Cannot query after deleting an entity that is used in a union type

Issues GraphQL
,
1

Report a GraphQL Bug

What edition and version of Dgraph are you using?

Edition:

  • SlashGraphQL
  • Dgraph (community edition/Dgraph Cloud)

If you are using the community edition or enterprise edition of Dgraph, please list the version:

Dgraph Version 
$ dgraph version
 
v21.03.0-56-gc900f96b3

Have you tried reproducing the issue with the latest release?

Yes.

Steps to reproduce the issue (paste the query/schema if possible)

I have a schema that I use a union type:

type Page {
  PageID: ID!
  components: [Component]
}

union Component = BannerComponent | TextComponent

type BannerComponent {
  ComponentID: ID!
  banner_url: String!
}

type TextComponent {
  ComponentID: ID!
  text: String!
}

And I created two components and assigned them to a page, So when I query page:

query getPageAndComponents {
  queryPage {
    PageID
    components {
      ... on BannerComponent {
        __typename
        ComponentID
        banner_url
      }
      ... on TextComponent {
        __typename
        ComponentID
        text
      }
    }
  }
}

I get this result which is correct:

{
  "data": {
    "queryPage": [
      {
        "PageID": "0x3d4635056",
        "components": [
          {
            "__typename": "BannerComponent",
            "ComponentID": "0x3d4635055",
            "banner_url": "https://banner.jpg"
          },
          {
            "__typename": "TextComponent",
            "ComponentID": "0x3d4635057",
            "text": "sample"
          }
        ]
      }
    ]
}

Now I tried to delete one of the components:

mutation deleteTextComponent {
  deleteTextComponent(filter: {
    ComponentID: "0x3d4635057"
  }) {
    numUids
  }
}

And as expected this is the result:

{
  "data": {
    "deleteTextComponent": {
      "numUids": 1
    }
}

Now When I want to query page and its components with the same query:

query getPageAndComponents {
  queryPage {
    PageID
    components {
      ... on BannerComponent {
        __typename
        ComponentID
        banner_url
      }
      ... on TextComponent {
        __typename
        ComponentID
        text
      }
    }
  }
}

I get this error:

"errors": [
    {
      "message": "Non-nullable field 'banner_url' (type String!) was not present in result from Dgraph.  GraphQL error propagation triggered.",
      "locations": [
        {
          "line": 8,
          "column": 9
        }
      ],
      "path": [
        "queryPage",
        0,
        "components",
        1,
        "banner_url"
      ]
    }
  ],

This is the URL if you want to give it a try:
https://green-pine.us-east-1.aws.cloud.dgraph.io/graphql

Expected behaviour and actual result.

Expected Result will be:

{
  "data": {
    "queryPage": [
      {
        "PageID": "0x3d4635056",
        "components": [
          {
            "__typename": "BannerComponent",
            "ComponentID": "0x3d4635055",
            "banner_url": "https://banner.jpg"
          }
        ]
      }
    ]
  }
}
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