Presentation prepared by Rafal Machnik presented on Quality Questions Conference.

1. CQRS
CQRS as a performance and security booster

3. What is CQRS?

5. When CQRS is not suitable?
● Where the domain or the business rules are simple.
● Where a simple CRUD-style user interface and the related data access operations
are sufficient.
● For implementation across the whole system. There are specific components of an
overall data management scenario where CQRS can be useful, but it can add
considerable and often unnecessary complexity where it is not actually required.

6. When CQRS?
● Collaborative domains where multiple operations are performed in parallel on the
same data.
● Use with task-based user interfaces (where users are guided through a complex
process as a series of steps), with complex domain models.
● Scenarios where performance of data reads must be fine-tuned separately from
performance of data writes, especially when the read/write ratio is very high, and
when horizontal scaling is required.

7. CQRS vs performance
● Reading operations are separated from writing operations
● Possible different models for reading and writing

8. CQRS vs security
● Responsibility segregation brings more space for security
● More flexibility for reading and writing security rules
● “Asking question shouldn't change the answer”

9. Related concepts
● Reactive apps
● Task based UI
● Event sourcing
● Eventual consistency
● Example: Reporting app

10. CQRS and event sourcing

11. How to test CQRS and event sourcing?
AAA
● Arrange - when you set up initial state for a test,
● Act - where you perform actual operation you want to test and
● Assert - when you check results.

12. Sportech project CQRS example