ie04m?file=/src/index.jsx

I've modified your template by:

• Adding a new Pet type
• Added a nested pets field to the Person type
• Changed the ALL_PEOPLE query to include pets
• Added a new SINGLE_PET query that allows you to get a Pet item by id
• Used the new SINGLE_PET query with the fetchPolicy set to cache-only
• Added a cache redirect for pet using typePolicies and toReference

Versions
3.4.8 and newer

Similar closed issue
#6368

Is this an intentional change or a regression?

Thank you for all the amazing work you've done with Apollo!

Žiga

[lxcid]

If it help this is an issue for us as well.

[Antarases]

Hi!

Is there any update concerning this issue?
I've noticed that it happens in all versions between 3.4.8 and 3.5.6.

Now I rolled back to 3.4.7.
Maybe somebody has other solution? Would like to know about it. 🙂

[ziga-miklic]

@Antarases A possible workaround: In our app, adding an if statement inside the type policy read function to check if the reference has an id field solved the issue.

For example:

typePolicies: {
  Query: {
    fields: {
      user(existingData, { args, toReference, readField }) {
        // Search and return data if it already exists.
        // https://www.apollographql.com/docs/react/caching/advanced-topics/#cache-redirects-using-field-policy-read-functions
        const reference = toReference({ __typename: 'User', id: args?.id });
        // Check if reference is not empty (regression from Apollo client since 3.4.8)
        const referenceData = reference && readField('id', reference) ? reference : undefined;

        return existingData || referenceData;
      }
    }
  }
}

[lxcid]

Bumping this up for visibility, making it hard for us to upgrade to latest.

[lxcid]

Are we gonna address this issue or should we expect empty object when dealing with cached situation now?