Nestjs Search

Search Engine & Full-Text

Priority: P1 (OPERATIONAL)

• Pattern: CQRS (Command Query Responsibility Segregation).
• Write: To Primary Database (Postgres/MySQL). Source of Truth.
• Read (Complex): To Search Engine (Elasticsearch, OpenSearch, MeiliSearch). Optimized for filtering, fuzzy search, and aggregation.

Synchronization ( Hard Part)

• Dual Write (Anti-Pattern): await db.save(); await es.index();.
• Why: Partial failures leave data inconsistent. Slows down HTTP response.
• Event-Driven (Recommended):

1. Service writes to DB.
2. Service emits EntityUpdated.
3. Event Handler (Async) pushes to Queue (BullMQ).
4. Worker indexes document to Search Engine with retries.

• CDC (Golden Standard): Change Data Capture (Debezium). Connects directly to DB transaction log. No app conceptual overhead, but higher ops complexity.

Organization

• Module: Encapsulate client in SearchModule.
• Abstraction: Create generic SearchService<T> helpers.
• indexDocument(id, body)
• search(query, filters)
• Mapping: Use class-transformer to map Entities to "Search Documents". Keep docs flatter than relational entities.

Testing

• E2E: not mock search engine in critical E2E flows.
• Docker: Spin up elasticsearch:8 container in test harness to verify indexing works.

Anti-Patterns

• No dual writes to DB + ES: Use event-driven or CDC pattern; dual writes risk partial failure inconsistency.
• No Elasticsearch for structured queries: Use DB indexes for filtering; ES for full-text and complex search.
• No ES mocks in E2E search tests: Spin up elasticsearch:8 container to verify indexing behavior accurately.