How GraphQL Works — GraphQL in Production

GraphQL is a query language and runtime: the server publishes a strongly typed schema; clients send operations (queries, mutations, subscriptions) selecting exactly the fields they need; the server validates the operation against the schema and executes resolvers field by field. Everything usually goes through one endpoint (/graphql). The GraphQL over HTTP specification standardizes transport: GET for queries (cacheable), POST for any operation, and the application/graphql-response+json media type with meaningful HTTP status codes.

REST vs GraphQL at a glance

Criterion	REST	GraphQL
Endpoints	Many resource URLs	Usually one /graphql
Response shape	Server-defined	Client-selected fields
Over/under-fetching	Common; mitigated with fields/expand	Minimal by design
HTTP caching	Natural (GET URLs)	Needs persisted GET queries
Typing / introspection	Via OpenAPI	Built-in schema + introspection
Error model	HTTP status + problem JSON	errors[] array, partial data
Server complexity	Lower	Higher (resolvers, cost limits, N+1)

# Operation sent by a client
query OrderPage($id: ID!) {
  order(id: $id) {
    id
    status
    total { amount currency }
    items { quantity product { name imageUrl } }
  }
}
# Response
# { "data": { "order": { "id": "ord_1", "status": "PAID", ... } } }

Common pitfalls

Treating GraphQL as a thin layer over database tables.
Ignoring HTTP semantics entirely (everything POST, always 200).
Exposing an untested, unlimited schema publicly.

Key points

Typed schema + client-selected fields
Resolvers execute per field
Follow the GraphQL-over-HTTP spec

Further reading: GraphQL over HTTP specification

Practice questions

Why can GraphQL responses be harder to cache with HTTP caches?

Answer

Operations are often sent via POST to a single URL, so caches can't key on the URL; persisted queries sent via GET restore cacheability.

What does a resolver do?

Answer

It returns the value for one field of one type, given its parent object, arguments and request context; the executor calls resolvers for every selected field.