Data fetching through useQuery hook (React), query components. Supports variables, polling, skip/fetchMore. Handles loading/error states automatically. Features automatic caching, real-time updates.
Pagination through fetchMore function, field policies. Supports offset/cursor-based pagination. Features: automatic cache merging, custom merge functions. Handles loading states automatically.
Reactive Variables store local state outside cache. Update components automatically on change. Features: no query requirement, direct reads/writes. Useful for global UI state.
Optimistic UI updates cache before server response. Improves perceived performance, user experience. Features: optimistic response object, error rollback. Used with mutations for instant feedback.
Error handling through error policies, custom error handling. Implement retry logic, user feedback. Features: error components, global error handling. Consider different error types.
FetchPolicy controls cache/network behavior. Options: cache-first, network-only, etc. Features: customizable per query, default policies. Balances performance and data freshness.
Code splitting through dynamic imports, lazy components. Supports query splitting, fragment colocation. Features: automatic chunk loading, performance optimization. Important for large applications.
Client-side operations through local state, field policies. Implement search logic, filtering functions. Features: reactive variables, local resolvers. Consider performance implications.
Client directive marks fields for local-only operations. Enables client-side resolvers, computed fields. Features: local state management, schema extension. Used for UI state, computed data.
Apollo Client is a comprehensive state management library for GraphQL. Key features: declarative data fetching, zero-config caching, predictable mutations, automatic query deduplication. Integrates with any GraphQL API and UI framework.
Local state management through field policies, reactive variables. Can extend schema with @client directive. Features: local resolvers, cache manipulation. Integrates with global cache management.
Authentication through HTTP headers, context. Configure ApolloLink for token management. Features: token refresh, error handling. Supports different auth strategies.
Fragments define reusable field sets. Promote code reuse, maintainability. Features: colocated queries, type safety. Used for component-specific data requirements.
Apollo Link customizes network layer behavior. Chain of middleware for request/response modification. Features: error handling, authentication, logging. Enables advanced network customization.
Error handling through GraphQL errors, network errors. Provides error information in query/mutation results. Features: error policies, retry mechanisms. Supports custom error handling logic.
Offline support through cache persistence, local state. Implement retry strategies, queue mutations. Features: cache storage, conflict resolution. Consider offline-first architecture.
SSR through getDataFromTree, cache extraction. Handle initial state, hydration. Features: automatic cache population, state transfer. Consider SEO, performance requirements.
Initialize using ApolloClient constructor, configure with cache and link options. Wrap application with ApolloProvider. Example: new ApolloClient({ cache: new InMemoryCache(), uri: 'graphql-endpoint' }). Set default options for queries/mutations.
InMemoryCache is Apollo's normalized caching system. Stores query results, handles data normalization. Features: type policies, field policies, custom resolvers. Essential for performance, offline capabilities, data consistency.
Queries for reading data (idempotent), Mutations for modifying data. Queries can run parallel, mutations execute sequentially. Queries automatically cached, mutations require cache updates. Different hooks: useQuery vs useMutation.
TypePolicies configure cache behavior per type. Define key fields, field merging strategies. Features: custom merge functions, field policies. Essential for cache normalization.
Real-time updates through subscriptions, polling. WebSocket integration for live data. Features: subscription components/hooks, automatic updates. Supports optimistic UI updates.
useQuery hook fetches and manages query data. Provides loading/error states, refetch functions. Features: automatic caching, skip/pollInterval options. Essential for React component data fetching.
Cache normalization through unique identifiers, type policies. Prevents data duplication, ensures consistency. Features: custom key fields, merge functions. Essential for efficient caching.
Cache redirects customize cache reading behavior. Define relationships between cached entities. Features: field policies, custom resolvers. Useful for complex data relationships.
File uploads through apollo-upload-client package. Supports multipart form data, progress tracking. Features: multiple file uploads, abort capability. Requires server-side configuration.
Field policies customize field behavior in cache. Define read/write functions, merge strategies. Features: custom field handling, computed fields. Essential for complex cache management.
