delegateToSchema using default executor

[timscott]

I want to delegate resolution of a field on a local schema to a remote schema. It seems like a simple use case, and I tried to follow the docs. But apparently I'm doing something wrong.

Here's my code:

const {wrapSchema, introspectSchema} = require('@graphql-tools/wrap');
const got = require('got');
const {print} = require('graphql');
const {delegateToSchema} = require('graphql-tools');

const executor = async({document, variables}) => {
  const query = typeof document === 'string' ? document : print(document);
  return got.post('http://localhost:6677/graphql', {json: {query, variables}}).json();
};

const makeRemoteSchema = async () => {
  return wrapSchema({
    schema: await introspectSchema(executor),
    executor
  });
};

const conversations = async ({id}, _, context, info) => {
  const messageIndexSchema = await makeRemoteSchema();
  const result = await delegateToSchema({
    schema: messageIndexSchema,
    operation: 'query',
    fieldName: 'conversations',
    args: {
      consultationParticipantId: id,
    },
    context,
    info
  });
  return result;
};

result is null. I can see that it is using my executor to make the introspection call, by when resolving the field it's not using my executor but the default executor instead. By stepping through the delegateToSchema code it seems like it wants schema to be a schemaConfig (here). So I tried removing wrapSchema and just returning the config shape, like so:

const makeRemoteSchema = async () => {
  return {
    schema: await introspectSchema(executor),
    executor
  };
};

Now it does use my executor, but in the executor, but the query generated from document is an empty string an variables is an empty object.

Can you see what I'm doing wrong? Thanks for the help.

[ardatan]

You don't need to wrap the schema, it will add another delegation round. You can return the subschema directly;

const { introspectSchema} = require('@graphql-tools/wrap');
const got = require('got');
const {print} = require('graphql');
const {delegateToSchema} = require('graphql-tools');

const executor = async({document, variables}) => {
  const query = typeof document === 'string' ? document : print(document);
  return got.post('http://localhost:6677/graphql', {json: {query, variables}}).json();
};

const makeRemoteSchema = async () => {
   return {
    schema: await introspectSchema(executor),
    executor };
};

const conversations = async ({id}, _, context, info) => {
  const messageIndexSchema = await makeRemoteSchema();
  const result = await delegateToSchema({
    schema: messageIndexSchema,
    operation: 'query',
    fieldName: 'conversations',
    args: {
      consultationParticipantId: id,
    },
    context,
    info
  });
  return result;
};

[timscott]

I tried another way, using stitching and schema extensions, based on this doc. The result is the same.

import {delegateToSchema} from 'graphql-tools';
import {introspectSchema} from '@graphql-tools/wrap';
import {stitchSchemas} from '@graphql-tools/stitch';
import localSchema from './local';
import {print} from 'graphql';
import got from 'got';

const executor = async ({document, variables} ) => {
  const query = typeof document === 'string' ? document : print(document);
  return got.post('http://localhost:6677/graphql', {json: {query, variables}}).json();
};

const makeSchema = async () => {
  const remoteSchema = {
    schema: await introspectSchema(executor),
    executor
  };
  return stitchSchemas({
    subschemas: [
      remoteSchema,
      localSchema
    ],
    typeDefs: `
      extend type SchedulingAttempt {
        conversations: [Conversation!]!
      }
    `,
    resolvers: {
      SchedulingAttempt: {
        conversations: {
          selectionSet: `{ id }`,
          resolve({id}, _, context, info) {
            const result = delegateToSchema({
              schema: remoteSchema,
              operation: 'query',
              fieldName: 'conversations',
              args: { consultationParticipantId: id },
              context,
              info,
            });
            return result;
          },
        }
      }
    }
  });
};

[timscott]

@ardatan - I tired that. Notice I mentioned it at the end of the initial post. It still did not work. It did call my executor, but the query was an empty string and variables was an empty object.

[timscott]

@ardatan - Hey, thanks for helping. I pasted the exact code you posted, and these are the args to the executor:

{
   "document": {
      "kind": "Document",
      "definitions": [
         {
            "kind": "OperationDefinition",
            "operation": "query",
            "variableDefinitions": [],
            "selectionSet": {
               "kind": "SelectionSet",
               "selections": []
            }
         }
      ]
   },
   "variables": {}
}

The value of print(document) is "\n".

The remote service returns Syntax Error: Unexpected <EOF> which makes sense since there's no query or variables.

It's the same with my second example, using stitching and extensions.

[timscott]

Fixed. I had both the fieldName and the argname wrong. If you get this kind of error, double check that.