The Command Query Responsibility Segregation (CQRS) pattern is a design pattern used in software engineering to separate the responsibilities of handling commands (changing state) from the responsibility of querying data. This pattern splits the responsibility of handling commands that change data from handling queries that retrieve data in software systems¹².

Key Principles

In traditional architectures, the same data model is used to query and update a database. This approach can become unwieldy in complex applications due to the asymmetrical nature of read and write workloads. CQRS addresses this by separating reads and writes into different models, using commands to update data and queries to read data¹.

Commands should be task-based rather than data-centric. For example, instead of setting a reservation status to reserved, a command should be "Book hotel room." This approach may require changes to the user interaction style and business logic¹.

Implementation