GraphQL is a query language for APIs and a runtime for executing those queries, developed by Facebook in 2012 and open-sourced in 2015. Unlike REST APIs that expose fixed endpoints, GraphQL allows clients to request exactly the data they need in a single request. It has three operation types: query (read), mutation (write), and subscription (real-time updates).

Frequently Asked Questions

query is for read-only operations — fetching data. mutation is for write operations — creating, updating, or deleting data. While both technically return data, the semantic distinction matters: queries can be cached and run in parallel, while mutations are executed serially and cannot be cached.

The exclamation mark means "non-null" — the field is guaranteed to never return null. String! is a non-nullable string; [String!]! is a non-nullable list of non-nullable strings. Without !, null is a valid return value, and clients must handle it.

A fragment is a reusable piece of a GraphQL query. It lets you define a set of fields once and include them in multiple queries, reducing duplication. Fragments always reference a specific type: fragment UserFields on User { id name email }. They're especially useful for sharing field selections between different queries in client-side code.

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