This demo project demonstrates the use of Apollo's products to create GraphQL solutions. Apollo Federation is used to create a federated architecture instead of a monolithic graph.

This demo project only serves as an example and does not provide a step-by-step guide on recreating such applications using tools like Rover Cli.

Here are some useful resources where you can learn about all Apollo Products and GraphQL concepts:

• Official Apollo documentation: https://www.apollographql.com/docs/
• Apollo Federation documentation: https://apollo-gateway-0-28-3--apollo-federation-docs.netlify.app/docs/federation/quickstart/
• Apollo Odyssey tutorials (video + text): https://www.apollographql.com/tutorials/
• A list of Third Party libraries that support Apollo Federation: https://apollo-gateway-0-28-3--apollo-federation-docs.netlify.app/docs/federation/other-servers/

                        Book1 API
                       /
           Book API - <
          /            \
Router - <              Book2 API
          \
           Author API - Author REST 
                        Data Source

Router: the entry point for all requests (via Apollo Router)

• routes the request to the corresponding APIs/subgraphs
• does the stitching

Book API: the unified API for all book APIs (via Apollo Server)

• sends requests to Book1 and Book2 APIs
• its schema is the union of the Book1 and Book2 schemas (thus Book2), where those fields not in the intersection of the 2 schema definitions, are not required

Book1 APIs: has fields id, authorId, title, pages

Book2 APIs: has fields id, authorId, title, pages, hardcover

Author API: the API for the authors of all Book APIs' contents (both Book1 and Book2 APIs)

• fetches data from the Author REST API, which returns more fields, than what the Author GQL API needs

Author REST DS: returns data of authors as response of GET requests

• same functionality as the Author GQL API's, but fetches more fields