GraphQL Express Middleware

Create a GraphQL HTTP server with Express.

npm install --save express-graphql

Install express-graphql as middleware in your express server:

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

var app = express();

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

Options

The graphqlHTTP function accepts the following options:

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

• context: A value to pass as the context to the graphql() function from graphql-js.

• rootValue: A value to pass as the rootValue to the graphql() function from graphql-js.

• 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.

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

• graphiql: If true, may present GraphiQL when loaded directly from a browser (a useful tool for debugging and exploration).

Debugging

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
})

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, graphql-express 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.

Advanced Options

In order to support advanced scenarios such as installing a GraphQL server on a dynamic endpoint or accessing the current authentication information, express-graphql allows options to be provided as a function of each express request, and that function may return either an options object, or a Promise for an options object.

This example uses express-session to provide GraphQL with the currently logged-in session as the context of the query execution.

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

var app = express();

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

app.use('/graphql', graphqlHTTP(request => ({
  schema: MySessionAwareGraphQLSchema,
  context: request.session,
  graphiql: true
})));

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

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