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Managing Resolvers with Middlewares

Adding and Managing Resolvers on a Resolver Map is a common task when setting up different scenarios. This library provides two Resolver Map Middleware functions to make this easy, embed and layer, both which can apply Resolver Wrappers.

Using layer and embed with GraphQLHandler​

The generated Resolver Map Middleware from embed or layer create Resolver Map Middlewares that most often used with GraphQLHandler and its middlewares option.

const embeddedMiddleware = embed(/*...*/);
const layeredMiddleware = layer(/*...*/);

const handler = new GraphQLHandler({
  resolverMap,
  middlewares: [embeddedMiddleware, layeredMiddleware],
});

Using embed​

embed is commonly used to:

  • Target specific parts of the Resolver Map with Highlight
  • Add a Resolver with or without Resolver Wrappers
  • Target existing Resolvers already on the Resolver Map with Resolver Wrappers

Add Resolver​

Adds a resolver on the users field on the Query type, using a highlight callback that provides a highlight instance. See the available highlighters for more options on targeting the schema.

const middleware = embed({
  resolver: resolverToEmbed,
  highlight: (h) => h.include(field(['Query', 'users'])),
});

Add Resolver with a Resolver Wrapper​

Wrappers can be applied to the resolver being embedded, also. This example passes fooWrapper in an array of wrappers that are applied in order by the wrappers option on `embed.

const middleware = embed({
  resolver: resolverToEmbed,
  highlight: (h) => h.include(field(['Query', 'users'])),
  wrappers: [fooWrapper]
});

Add Resolver Replacing Existing​

Pass true for the replace option to replace any existing resolvers that might exist on the Resolver Map.

const middleware = embed({
  resolver: resolverToEmbed,
  replace: true,
});

Wrap Existing Resolvers with Resolver Wrappers​

By not specifying a resolver, the highlight option will be used to select existing Resolvers and apply the the Resolver Wrappers passed into the wrappers option.

const middleware = embed({
  highlight: (h) => h.include(field(['Query', 'users'])),
  wrappers: [fooWrapper]
});

Using layer​

Take fragments, or Resolver Map partials, and layer one or more lazily into a Resolver Map with the generated Resolver Map Middleware. These Resolver Map Partials can be defined separately and combined as needed with layer.

Adding Resolve Map Partials​

const queryPersonPartial = {
  Query: {
    person: queryPersonResolver
  },
};

const mutationAddPersonPartial = {
  Mutation: {
    addPerson: mutationAddPersonResolver
  }
}

const middleware = layer([queryPersonPartial, mutationAddPersonPartial]);

The resulting middleware in this example would lazily apply the queryPersonPartial, then the mutationAddPersonPartial via the generated Resolver Map Middleware.

Adding Resolvers with Resolver Wrappers​

Additionally, the Resolvers that are being layered in can also be wrapped with Resolver Wrappers by passing a wrappers option on the second argument to layer.

const middleware = layer(
  [resolverMapPartial],
  { wrappers: [fooWrapper, barWrapper] },
);

Replace Existing Resolvers​

As a safeguard, by default, resolver being added by layer won't replace existing resolvers unless the replace true option is provided.

const middleware = layer(
  [resolverMapPartial],
  { replace: true },
);