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I’ve designed a variety of GraphQL schemas and developed microservice backends. But not done much with configuring the Apollo implementation of a GraphQL server until recently. This may reflect the fact my understanding of JavaScript doesn’t extend into the world of Node.JS as much as I’d like (the problem with being a multi-language developer is you’re likely to find your way around many languages but never be a master of one). Anyway, the following content is about the implementation within a GraphQL server part of a solution. It may be these pointers are just for my benefit you might find them helpful as well.

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To make it easy to reference the code, we’ve added entries (n) into the code, where n is a number. This is not part of the code. But there to make the different lines referenceable. Where code should go but is not relevant to the point being made I’ve added ellipsis ()

Dynamic loading and server configuration

import { ApolloServer } from 'apollo-server';
import { loadFilesSync } from '@graphql-tools/load-files';
import { resolvers } from './resolvers.js';   (1)
import ProviderInternalAPI from './ProviderInternalAPI.js'; (1)
import EventsInternalAPI from './EventsInternalAPI.js';  (1)
const server = new ApolloServer({
  debug : true,    (2)
  typeDefs: loadFilesSync('./schema.graphql'),   (3)
  resolvers,
  dataSources: () => {
    return {
      eventsInternalAPI: new EventsInternalAPI(),    (4)
      providerInternalAPI: new ProviderInternalAPI() (4)
      pro
    };
  }});

There is the potential to dynamically load the resolvers rather than importing each JavaScript file as we see on lines (1). The mechanics to do this is documented here. It would be cool if an opinionated implementation was provided. As shown by (3) we can take a independent schema file being loaded. The Apollo example approach for this didn’t seem to work for us, although both approaches make use of graphql-tools in a synchronous manner.

We can switch on debugging (2) for the GraphQL server, although the level of information published doesn’t appear to be significant. Ideally this setting is changed for production.

Defining the resolvers

The prefix for each resolver (1) must correlate to the name in the schema of the mutator or query (not the type as you would expect with Java). Often we don’t need all the parameters for the resolver. The documentation describes replacing each unused parameter with one or more underscores (i.e _, __ ). The underscore denoting the field not in use. However we can satisfy the indication of not being used, but keep the meaning of each position by using the underscore then a name (i.e. _parent, _args ) as shown in (2).

By taking the response into a variable (3) we can optionally log it. Trying to return using invocation line would result in the handler object rather than the payload itself. By taking the result into a variable we can log the content if desired and return the content.

The use of the backward quote is a node feature. It allows us to incorporate variables into a string by referencing it within ${} (4).

We need to supply the GraphQL server with instances with a layer of code that will interact with the resolvers. We can instantiate the instances in the declaration. The naming of the object is important (4) to the resolver.js (declarations).

import { useLogger } from "@graphql-yoga/node";
...
latestEvent (1): async (_parent, _args, { dataSources }, _info) (2)   => {
      if (log) { console.log("resolvers - get latest event"); }
      let responseValue = await dataSources.eventsInternalAPI.getLatestEvent(); (3)
      if (log) { console.log(`(4)  Resolver response for latest event:\n ${responseValue}`); }
      return responseValue;
    },

Resolver declarations

 Query: {  ...
 },
  
Mutation: {...
},
  Event: {  (1)
    providers: (event, args, { dataSources }, info) => {
      if (log) { console.log(`going to locate ${event.sources}`) }
      let responseValue = await (2) dataSources.providerInternalAPI.getProviders(event.sources);
      return responseValue;
    }

To handle the use of resolvers within a larger resolver we need to declare the resolution outside of the Query and Mutator blocks (but inside the whole declaration block)(1). The name provided needs to match the parent entity that the query resolver contributes to.

To then provide values from the outer resolution we need to prover to the chained resolution use the naming as represented in the GraphQL schema as shown by (2). The GraphQL engine will resolve the mapping values.

Web resolver URL

  // GET
  async getProvider(code) {
    console.log("getProvider (%s) directing to %s",code,this.baseURL);
    return this.get(`provider?code=${code} (1)`);
  }

The URL parameters need to be appended to the base URL path for the parent class to use in the invocation as shown by (1). The Apollo examples showed a setter option but we didn’t see the URI being addressed properly. This approach produces the relevant requirement.