Default Variable Values

Default Variable Values Overview

At its core, default variable values is about doing one thing well inside your GraphQL project. Once you understand the pattern, you can apply it consistently across features and teams.

Good default variable values pays off across the whole codebase: fewer surprises, easier testing, and smoother onboarding. The snippet below is a solid starting point.

query GetUser($id: ID!) {
  user(id: $id) {
    id
    name
    posts(first: 10) {
      id
      title
    }
  }
}

Clients request exactly the fields they need, passing arguments through typed variables.

Default Variable Values Example

const typeDefs = gql`
  type Query { hello: String! }
`;
const resolvers = { Query: { hello: () => 'world' } };
const server = new ApolloServer({ typeDefs, resolvers });

• Start from a minimal Default Variable Values example and grow it only as needed.
• Keep configuration explicit so Default Variable Values behaves the same in every environment.
• Name things clearly so teammates understand your Default Variable Values at a glance.
• Add tests around Default Variable Values early to lock in expected behaviour.

GraphQL Cheatsheet

Quick GraphQL reference related to default variable values.

How Default Variable Values Works in GraphQL

Default Variable Values fits into GraphQL's model of a single typed schema that clients query for exactly the data they need. The server resolves each requested field through resolver functions.

Clients request exactly the fields they need, passing arguments through typed variables.

• The schema is the contract between client and server.
• Resolvers fetch data field by field, including nested types.
• Clients request only the fields they use, avoiding over-fetching.
• Context carries auth and shared services into every resolver.

Practical Guidance for Default Variable Values

In production, default variable values should be efficient and secure. Batch data access with DataLoader, guard resolvers with authorization, and limit query depth and complexity.

Common Mistakes

• Skipping error handling and edge cases when wiring up default variable values.
• Leaving default variable values untested, so regressions slip into production.
• Over-engineering default variable values before you actually need the extra flexibility.
• Ignoring documentation, which makes default variable values hard for the next developer to change.

Key Takeaways

• Default Variable Values is a core part of working effectively with GraphQL.
• Start small and keep default variable values focused on a single responsibility.
• Apply consistent patterns so default variable values scales across your project.
• Test and document default variable values to keep it maintainable over time.