projection-patterns

Build read models and materialized views from event streams using projection patterns. Comprehensive guide to building projections and read models for event-sourced systems. - Covers four projection types: live (real-time subscriptions), catchup (historical processing), persistent (with checkpointing), and inline (strong consistency) - Includes five ready-to-use templates: basic projector framework, order summary projection, Elasticsearch search indexing, daily sales aggregation, and multi-table customer activity tracking - Emphasizes idempotency, transactional consistency, checkpoint management, and safe rebuilding strategies - Best practices section covers monitoring lag, error handling, event ordering, and denormalization patterns for query optimization - Building CQRS read models - Creating materialized views from events - Optimizing query performance - Implementing real-time dashboards - Building search indexes from events - Aggregating data across streams - Make projections idempotent - Safe to replay - Use transactions - For multi-table updates - Store checkpoints - Resume after failures - Monitor lag - Alert on projection delays - Plan for rebuilds - Design for reconstruction - Don't couple projections - Each is independent - Don't skip error handling - Log and alert on failures - Don't ignore ordering - Events must be processed in order - Don't over-normalize -...