Node.js › GraphQL with Node.js

How would you set up a basic GraphQL server in Node.js using Apollo Server, and what are schema and resolvers?

Beginner

Answer

A GraphQL server needs a schema (written in GraphQL's Schema Definition Language, describing the available types and operations) and resolvers (functions that actually fetch or compute the data for each field defined in the schema) -- Apollo Server ties these together and handles the HTTP layer, parsing incoming GraphQL queries and invoking the appropriate resolver functions to build the response.

const { ApolloServer, gql } = require('apollo-server');

const typeDefs = gql`
  type User { id: ID!, name: String!, email: String! }
  type Query { user(id: ID!): User }
`;

const resolvers = {
  Query: {
    user: async (_, { id }) => db.users.findById(id),
  },
};

const server = new ApolloServer({ typeDefs, resolvers });
server.listen().then(({ url }) => console.log(`Server ready at ${url}`));

Real-world example A team building a new API for a mobile app chooses GraphQL specifically so the mobile client can request exactly the fields it needs for each screen (like only 'name' and 'avatarUrl' for a list view) in a single request, rather than either over-fetching a full REST resource or needing several separate REST endpoint calls.

Common follow-ups: How does a GraphQL query's shape directly determine which resolvers get called and in what order?;What's the difference between the Query, Mutation, and Subscription root types in a GraphQL schema?

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