GraphQLInterfaceType: TypeError: Cannot read property 'name' of undefined

[nicky-lenaers]

I have two types that implement an interface:

1. project.type.ts

import {
  GraphQLObjectType
} from 'graphql';

import { ProjectFields } from './project.fields';
import { ProjectInterfaceType } from './project-interface.type';

export const ProjectType: GraphQLObjectType = new GraphQLObjectType({
  name: 'ProjectType',
  interfaces: [ProjectInterfaceType],
  description: 'GraphQL Type for Project',
  fields: ProjectFields
});

2. project-private.type.ts

import {
  GraphQLObjectType
} from 'graphql';

import { ProjectPrivateFields } from './project.fields';
import { ProjectInterfaceType } from './project-interface.type';

export const ProjectPrivateType: GraphQLObjectType = new GraphQLObjectType({
  name: 'ProjectPrivateType',
  interfaces: [ProjectInterfaceType],
  description: 'Project Private Type',
  fields: ProjectPrivateFields
});

project-interface.type.ts

import {
  GraphQLInterfaceType
} from 'graphql';

import { ProjectFields, ProjectPrivateFields } from './project.fields';
import { ProjectType } from './project.type';
import { ProjectPrivateType } from './project-private.type';

export const ProjectInterfaceType: GraphQLInterfaceType = new GraphQLInterfaceType({
  name: 'ProjectInterfaceType',
  fields: ProjectFields,
  resolveType: (data, context) => {
    return ProjectType; // <-- I need to conditionally return either ProjectType or ProjectPrivateType
  }
});

I also have the types declared in my schema:

...
export const ProjectSchema = new GraphQLSchema({
  types: [ProjectPrivateType, ProjectType, ProjectInterfaceType],
  ...
...

Whenever I change the return type from the resolveType from ProjectType to ProjectPrivateType I get the following error:

TypeError: Cannot read property 'name' of undefined
    at ...\node_modules\graphql\type\schema.js:136:52
    at Array.forEach (<anonymous>)
    at ...\node_modules\graphql\type\schema.js:135:30
    at Array.forEach (<anonymous>)
    at new GraphQLSchema (...\node_modules\graphql\type\schema.js:132:32)
    ...

Update

I found out that it seems like some circular reference not being resolved. If I simply return the name of the type as a string, it works:

import {
  GraphQLInterfaceType
} from 'graphql';

import { ProjectFields, ProjectPrivateFields } from './project.fields';
import { ProjectType } from './project.type';
import { ProjectPrivateType } from './project-private.type';

export const ProjectInterfaceType: GraphQLInterfaceType = new GraphQLInterfaceType({
  name: 'ProjectInterfaceType',
  fields: ProjectFields,
  resolveType: (data, context) => {
    return 'ProjectPrivateType'; // <-- this actually works
  }
});

[IvanGoncharov]

@nicky-lenaers You still can return object types if you would write:

export const ProjectPrivateType = new GraphQLObjectType({
  name: 'ProjectPrivateType',
  interfaces: () => [ProjectInterfaceType],
});

Arrow function will break circular reference.

In general, it's circular dependency in JS that means the only thing that could be improved in GraphQL is producing a proper error message.

[nicky-lenaers]

@IvanGoncharov That's a shame! Your solution for the arrow function works, so thanks a lot! I've spent hours trying refactored version of the codebase, didn't come up with this.

Thanks again!