Stitched schema does return "null" for aliased fields in union types

[xddq]

Issue workflow progress

Progress of the issue based on the Contributor Workflow

• [x] 1. The issue provides a reproduction available on Github here
• [ ] 2. A failing test has been provided
• [ ] 3. A local solution has been provided
• [ ] 4. A pull request is pending review

---

Describe the bug

• Aliased attributes in union types resolve to null instead of their correct value when using schema stitching to combine two remote schemas.
• The same query returns the correct result on the "non-stitched" schema when issued to the non-stitched schema at localhost:/4001/graphql

To Reproduce Steps to reproduce the behavior:

• checkout the github repo
• follow the README.md steps:
  • npm i && npm run start
  • gateway on localhost:4444/graphql
  • remote-1 on localhost:4001/graphql
  • remote-2 on localhost:4002/graphql
  • go to localhost:4444/graphql (the stitched schema) and query

  • query {articles {title {
    ... on TitleOne {text}
    ... on TitleTwo {renamedText: text}
    }}}

Expected behavior

• result should contain correct values. E.g.

  
  {
  "data": {
  "articles": [
    {
      "title": {
        "text": "hello world"
      }
    },
    {
      "title": {
        "renamedText": 1
      }
    },
    {
      "title": {
        "renamedText": 2
      }
    },
    {
      "title": {
        "text": "bye"
      }
    }
  ]
  }
  }

** Actual Behaviour **
- result contains "null" for aliased fields

{ "data": { "articles": [ { "title": { "text": "hello world" } }, { "title": { "renamedText": null } }, { "title": { "renamedText": null } }, { "title": { "text": "bye" } } ] } }

**Environment:**

- OS: ubuntu 18.04
- "@graphql-tools/load": "^7.5.8",
- "@graphql-tools/schema": "^8.3.8",
- "@graphql-tools/stitch": "^8.6.6",
- "@graphql-tools/url-loader": "^7.9.11",
- "@graphql-tools/wrap": "^8.4.13",
- NodeJS: v14.19.1

[yaacovCR]

Thanks for submitting this!!!

[yaacovCR]

Are you able to post what query hits the remote schema?

[xddq]

Hey @yaacovCR , thanks for the fast response.

I did add query logging and the logging results into reproduction repo

The copy pasted QueryLog.md file:

When querying the schema directly on localhost:4001/graphql

• with the query

query {articles {title {
  ... on TitleOne {text}
  ... on TitleTwo {renamedText: text}
}}}

• we get the log (on localhost:4001/graphql):

remote-1 query:  {
  articles {
    title {
      ... on TitleOne {
        text
      }
      ... on TitleTwo {
        renamedText: text
      }
    }
  }
}

remote-1 variables:  {}

When querying the stitched schema on localhost:4444/graphql

• with the query

query {articles {title {
  ... on TitleOne {text}
  ... on TitleTwo {renamedText: text}
}}}

• we get the log (on localhost:4001/graphql):

remote-1 query:  {
  articles {
    title {
      ... on TitleOne {
        text
      }
      ... on TitleTwo {
        renamedText: text
      }
      __typename
      __typename
    }
  }
}
remote-1 variables:  {}

• and on the stitched server (localhost:4444/graphql):

stitched query:  {
  articles {
    title {
      ... on TitleOne {
        text
      }
      ... on TitleTwo {
        renamedText: text
      }
    }
  }
}

stitched variables:  {}

[yaacovCR]

i tried to reproduce this with additional test and could not get it to fail.

perhaps the problem is the subschema implementation being used -- i am not familiar with it and used a local schema.

see https://github.com/ardatan/graphql-tools/pull/4396

[yaacovCR]

The queries look fine what about the remote response?

[xddq]

Mhhh, that's strange. I mean you did use subschemas as well here

I am currently trying to figure out how to log the response from the remote-1 server. Will post it once I figured it out.

