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How do GraphQL Mutations differ from Queries, and how would you define one to create a new resource?

Intermediate

Answer

Queries are for reading data and are expected to have no side effects, while Mutations are explicitly for operations that change server-side state (creating, updating, or deleting data) -- syntactically similar to queries but declared under the schema's Mutation type, with the convention that mutations are executed sequentially (one at a time) when multiple are included in a single request, unlike queries which can be resolved in parallel.

const typeDefs = gql`
  type Mutation { createUser(name: String!, email: String!): User! }
`;

const resolvers = {
  Mutation: {
    createUser: async (_, { name, email }) => {
      return db.users.create({ name, email });
    },
  },
};

// Client sends: mutation { createUser(name: "Alice", email: "alice@example.com") { id name } }

Real-world example A social media application defines a 'createPost' mutation that validates the input, saves the new post to the database, and returns the created post's fields the client requested, following GraphQL's convention of separating this state-changing operation clearly from the app's read-only query operations.

Common follow-ups: Why does GraphQL execute multiple mutations in a single request sequentially rather than in parallel like queries?;How do you handle partial failure when a mutation succeeds in modifying data but a subsequent part of the resolver fails?

Error Handling;Architecture & Design Patterns