GraphQL HTTP Server Middleware

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

Installation

npm install --save express-graphql

Then 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);

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.
context: A value to pass as the context to the graphql() function from GraphQL.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.

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
  }
}

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
})

ngocdiep/express-graphql