How to Use GraphQL

GraphQL is a powerful query language for APIs and a runtime for executing those queries. Below is a simple example of how to set up a GraphQL endpoint and handle requests in your application.

Example: Setting Up a GraphQL Endpoint

import { route, RouteResult, ProcessedRequest } from 'router';
import { graphql, buildSchema, GraphQLError } from 'graphql';

// Define your GraphQL schema
const schema = buildSchema(`
  type Query {
    hello: String
  }
`);

// Define resolvers for your schema
const rootValue = {
  hello: () => 'Hello world!'
};

// Example with Fastify (or similar server)
const app = Fastify();

app.post('/graphql', async (req, reply) => {
  const { query, variables } = req.body as { query: string, variables?: any };
  const result = await graphql({
    schema,
    source: query,
    variableValues: variables,
    rootValue,
  });
  reply.send(result);
});

app.listen({ port: 3000 });

// Example with custom route handler
route(['GET', 'POST'], 'endpoint', async function(req: ProcessedRequest) {
  const { query, variables } = req.body as { query: string, variables?: any };
  try {
    const result = await graphql({
      schema,
      source: query,
      variableValues: variables,
      rootValue,
    });
    return new RouteResult(result, 200);
  } catch (e) {
    if (e instanceof GraphQLError) {
      return new RouteResult({ error: e.message }, 400);
    }
    throw e;
  }
});

How It Works

1. Schema Definition: You define your GraphQL schema using buildSchema. This describes the types and queries your API supports.
2. Resolvers: You provide resolver functions (like hello) that return data for each field in your schema.
3. Handling Requests: When a request comes in, you pass the query and variables to the graphql function, which executes the query against your schema and resolvers.
4. Error Handling: If a GraphQL error occurs, you can catch it and return a suitable error response.

This setup allows you to easily add a flexible GraphQL API to your application, supporting both GET and POST requests.