Applications that are data–driven depend on remote queries that run through APIs. For years, web services have provided basic support for simple query structures. Those services, however, often constrained developers who needed more granular approaches that provided flexibility without creating a huge collection of unnecessary calls. GraphQL a query language for APIs that was originally built by Facebook allows developers to choose the kinds of requests they want to make, and receive information on multiple facets of that query in one request. The GraphQL approach to querying across networks can address a wide variety of large–scale development problems. GraphQL enables you to nest multiple request in one query.
Specification: GraphQL: Introduction to GraphQL for beginners