CQRS (Command Query Responsibility Segregation)
Last Updated: February 3, 2026
In traditional application architecture, we use the same model for reading and writing data. The same entity class, the same database table, the same service methods handle both updates and queries. This works well for many applications, but it creates tension when read and write requirements diverge significantly.
CQRS (Command Query Responsibility Segregation) resolves this tension by separating the read and write sides of an application. Commands handle updates to the system. Queries handle reads. Each side can be optimized independently.
The pattern builds on the event-driven concepts we explored in the previous chapter. Events often serve as the bridge between the write side (which publishes events) and the read side (which consumes events to build query-optimized views).
In this chapter, you will learn:
- The core principle of separating commands and queries
- How CQRS differs from traditional CRUD architectures
- Implementation approaches from simple to fully separated
- The relationship between CQRS and event-driven architecture
- Trade-offs and when CQRS is appropriate
- Common patterns and best practices