A deep-dive into Relay, the friendly & opinionated GraphQL client

Relay is a JavaScript framework for declaratively fetching and managing GraphQL data. It enforces strict conventions to prevent developer errors and ensure performance as the app grows in size and complexity. The three main libraries of Relay are the Relay compiler, which analyzes any GraphQL inside your code during build time; the Relay runtime, a core runtime that is React-agnostic; and the React/Relay integration layer. Relay's key features include colocation, where data definitions and view definitions live together in each component, and fragments, which help write DRY queries. It also supports persisted queries for improved security and performance. The root query can be fetched using either the useLazyLoadQuery or usePreloadedQuery hooks, with the latter allowing more proactive data fetching. Relay requires a GraphQL server to follow its specifications, including providing a mechanism for refetching objects, describing how to page through connections, and structuring mutations to make them predictable.