GraphQL Best Practices

Standards for designing and implementing GraphQL APIs.

1. Schema Design

• Business Logic Isolation: Do not write business logic inside resolvers. Resolvers should only extract arguments and pass them to dedicated service/domain layer functions.
• Nullability: Be mindful of non-null (!) fields. Only mark fields as non-null if you are absolutely certain they will never be missing, as a single null in a non-null field will bubble up and destroy the entire parent object.
• Custom Scalars: Use custom scalars (e.g., DateTime, Email) to enforce type constraints at the schema level instead of raw String.

2. Mutations

• Input Types: Use a single, required input object argument for mutations instead of passing many individual arguments.
• Payload Types: Return a specific payload type (e.g., UpdateUserPayload) that includes the mutated object and any potential operation-specific errors, rather than just returning the object.

3. Performance (N+1 Problem)

• DataLoader: ALWAYS use Facebook's dataloader pattern (or equivalent) to batch and cache database requests for nested relationships. Never loop and await queries inside child resolvers.
• Query Complexity: Implement query complexity limits or depth limits on your GraphQL server to prevent malicious or accidental resource exhaustion.

4. Error Handling

• Use the standard errors array for unexpected exceptions.
• For business logic errors (e.g., "Email already taken"), model them as Union types in your schema (e.g., union CreateUserResult = User | EmailAlreadyTakenError) so clients can handle them gracefully.