Do you see any issue with the reproduction repo?

[xddq]

Log for the request-response cycle. Starting from stitched and starting from non-stitched.

• request:

query {
  articles {
    title {
      ... on TitleOne {
        text
      }
      ... on TitleTwo {
        renamedText: text
      }
    }
  }
}

log when coming from localhost:4444/graphql (stitched)

[stitched] stitched request:  {
[stitched]   articles {
[stitched]     title {
[stitched]       ... on TitleOne {
[stitched]         text
[stitched]       }
[stitched]       ... on TitleTwo {
[stitched]         renamedText: text
[stitched]       }
[stitched]     }
[stitched]   }
[stitched] }
[stitched]
[stitched] stitched variables: {}
[remote-*1] remote-1 request:  {
[remote-*1]   articles {
[remote-*1]     title {
[remote-*1]       ... on TitleOne {
[remote-*1]         text
[remote-*1]       }
[remote-*1]       ... on TitleTwo {
[remote-*1]         renamedText: text
[remote-*1]       }
[remote-*1]       __typename
[remote-*1]       __typename
[remote-*1]     }
[remote-*1]   }
[remote-*1] }
[remote-*1] remote-1 variables: {}
[remote-*1] remote-1 response: {"articles":[{"title":{"text":"hello world","__typename":"TitleOne"}},{"title":{"renamedText":1,"__typename":"TitleTwo"}},{"title":{"renamedText":2,"__typename":"TitleTwo"}},{"title":{"text":"bye","__typename":"TitleOne"}}]}
[stitched] stitched response: {"articles":[{"title":{"text":"hello world"}},{"title":{"renamedText":null}},{"title":{"renamedText":null}},{"title":{"text":"bye"}}]}

log when coming from localhost:4001/graphql (non-stitched)

[remote-*1] remote-1 request:  {
[remote-*1]   articles {
[remote-*1]     title {
[remote-*1]       ... on TitleOne {
[remote-*1]         text
[remote-*1]       }
[remote-*1]       ... on TitleTwo {
[remote-*1]         renamedText: text
[remote-*1]       }
[remote-*1]     }
[remote-*1]   }
[remote-*1] }
[remote-*1]
[remote-*1] remote-1 variables: {}
[remote-*1] remote-1 response: {"articles":[{"title":{"text":"hello world"}},{"title":{"renamedText":1}},{"title":{"renamedText":2}},{"title":{"text":"bye"}}]}

[yaacovCR]

Mhhh, that's strange. I mean you did use subschemas as well here

I used local subschemas, i mean, not local schemas. so the executor is the default executor not whatever you set up.

Do you see any issue with the reproduction repo?

Not from the brief glance, but I just looked at it enough to make a minimal reproduction. We will know more when you get the response from the remote subschema to show up.

In theory, if it can't be reproduced with local schemas, it's not a bug in stitching, it's a bug in the executor you are using => but that's just in theory. If you find anything I can fix, I would be very happy.

[xddq]

Okay so actually all that was needed was to add an executor to the subschema config. I am not yet sure how the executor works and why it is needed (since it worked without specifying one, besides the aliases on union types issue?)

I did upload the "corrected" version in the repro repo. I am not sure if this is still worth while to take a look into it for you.

Thanks a LOT for your time and your quick responses!

[Urigo]

@xddq @yaacovCR I'm not adding anything here but just trying to label it correctly. So we couldn't yet reproduce it with a failing test but we do have a reproduction on a repo right?

[xddq]

@Urigo We have a reproduction repo, yes.

But I am not sure whether this is worth to get into since I did NOT specify an exectuor for my stitched schema while the documentation clearly states that an executor is needed. here, cited 2022-04-22-20:00:00

The only real bug (in my opinion) is that it did work without me ever specifiying an executor. It only failed while trying to rename attributes inside a union type.

I think it should error out when trying to create a subschema without specifying an executor, if one is required.