Can I generate correct union types for interface fields?

[maaft]

Schema:

scalar Date

schema {
  query: Query
}

type Query {
  me: User!
  user(id: ID!): User
  allUsers: [User]
  search(term: String!): [SearchResult!]!
  myChats: [Chat!]!
}

enum Role {
  USER,
  ADMIN,
}

interface Node {
  id: ID!
}

type Foo {
  nodes: [Node!]!
}

union SearchResult = User | Chat | ChatMessage

type User implements Node {
  id: ID!
  username: String!
  email: String!
  role: Role!
}

type Chat implements Node {
  id: ID!
  users: [User!]!
  messages: [ChatMessage!]!
}

type ChatMessage implements Node {
  id: ID!
  content: String!
  time: Date!
  user: User!
}

codegen.yml

generates:
  types.ts:
    plugins:
      - typescript

types.ts

export type Maybe<T> = T | null;
export type Exact<T extends { [key: string]: unknown }> = { [K in keyof T]: T[K] };
export type MakeOptional<T, K extends keyof T> = Omit<T, K> & { [SubKey in keyof Pick<T, K>]?: Maybe<Pick<T, K>[SubKey]> };
/** All built-in and custom scalars, mapped to their actual values */
export type Scalars = {
  ID: string;
  String: string;
  Boolean: boolean;
  Int: number;
  Float: number;
  Date: any;
};


export type Query = {
  __typename?: 'Query';
  me: User;
  user?: Maybe<User>;
  allUsers?: Maybe<Array<Maybe<User>>>;
  search: Array<SearchResult>;
  myChats: Array<Chat>;
};


export type QueryUserArgs = {
  id: Scalars['ID'];
};


export type QuerySearchArgs = {
  term: Scalars['String'];
};

export enum Role {
  User = 'USER',
  Admin = 'ADMIN'
}

export type Node = {
  id: Scalars['ID'];
};

export type Foo = {
  __typename?: 'Foo';
  nodes: Array<Node>;
};

export type SearchResult = User | Chat | ChatMessage;

export type User = Node & {
  __typename?: 'User';
  id: Scalars['ID'];
  username: Scalars['String'];
  email: Scalars['String'];
  role: Role;
};

export type Chat = Node & {
  __typename?: 'Chat';
  id: Scalars['ID'];
  users: Array<User>;
  messages: Array<ChatMessage>;
};

export type ChatMessage = Node & {
  __typename?: 'ChatMessage';
  id: Scalars['ID'];
  content: Scalars['String'];
  time: Scalars['Date'];
  user: User;
};

Why is the field nodes on type Foo of type Node and not ChatMessage | Chat | User?

In the schema, Node is defined as an interface. After code generation, suddenly I can create instances of that interface in typescript which is wrong I think: You shouldn't be allowed to create instances of an interface but only of one of the implementing types.

[dotansimha]

useImplementingTypes will be available soon ;) Thank you for the PR!

[dotansimha]

Available in @graphql-codegen/[email protected]