Overview
CRUD (Create, Read, Update, Delete) models an application around a single data model that handles both reads and writes through uniform operations. CQRS (Command Query Responsibility Segregation) instead splits reads and writes into separate paths, often with different models and stores optimized for each. The choice matters most as a system’s read/write patterns diverge or its business logic grows too complex for a single model to represent cleanly.
Comparison Diagram
Comparison Table
| Aspect | CRUD | CQRS |
|---|---|---|
| Request handling | Single endpoint set (GET/POST/PUT/DELETE) hits one code path for both reads and writes | Requests split into distinct Command (write) and Query (read) channels with separate handlers |
| Data model | One model represents the entity for both reading and writing | Separate write model (domain/aggregate) and read model (denormalized view) per side |
| Storage | Single database or table serves both reads and writes | Optional separate stores per side, e.g. relational for writes, cache or search index for reads |
| Consistency | Strongly consistent by default since reads hit the same store just written to | Read side is often eventually consistent, synced from the write side via events |
| Business logic placement | Validation and rules scattered across create/update handlers | Rules concentrated in command handlers that enforce invariants before state changes |
| Scaling | Read and write load scale together since they share the same path | Read and write sides can be scaled and optimized independently |
| Implementation overhead | Minimal; straightforward to build, test, and reason about | Higher; requires sync mechanism and handling of eventual consistency |
Key Differences
- CRUD uses a unified model for reads and writes; CQRS separates commands and queries into distinct paths
- CRUD read-after-write is immediate since storage is shared; CQRS’s read side is often eventually consistent
- CRUD business logic lives in generic handlers; CQRS pushes rules into explicit command handlers
- CQRS allows independent scaling of reads and writes; CRUD scales both together
- CRUD is simpler to build; CQRS trades that simplicity for flexibility at the cost of architectural complexity
When to Use Each
CRUD
- Simple domain or admin tools: Internal tools and basic CRUD apps where reads and writes are equally simple don’t need separate models.
- Small team or MVP: A single model is faster to build, test, and onboard new engineers to.
- Uniform read/write load: When traffic patterns for reads and writes are similar, there’s no scaling benefit to splitting them.
CQRS
- High read/write asymmetry: Dashboards or reporting views with heavy reads but infrequent writes benefit from a read model optimized separately.
- Complex domain logic: Rich business rules and invariants are easier to enforce through explicit command handlers than generic update endpoints.
- Event sourcing systems: CQRS pairs naturally with event sourcing, giving a clear audit trail of every state change.
- Independent scaling needs: Read replicas or caches can be scaled and tuned separately from the write database.