GraphQL circular dependencies

README.md

Circular dependencies on GraphQL schemas

Problem

Whenever I uncomment the lines on author.js I get the following error:

/Users/xicombd/Code/taskq/taskq-api/node_modules/graphql/jsutils/invariant.js:20
    throw new Error(message);
    ^

Error: Can only create List of a GraphQLType but got: undefined.
    at invariant (/Users/xicombd/Code/taskq/taskq-api/node_modules/graphql/jsutils/invariant.js:20:11)
    at new GraphQLList (/Users/xicombd/Code/taskq/taskq-api/node_modules/graphql/type/definition.js:712:39)
    at Object.<anonymous> (/Users/xicombd/Code/taskq/taskq-api/lib/schema/types/author.js:21:13)
    at Module._compile (module.js:435:26)
    at normalLoader (/Users/xicombd/Code/taskq/taskq-api/node_modules/babel-core/lib/api/register/node.js:199:5)
    at Object.require.extensions.(anonymous function) [as .js] (/Users/xicombd/Code/taskq/taskq-api/node_modules/babel-core/lib/api/register/node.js:216:7)
    at Module.load (module.js:356:32)
    at Function.Module._load (module.js:311:12)
    at Module.require (module.js:366:17)
    at require (module.js:385:17)
    at Object.<anonymous> (/Users/xicombd/Code/taskq/taskq-api/lib/schema/types/post.js:6:17)
    at Module._compile (module.js:435:26)
    at normalLoader (/Users/xicombd/Code/taskq/taskq-api/node_modules/babel-core/lib/api/register/node.js:199:5)
    at Object.require.extensions.(anonymous function) [as .js] (/Users/xicombd/Code/taskq/taskq-api/node_modules/babel-core/lib/api/register/node.js:216:7)
    at Module.load (module.js:356:32)
    at Function.Module._load (module.js:311:12)

Any ideas on how to deal with this?

EDIT: Fix

Using a function to return the fields on author.js does the trick:

On author.js
@@ -13 +13 @@
-   fields: {
+   fields: () => ({

author.js

import {
  GraphQLObjectType,
  GraphQLID,
  GraphQLString,
  GraphQLNonNull,
  // GraphQLList
} from 'graphql'

// import GraphQLPost from './post'

export default new GraphQLObjectType({
  name: 'Author',
  fields: {
    id: {
      type: new GraphQLNonNull(GraphQLID)
    },
    name: {
      type: GraphQLString
    },
    // posts: {
    //   type: new GraphQLList(GraphQLPost),
    //   resolve (parent, args) {
    //     return [
    //       {
    //         id: 'foo',
    //         name: 'Foo',
    //         content: 'foo foo foo'
    //       },
    //       {
    //         id: 'bar',
    //         name: 'Bar',
    //         content: 'bar bar bar'
    //       }
    //     ]
    //   }
    // }
  }
})

post.js

import {
  GraphQLObjectType,
  GraphQLID,
  GraphQLString,
  GraphQLNonNull
} from 'graphql'

import GraphQLAuthor from './author'

export default new GraphQLObjectType({
  name: 'Post',
  fields: {
    id: {
      type: new GraphQLNonNull(GraphQLID)
    },
    title: {
      type: GraphQLString
    },
    content: {
      type: GraphQLString
    },
    author: {
      type: GraphQLAuthor,
      resolve (parent, args) {
        return {
          id: 'john',
          name: 'John Doe'
        }
      }
    }
  }
})

shema.js

import {
  GraphQLSchema,
  GraphQLObjectType,
  GraphQLID,
  GraphQLNonNull,
  GraphQLList
} from 'graphql'

import GraphQLPost from './post'
import GraphQLAuthor from './author'

const Query = new GraphQLObjectType({
  name: 'Query',
  fields: () => ({
    posts: {
      type: new GraphQLList(GraphQLPost),
      resolve (parent, args) {
        return [
          {
            id: 'foo',
            title: 'Foo',
            content: 'foo foo foo'
          },
          {
            id: 'bar',
            title: 'Bar',
            content: 'bar bar bar'
          },
          {
            id: 'baz',
            title: 'Baz',
            content: 'baz baz baz'
          }
        ]
      }
    },
    post: {
      type: GraphQLPost,
      args: {
        id: {
          type: new GraphQLNonNull(GraphQLID)
        }
      },
      resolve (parent, {id}) {
        return {
          id: 'foo',
          title: 'Foo',
          content: 'foo foo foo'
        }
      }
    },
    authors: {
      type: new GraphQLList(GraphQLAuthor),
      resolve (parent, args) {
        return [
          {
            id: 'john',
            name: 'John Doe'
          },
          {
            id: 'jane',
            name: 'Jane Doe'
          }
        ]
      }
    },
    author: {
      type: GraphQLAuthor,
      args: {
        id: {
          type: new GraphQLNonNull(GraphQLID)
        }
      },
      resolve (parent, args) {
        return {
          id: 'john',
          name: 'John Doe'
        }
      }
    }
  })
})

const Schema = new GraphQLSchema({
  query: Query
})

export default Schema