graphql-component

GraphQL schema components.

This project is designed to make npm module or component based development of graphql schemas easy.

Read more about the idea here.

graphql-component lets you built a schema progressively through a tree of graphql schema dependencies.

Repository structure

• lib - the graphql-component code.
• test/examples/example-listing/property-component - a component implementation for Property.
• test/examples/example-listing/reviews-component - a component implementation for Reviews.
• test/examples/example-listing/listing-component - a component implementation composing Property and Reviews.
• test/examples/example-listing/server - the "application".

Running the example

Can be run with node examples/server/index.js or npm start which will start with debug flags.

Debugging

Enable debug logging with DEBUG=graphql-component:*

Activating mocks

To intercept resolvers with mocks execute this app with GRAPHQL_DEBUG=1 enabled.

API

• GraphQLComponent(options) - the component class, which may also be extended. Its options include:
  • types - a string or array of strings representing typeDefs and rootTypes.
  • resolvers - an object containing resolver functions.
  • imports - an optional array of imported components for the schema to be merged with.
  • context - an optional object { namespace, factory } for contributing to context.
  • directives - an optional object containing custom schema directives.
  • useMocks - enable mocks.
  • preserveMockResolvers - preserve type resolvers in mock mode.
  • mocks - an optional object containing mock types.
  • dataSources - an array of data sources instances to make available on context.dataSources .
  • dataSourceOverrides - overrides for data sources in the component tree.

A new GraphQLComponent instance has the following API:

• schema - getter that returns an executable schema representing the entire component tree.
• context - context function that build context for all components in the tree.
• schemaDirectives - schema directives for the entire component tree.
• execute - accepts a graphql query to execute agains schema.
• types - this component's types.
• resolvers - this component's resolvers.
• imports - this component's imported components.
• mocks - custom mocks for this component.
• directives - this component's directives.
• dataSources - this component's data source(s), if any.

General usage

Creating a component using the GraphQLComponent class:

const GraphQLComponent = require('graphql-component');

const { schema, context } = new GraphQLComponent({ types, resolvers });

Encapsulating state

Typically the best way to make a re-useable component with instance data will be to extend GraphQLComponent.

const GraphQLComponent = require('graphql-component');
const resolvers = require('./resolvers');
const types = require('./types');
const mocks = require('./mocks');

class PropertyComponent extends GraphQLComponent {
  constructor({ useMocks, preserveTypeResolvers }) {
    super({ types, resolvers, mocks, useMocks, preserveTypeResolvers });
  }
}

module.exports = PropertyComponent;

This will allow for configuration (in this example, useMocks and preserveTypeResolvers) as well as instance data per component (such as data base clients, etc).

Aggregation

Example to merge multiple components:

const { schema, context } = new GraphQLComponent({
  imports: [
    new Property(),
    new Reviews()
  ]
});

const server = new ApolloServer({
  schema,
  context
});

Excluding root fields from imports

You can exclude root fields from imported components:

const { schema, context } = new GraphQLComponent({
  imports: [
    {
      component: new Property(),
      exclude: ['Mutation.*']
    },
    {
      component: new Reviews(),
      exclude: ['Mutation.*']
    }
  ]
});

This will keep from leaking unintended surface area. But you can still delegate calls to the component's schema to enable it from the API you do expose.

Data Source support

Data sources in graphql-component do not extend apollo-datasource's DataSource class.

Instead, data sources in components will be injected into the context, but wrapped in a proxy such that the global context will be injected as the first argument of any function implemented in a data source class.

This allows there to exist one instance of a data source for caching or other statefullness (like circuit breakers), while still ensuring that a data source will have the current context.

For example, a data source should be implemented like:

class PropertyDataSource {
  get name() {
    return 'PropertyDataSource';
  }
  async getPropertyById(context, id) {
    //do some work...
  }
}

This data source would be executed without passing the context manually:

const resolvers = {
  Query: {
    property(_, { id }, { dataSources }) {
      return dataSources.PropertyDataSource.getPropertyById(id);
    }
  }
}

Setting up a component to use a data source might look like:

new GraphQLComponent({
  //...
  dataSources: [new PropertyDataSource()]
})

Directly executing components

Components can be directly executed via the execute function. The execute function is basically a passthrough to graphql.execute and is mostly useful for components calling imported components and the like.

For example, this allows one component to invoke another component and still get the benefits of that component's schema type resolvers and validation.

execute(input, options) accepts an input string and an optional options object with the following fields:

• root - root object.
• context - context object value.
• variables - key:value mapping of variables for the input.

The execute function also adds some helper fragments. For any type you query in a component, a helper fragment will exist to query all fields.

Example extending Property to include a reviews field that delegates to another component:

class PropertyComponentReviews extends GraphQLComponent {
  constructor({ useMocks, preserveTypeResolvers }) {
    const propertyComponent = new PropertyComponent();
    const reviewsComponent = new ReviewsComponent();

    super ({
      types: [
        `type Property { reviews: [Review] }`
      ],
      resolvers: {
        Property: {
          reviews(_, args, context) {
            //TODO: error handle here of course!
            return reviewsComponent.execute(`query { reviewsByPropertyId(id: ${_.id}) { ...AllReview }}`, { context });
          }
        }
      },
      imports: [
        propertyComponent,
        {
          component: reviewsComponent,
          exclude: ['*'] //Exclude the imported component's API
        }
      ]
    });
  }
}

For the Review type in the reviewsComponent, a helper fragment will exist as AllReview that provides all fields.

Adding to context

Example context argument:

const context = {
  namespace: 'myNamespace',
  factory: function ({ req }) {
    return 'my value';
  }
};

After this, resolver context will contain { ..., myNamespace: 'my value' }.

Context middleware

It may be necessary to transform the context before invoking component context.

const { schema, context } = new GraphQLComponent({types, resolvers, context});

context.use('transformRawRequest', ({ request }) => {
  return { req: request.raw.req };
});

Using context now in apollo-server-hapi for example, will transform the context to one similar to default apollo-server.

Mocks

graphql-component accepts mocks in much the same way that Apollo does but with one difference.

Instead of accepting a mocks object, it accepts (importedMocks) => mocksObject argument. This allows components to utilize the mocks from other imported components easily.