How does type extension work?

[tonyxiao]

I see some commits that adds the following syntax

type Hello {
  world: String
}
extend type Hello {
  world2: String
}

However I can't find any docs around just what it is and how to use it. And if I actually try to use it in code I get the following message.

Error: Client Schema cannot be used for execution.

Can someone clarify how to use type extension in GraphQL?

[robzhu]

Hey @tonyxiao, can you please post the code you're running to execute type extension?

[tonyxiao]

Hmm I was using it together with ApolloStack. apollostack.com Maybe they are using an older version of graphql js and that's why there's error?

[stubailo]

Sounds like it should be an issue on graphql-tools? https://github.com/apollostack/graphql-tools

I'd close the one here.

[robzhu]

Closing this since I haven't seen any movement on this for a while. @tonyxiao, please feel free to re-open if feel there's something specific and actionable we can do in this repo.

[stubailo]

feel free to open an issue on graphql tools about documenting this.

[dyst5422]

I'm still seeing extend not work at all with graphql or express-graphql. Minimal failing example attached.

import { buildSchema, graphql } from 'graphql';

const schema = buildSchema(`
type QuerySubset {
  hello: String
}

type Queries {
  querySubset: QuerySubset
}

extend type Queries {
  hello: String
}

type Query {
  Queries: Queries
}

schema {
  query: Query
}
`)

const rootResolver = {
  Queries: {
    querySubset: {
      hello: () => 'hello world',
    },
    hello: () => 'hello world',
  }
};

// Works fine
graphql(schema, `{ Queries { querySubset { hello } } }`, rootResolver).then(response => {
  console.log(response);
})

// Errors out with 'Cannot query field "hello" on type "Queries".'
graphql(schema, `{ Queries { hello } }`, rootResolver).then(response => {
  console.log(response);
})

[krabbypattified]

Why is this closed? I would like to know how the extend keyword works and it's not documented.

[dyst5422]

@krabbypattified See the closed issue #892 and associated issue #922

[dandv]

TL;DR - use graphql-tools for now.