Managing Resolver Context

Every GraphQL Resolver has a context argument. The graphql-mocks framework manages this context object and provides various entry points to include additional properties on the context object.

1. Initital Context
2. Query Context
3. Resolver Wrapper Context
4. Framework Managed Context

All of these contexts are flattened into a single context object available within a Resolver:

function resolver(parent, args, context, info) {
  // the context object is available as the third argument in a resolver
}

Initial Context

The optional initial context object is used as the base context, and is passed into the constructor of GraphQLHandler:

const handler = new GraphQLHandler({
  initialContext: {
    /*
      provides the base for all context objects
    */
  }
});

Query Context

An additional context object can be included on a per-query basis on the third argument of query method of the GraphQLHandler instance.

const additionalContext = {};
await handler.query(query, variables, additonalContext);

Resolver Wrapper Context

A Resolver Wrapper can return a new "outer" resolver that wraps the initial resolver. The "outer" resolver is a resolver function and therefore has access to the same context argument where it can be modified.

import { createWrapper, WrapperFor } from 'graphql-mocks/resolver';

const wrapper = createWrapper('my-wrapper', WrapperFor.FIELD, function resolverWrapper(originalResolver, wrapperOptions) {
  return async function outerResolver(parent, args, context, info) {

    // access to the `context` object here can be modified
    // and conditionally changed what is passed to the
    // `originalResolver`

    return await originalResolver(parent, args, context, info);
  };
});

Learn more with Introducing Resolver Wrappers and Creating Custom Wrappers.

Framework Managed Context

The graphql-mocks framework manages the context available in Resolvers to include additional helpful references to dependencies and current network requests and responses.

Dependencies

Dependencies added to a GraphQLHandler can be accessed within a Resolver Wrapper via the extractDependencies function.

function resolver(parent, args, context, info) {
  const { paper, anotherDependency } = extractDependencies(context, ['paper', 'anotherDependency']);
}

Network Requests and Responses

Most Network Handlers will include the request and/or response, and other useful context within the resolver context argument. These can be destrutured from the context object and are documented for each network handler.

For example the Mock Service Worker (msw) Network Handler includes the msw property with access to the request and response.

function resolver(parent, args, context, info) {
  const { msw } = context;
  // request and response from the `msw` request handler
  const { req, res } = msw;
}