Software Engineering Radio - the podcast for professional software developers Episode 218: Udi Dahan on CQRS (Command Query Responsibility Segregation)
4 snips
Jan 30, 2015 
In this engaging discussion, Udi Dahan, a pioneer in service-oriented architecture and co-originator of the CQRS pattern, dives into the nuances of Command Query Responsibility Segregation. He explains how separating read and write models can simplify complex domains, and outlines the benefits of event sourcing for preserving object state. Udi also touches on vital infrastructure choices and emphasizes the importance of collaborating with domain experts to select the right architectural patterns for specific needs.
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Separate Models For Reads And Writes
- Using different objects for reads and writes prevents pulling models in two directions and reduces complexity.
- Udi Dahan and Greg Young independently found this separation improved maintainability and named it CQRS.
Commands Need Freshness, Queries Can Be Stale
- Queries and commands have different correctness and staleness needs, so they pull models in different directions.
- CQRS applies single-responsibility by splitting command logic (strong consistency) from query logic (tolerant of staleness).
Design Persistence To Match Responsibilities
- Evaluate separate persistent models for queries and commands only when complexity justifies it.
- Design query data structures explicitly if you want clean, highly optimized command and query layers.
