graphql union type extraction fragment doesn't get mapping field values

[krrrr38]

Issue Description

When defining union type and getting these fields from fragment, apollo-client doesn't get these values.

Link to Reproduction

krrrr38/react-apollo-error-template#1

Reproduction Steps

See the reproduction PR. In this pr, graphql defines PetData union data.

union PetData = DogData | CatData

type DogData {
  dogData: String!
}

type CatData {
  dogData: String!
}

When accessing data using fragment AllPetData, apollo-client doesn't get dogData and catData.

  fragment AllPetData on PetData {
    ... on DogData {
      dogData
    }
    ... on CatData {
      catData
    }
  }
  query AllPeople {
    people {
      id
      name
      pet
      data {
        ...AllPetData
      }
    }
  }

For workaround, we should remove fragment.

  query AllPeople {
    people {
      id
      name
      pet
      data {
        ... on DogData {
          dogData
        }
        ... on CatData {
          catData
        }
      }
    }
  }

@apollo/client version

3.9.4

[phryneas]

Hi!

Have you made sure to specify possibleTypes in your cache configuration?

[krrrr38]

wow, it resolves the issue. Thank you so much for the information!

  cache: new InMemoryCache({
    possibleTypes: {
      PetData: ["CatData", "DogData"],
    }
  }),

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