GraphQLとは

Wish an API gave you exactly what you asked for? GraphQL is a query language for APIs that lets clients request precisely the data they need.

REST endpoints return a fixed shape, so you hit over-fetching — asking for a user’s name but downloading their whole profile, wasting bandwidth.

The flip side is under-fetching: one endpoint isn’t enough, so you chain calls for users, then posts, then comments — many round trips that slow you down.

GraphQL solves both: clients ask for exactly the fields they need from a single endpoint, so you get fewer requests and leaner data transfer.

At the heart of every GraphQL API is its schema — the contract. It defines every type clients can query and how they relate, written in SDL.

Types are defined in SDL. Here a User has id, name, and email fields; the ! marks a field as non-nullable.

A query is how a client asks for data. It mirrors the shape you want, fetching only the fields you list — even from nested objects.

Here’s a simple query: ask only for id and name, and that’s all the server returns for the user with id 1. Nothing extra.

Why pick GraphQL? Efficient fetching, a strongly typed schema that prevents errors, painless API evolution, and great tooling like GraphiQL.

GraphQL shines with complex, interconnected data, multiple client platforms on one API, microservice gateways, and fast frontend iteration.

You’ve got the fundamentals: GraphQL kills over- and under-fetching, the schema is the contract, and queries request exactly what you want. Spring Boot next.