express-graphql

What is express-graphql?

The express-graphql package is a middleware for integrating GraphQL with an Express server. It allows you to create a GraphQL HTTP server with Express, enabling you to define a schema, resolve functions, and handle GraphQL queries and mutations.

What are express-graphql's main functionalities?

Setting up a basic GraphQL server

This code sets up a basic GraphQL server using express-graphql. It defines a simple schema with a single query 'hello' and a root resolver that returns 'Hello world!'. The server listens on port 4000 and provides a GraphiQL interface for testing queries.

const express = require('express');
const { graphqlHTTP } = require('express-graphql');
const { buildSchema } = require('graphql');

const schema = buildSchema(`
  type Query {
    hello: String
  }
`);

const root = { hello: () => 'Hello world!' };

const app = express();
app.use('/graphql', graphqlHTTP({
  schema: schema,
  rootValue: root,
  graphiql: true,
}));

app.listen(4000, () => console.log('Now browse to localhost:4000/graphql'));

Enabling GraphiQL interface

This code demonstrates how to enable the GraphiQL interface, an in-browser IDE for exploring GraphQL. By setting the 'graphiql' option to true, you can navigate to '/graphql' in your browser and interact with your GraphQL API.

const express = require('express');
const { graphqlHTTP } = require('express-graphql');
const { buildSchema } = require('graphql');

const schema = buildSchema(`
  type Query {
    hello: String
  }
`);

const root = { hello: () => 'Hello world!' };

const app = express();
app.use('/graphql', graphqlHTTP({
  schema: schema,
  rootValue: root,
  graphiql: true,
}));

app.listen(4000, () => console.log('Now browse to localhost:4000/graphql'));

Handling mutations

This code shows how to handle mutations in a GraphQL server. It defines a schema with a 'setMessage' mutation and a 'getMessage' query. The 'setMessage' mutation updates a message variable, and the 'getMessage' query retrieves the current message.

const express = require('express');
const { graphqlHTTP } = require('express-graphql');
const { buildSchema } = require('graphql');

const schema = buildSchema(`
  type Mutation {
    setMessage(message: String): String
  }
  type Query {
    getMessage: String
  }
`);

let message = 'Hello world!';

const root = {
  setMessage: ({ message: newMessage }) => {
    message = newMessage;
    return message;
  },
  getMessage: () => message,
};

const app = express();
app.use('/graphql', graphqlHTTP({
  schema: schema,
  rootValue: root,
  graphiql: true,
}));

app.listen(4000, () => console.log('Now browse to localhost:4000/graphql'));

Other packages similar to express-graphql

apollo-server-express

Apollo Server is a community-maintained open-source GraphQL server that works with various Node.js HTTP server frameworks, including Express. It provides a more feature-rich and flexible solution compared to express-graphql, with built-in support for schema stitching, subscriptions, and more.

graphql-yoga

GraphQL Yoga is a fully-featured GraphQL server with focus on easy setup, performance, and great developer experience. It is built on top of Apollo Server and Express, offering additional features like out-of-the-box support for GraphQL subscriptions and file uploads.

README

GraphQL HTTP Server Middleware

Create a GraphQL HTTP server with any HTTP web framework that supports connect styled middleware, including Connect itself, Express and Restify.

Installation

npm install --save express-graphql

Simple Setup

Just mount express-graphql as a route handler:

const express = require('express');
const graphqlHTTP = require('express-graphql');

const app = express();

app.use('/graphql', graphqlHTTP({
  schema: MyGraphQLSchema,
  graphiql: true
}));

app.listen(4000);

Setup with Restify

Use .get or .post (or both) rather than .use to configure your route handler. If you want to show GraphiQL in the browser, set graphiql: true on your .get handler.

const restify = require('restify');
const graphqlHTTP = require('express-graphql');

const app = restify.createServer();

app.post('/graphql', graphqlHTTP({
  schema: MyGraphQLSchema,
  graphiql: false
}));

app.get('/graphql', graphqlHTTP({
  schema: MyGraphQLSchema,
  graphiql: true
}));

app.listen(4000);

Options

The graphqlHTTP function accepts the following options:

• schema: A GraphQLSchema instance from GraphQL.js. A schema must be provided.

• graphiql: If true, presents GraphiQL when the GraphQL endpoint is loaded in a browser. We recommend that you set graphiql to true when your app is in development, because it's quite useful. You may or may not want it in production.

• rootValue: A value to pass as the rootValue to the graphql() function from GraphQL.js/src/execute.js.

• context: A value to pass as the context to the graphql() function from GraphQL.js/src/execute.js. If context is not provided, the request object is passed as the context.

• pretty: If true, any JSON response will be pretty-printed.

• formatError: An optional function which will be used to format any errors produced by fulfilling a GraphQL operation. If no function is provided, GraphQL's default spec-compliant formatError function will be used.

• extensions: An optional function for adding additional metadata to the GraphQL response as a key-value object. The result will be added to "extensions" field in the resulting JSON. This is often a useful place to add development time metadata such as the runtime of a query or the amount of resources consumed. This may be an async function. The function is give one object as an argument: { document, variables, operationName, result }.

