dabydat/alpha-omega/nestjs-cqrs-queries

NestJS CQRS Queries

Queries are read operations in CQRS. They don't modify state; they return data. Unlike commands, queries are side-effect free and can be optimized separately from writes.

Production patterns for: Query handlers, pagination, read optimization, parallel data fetching

Agent collaboration: Backend Dev (no side effects, return DTOs), DBA (index design, query optimization)

Core Principle: Queries Don't Change State

See references/why-queries.md for the commands-vs-queries rule, the ❌ BAD same-model example, and the ✅ GOOD separate read/write example.

Query Definition

See references/query-definition.md for GetEntityByIdQuery and GetEntitiesPaginatedQuery.

Query Response DTOs

See references/response-dtos.md for the three response types (simple, detail, paginated).

Search and Count Query

See references/search-count-query.md for the SearchEntitiesHandler and CountEntitiesHandler.

Module Registration

See references/module-registration.md for the QueryHandlers array and EntityModule.

Anti-Patterns to Avoid

See references/anti-patterns.md for the three ❌ examples (domain model return, business logic in query, no pagination).

Summary: Query vs Command

Golden rule: Queries are side-effect free. They read data and return DTOs. Any modification should be a command.

Related Skills

• nestjs-cqrs-commands - Command patterns and write operations
• nestjs-repository-pattern - Data access and query optimization
• nestjs-ddd-patterns - Domain-driven design with CQRS