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Using Middlewares

The GraphQLHandler accepts an array of middlewares, chaining together a series of modifications to the Resolver Map (or an empty object if one does not exist). After all the Middlewares have been run the GraphQLHandler takes the final "packed" Resolver Map and applies each Resolver function to the GraphQLSchema, its types and fields.

The specific internal mechanics of a middleware are explained in Introducing Resolver Map Middlewares and the following sections.

Adding Middlewares at Initialization​

The most common way of applying Resolver Map Middlewares is at initialization via the middlewares option on the GraphQLHandler constructor.

import { GraphQLHandler, embed } from 'graphql-mocks';
import { middlewareA, middlewareB } from './middlewares';

const handler = new GraphQLHandler({
  middlewares: [middlewareA, middlewareB]
  dependencies: { graphqlSchema }
});

Adding Middlewares via applyMiddlewares​

After initialization of the handler middlewares can be applied via the applyMiddlewares method.

import { GraphQLHandler, embed } from 'graphql-mocks';
import { middlewareA, middlewareB } from './middlewares';

const handler = new GraphQLHandler({
  dependencies: { graphqlSchema }
});

handler.applyMiddlewares([falsoMiddleware, loggingMiddleware], { reset: false });

Options​

The second argument to applyMiddlewares is an optional object of options.

reset​

  • Default: false

If true this option resets the middlewares used to those passed in on the first argument to applyMiddlewares. If false the middlewares are added to the end of the currently existing array of middlewares.