Mutations & Updates Interview Questions

Mutations implemented using useMutation hook. Configure variables, options, cache updates. Features: optimistic updates, error handling. Common pattern: mutation function returns promise with result.

Optimistic updates provide immediate UI feedback before server response. Implement through optimisticResponse option. Features: temporary cache updates, automatic rollback on error. Improves perceived performance.

Cache updates through update function, refetchQueries. Implement cache modifications, field updates. Features: automatic cache normalization, manual cache writes. Ensures cache consistency.

RefetchQueries updates queries after mutation. Specify queries to refetch, variables. Features: automatic query updates, cache refresh. Ensures data consistency across components.

Error handling through onError callback, error policies. Implement error messages, recovery logic. Features: error tracking, user feedback. Handles network errors, GraphQL errors.

Mutation variables pass dynamic data to mutations. Configure through options object, typed variables. Features: type safety, dynamic values. Handles user input, dynamic data.

Concurrent mutations through mutation queue, synchronization. Implement ordering, dependency handling. Features: race condition prevention, sequence control. Maintains data consistency.

Update function modifies cache after mutation. Access cache directly, perform updates. Features: manual cache writes, complex updates. Handles custom cache modifications.

Batch mutations combine multiple operations. Implement through Apollo Link batch. Features: request batching, optimization. Reduces network requests, improves performance.

Loading states track mutation progress. Access through mutation result object. Features: loading indicator, disabled states. Handles user feedback, UI updates.

Rollbacks through error handling, cache restoration. Implement recovery logic, state management. Features: automatic rollback, manual recovery. Handles failed mutations.

Mutation hooks provide declarative mutation handling. Access mutation function, result data. Features: React integration, type safety. Simplifies mutation implementation.

File uploads through Apollo Upload Client. Handle multipart form data, progress. Features: file handling, upload tracking. Supports single/multiple file uploads.

Mutation options configure behavior. Include variables, update function, optimistic response. Features: error policies, refetch queries. Controls mutation execution.

Dependent mutations through chaining, async/await. Implement sequence control, error handling. Features: mutation ordering, data dependencies. Manages related mutations.

Result types define mutation responses. Include data, loading state, error information. Features: type safety, result handling. Structures mutation responses.

Offline mutations through queue system, persistence. Implement retry logic, conflict resolution. Features: offline support, sync handling. Handles network interruptions.

Completion handling through onCompleted callback. Implement success actions, notifications. Features: result processing, UI updates. Handles successful mutations.

Side effects through update function, callbacks. Implement additional actions, state updates. Features: cache modifications, external updates. Manages mutation impacts.

Mutation policies control execution behavior. Configure error handling, cache updates. Features: retry policies, update strategies. Defines mutation behavior.

Mutation testing through mock providers, test utilities. Implement assertions, response mocking. Features: result verification, error testing. Ensures mutation reliability.

Mutation fragments define reusable mutation parts. Share common fields, type definitions. Features: code reuse, maintainability. Reduces duplicate mutation code.

Conflict handling through version checks, merge strategies. Implement conflict resolution, retry logic. Features: data consistency, user feedback. Manages concurrent updates.

Mutation directives modify mutation behavior. Configure execution, caching. Features: custom directives, behavior control. Extends mutation capabilities.

Rate limiting through Apollo Link, request throttling. Implement request control, queue management. Features: request limits, timing control. Prevents server overload.

Best practices include proper error handling, optimistic updates, cache management. Implement type safety, testing. Features: performance optimization, reliability. Ensures robust mutations.

Authorization through context, headers. Implement access control, token handling. Features: permission checks, secure mutations. Ensures authorized access.

Composition combines multiple mutations. Implement reusable parts, shared logic. Features: code organization, maintainability. Structures complex mutations.

Monitoring through Apollo Studio, custom tracking. Implement performance metrics, error logging. Features: analytics, debugging. Tracks mutation behavior.