Interface support

[andreas]

See:

• https://facebook.github.io/graphql/#sec-Interfaces
• https://facebook.github.io/graphql/#sec-Interface
• https://facebook.github.io/graphql/#sec-Field-Selections-on-Objects-Interfaces-and-Unions-Types

[sgrove]

We're coming against a use case where we need interfaces as well, any thoughts on how to support this?

[andreas]

I have some ideas, but it's not straight forward. Could unions be used to solve the use case? I think they will be easier to implement.

[sgrove]

From the spec and https://medium.com/the-graphqlhub/graphql-tour-interfaces-and-unions-7dd5be35de0d, it looks like it. I gave a bit of an example in #33 (comment), where we might have a number of Urls returned in a resolver, but as different types (VideoUrl, CommentUrl, PlainUrl, DescriptionUrl), and want to be able to traverse differently depending on the type:

{
  urls {
    __typename
    ... on VideoUrl {
      url {
        expandedText
        displayedText
        description
      }
      video {
        title
        user {
          email
        }
      }
    }
    ... on CommentUrl {
      url {
        expandedText
        displayedText
        description
      }
      comment {
        body
        created_at
        user {
          email
        }
      }
    }
    ... on PlainUrl {
      url {
        expandedText
        displayedText
        description
      }
    }
  }
}

Looks like the ... on <__typename works already, but I'm not sure how to return different types from a resolver.

[donut]

Updated links:

• https://facebook.github.io/graphql/October2016/#sec-Interfaces
• https://facebook.github.io/graphql/October2016/#sec-Interface
• https://facebook.github.io/graphql/October2016/#sec-Field-Selections-on-Objects-Interfaces-and-Unions-Types