Extend GraphQL API

Introduction

When it comes to HTTP API development, Webiny relies on GraphQL . In fact, all of the applications that are part of the Webiny Serverless CMS, for example Page Builder or Headless CMS , are using it in order to enable developers programmatic interaction via a client of their choice, for example a browser.

By default, every Webiny project starts off with two separate GraphQL APIs.

Default GraphQL API

The default GraphQL API (or just GraphQL API) is the GraphQL API that’s located within the api/code/graphql folder. All of the Webiny Serverless CMS applications are built on top of it, and, in the same fashion, the API can be extended by developers, if need be.

Headless CMS GraphQL API

The Headless CMS GraphQL API is a special standalone GraphQL API that is introduced by the Headless CMS application. It’s located in the api/code/headlessCMS folder and, like the default GraphQL API, can also be extended by developers.

Extending GraphQL API

In general, when talking about extending an existing GraphQL API, we’re usually referring to one or more of the following:

• adding new query or mutation GraphQL operations
• adding new GraphQL types
• extending existing GraphQL types with additional fields

For example, we might want to add a new, Page Builder-related, duplicatePage mutation, that would be responsible for making copies of provided pages. Or, we might just want to add an extra field to the PbPage GraphQL type, so that we can store some additional data for each page.

And although, depending on the application and the change we want to perform, some of the steps in the overall GraphQL extension process may differ, in all cases, we will want to start by registering a new GraphQLSchemaPlugin plugin.

The plugin is registered within your GraphQL API’s application code. For example, if we wanted to extend the default GraphQL API, we would create the plugin inside of the api/code/graphql/src/plugins folder, and register it in the api/code/graphql/src/index.ts entrypoint file. On the other hand, if we wanted to extend the Headless CMS GraphQL API, we would create the plugin inside of the api/code/headlessCMS/src/plugins folder, and register it in the api/code/headlessCMS/src/plugins/index.ts entrypoint file.

The following is an example of a simple GraphQLSchemaPlugin plugin that extends the default GraphQL API with a new listBooks query.

import { GraphQLSchemaPlugin } from "@webiny/handler-graphql/plugins";

// Make sure to import the `Context` interface and pass it to the `GraphQLSchemaPlugin`
// plugin. Apart from making your application code type-safe, it will also make the
// interaction with the `context` object significantly easier.
import { Context } from "~/types";

export default new GraphQLSchemaPlugin<Context>({
  // Extend the `Query` type with the `Book` type and `listBooks` query field,
  // which returns a list of all books previously saved in the database.
  typeDefs: /* GraphQL */ `
    type Book {
      title: String
      description: String
    }
    extend type Query {
      # Returns a list of all users
      listBooks: [Book]
    }
  `,
  // In order for the `listBooks` to work, we also need to create a resolver function.
  resolvers: {
    Query: {
      listBooks: async (_, args, context) => {
        // In a real life application, these would be loaded from the database.
        const books = [
          { title: "First book", description: "This is the first book." },
          { title: "Second book", description: "This is the second book." }
        ];

        // Finally, return the list of books using the `ListResponse` class instance.
        return books;
      }
    }
  }
});

the plugin

api/code/graphql/src/index.ts

{
  listBooks {
    title
    description
  }
}

Executing the query should give us the following result:

Executing the new listBooks Query via API Playground

(click to enlarge)

Additional Related Examples

For more concrete examples, you can also visit the following guides which explain how to extend GraphQL types and operations that belong to different Webiny applications:

• Page Builder
• Headless CMS