• validationRules: Optional additional validation rules queries must satisfy in addition to those defined by the GraphQL spec.

In addition to an object defining each option, options can also be provided as a function (or async function) which returns this options object. This function is provided the arguments (request, response, graphQLParams) and is called after the request has been parsed.

The graphQLParams is provided as the object { query, variables, operationName, raw }.

app.use('/graphql', graphqlHTTP(async (request, response, graphQLParams) => ({
  schema: MyGraphQLSchema,
  rootValue: await someFunctionToGetRootValue(request)
  graphiql: true
})));

HTTP Usage

Once installed at a path, express-graphql will accept requests with the parameters:

• query: A string GraphQL document to be executed.

• variables: The runtime values to use for any GraphQL query variables as a JSON object.

• operationName: If the provided query contains multiple named operations, this specifies which operation should be executed. If not provided, a 400 error will be returned if the query contains multiple named operations.

• raw: If the graphiql option is enabled and the raw parameter is provided raw JSON will always be returned instead of GraphiQL even when loaded from a browser.

GraphQL will first look for each parameter in the URL's query-string:

/graphql?query=query+getUser($id:ID){user(id:$id){name}}&variables={"id":"4"}

If not found in the query-string, it will look in the POST request body.

If a previous middleware has already parsed the POST body, the request.body value will be used. Use multer or a similar middleware to add support for multipart/form-data content, which may be useful for GraphQL mutations involving uploading files. See an example using multer.

If the POST body has not yet been parsed, express-graphql will interpret it depending on the provided Content-Type header.

• application/json: the POST body will be parsed as a JSON object of parameters.

• application/x-www-form-urlencoded: this POST body will be parsed as a url-encoded string of key-value pairs.

• application/graphql: The POST body will be parsed as GraphQL query string, which provides the query parameter.

Combining with Other Express Middleware

By default, the express request is passed as the GraphQL context. Since most express middleware operates by adding extra data to the request object, this means you can use most express middleware just by inserting it before graphqlHTTP is mounted. This covers scenarios such as authenticating the user, handling file uploads, or mounting GraphQL on a dynamic endpoint.

This example uses express-session to provide GraphQL with the currently logged-in session.

const session = require('express-session');
const graphqlHTTP = require('express-graphql');

const app = express();

app.use(session({ secret: 'keyboard cat', cookie: { maxAge: 60000 }}));

app.use('/graphql', graphqlHTTP({
  schema: MySessionAwareGraphQLSchema,
  graphiql: true
}));

Then in your type definitions, you can access the request via the third "context" argument in your resolve function:

new GraphQLObjectType({
  name: 'MyType',
  fields: {
    myField: {
      type: GraphQLString,
      resolve(parentValue, args, request) {
        // use `request.session` here
      }
    }
  }
});

Providing Extensions

The GraphQL response allows for adding additional information in a response to a GraphQL query via a field in the response called "extensions". This is added by providing an extensions function when using graphqlHTTP. The function must return a JSON-serializable Object.

When called, this is provided an argument which you can use to get information about the GraphQL request:

{ document, variables, operationName, result }

This example illustrates adding the amount of time consumed by running the provided query, which could perhaps be used by your development tools.

const graphqlHTTP = require('express-graphql');

const app = express();

app.use(session({ secret: 'keyboard cat', cookie: { maxAge: 60000 }}));

app.use('/graphql', graphqlHTTP(request => {
  const startTime = Date.now();
  return {
    schema: MyGraphQLSchema,
    graphiql: true,
    extensions({ document, variables, operationName, result }) {
      return { runTime: Date.now() - startTime };
    }
  };
}));

When querying this endpoint, it would include this information in the result, for example:

{
  "data": { ... }
  "extensions": {
    "runTime": 135
  }
}

Additional Validation Rules

GraphQL's validation phase checks the query to ensure that it can be sucessfully executed against the schema. The validationRules option allows for additional rules to be run during this phase. Rules are applied to each node in an AST representing the query using the Visitor pattern.

A validation rule is a function which returns a visitor for one or more node Types. Below is an example of a validation preventing the specific fieldname metadata from being queried. For more examples see the specifiedRules in the graphql-js package.

import { GraphQLError } from 'graphql';

export function DisallowMetadataQueries(context) {
  return {
    Field(node) {
      const fieldName = node.name.value;

      if (fieldName === "metadata") {
        context.reportError(
          new GraphQLError(
            `Validation: Requesting the field ${fieldName} is not allowed`,
          ),
        );
      }
    }
  };
}

Other Exports

getGraphQLParams(request: Request): Promise<GraphQLParams>

Given an HTTP Request, this returns a Promise for the parameters relevant to running a GraphQL request. This function is used internally to handle the incoming request, you may use it directly for building other similar services.

const graphqlHTTP = require('express-graphql');

graphqlHTTP.getGraphQLParams(request).then(params => {
  // do something...
})

Debugging Tips

During development, it's useful to get more information from errors, such as stack traces. Providing a function to formatError enables this:

formatError: error => ({
  message: error.message,
  locations: error.locations,
  stack: error.stack,
  path: error.path
})