CQRS Pattern in C# (Interview Guide)

Most developers answer this question like this:
“CQRS separates read and write.”
That’s correct — but far from enough to impress an interviewer.

What is CQRS?

❌ Bad answer

It separates read and write operations.

✅ Senior answer

CQRS (Command Query Responsibility Segregation) separates read operations (queries) and write operations (commands) into different models.
This allows optimizing each side independently for performance, scalability, and maintainability.

Why use CQRS?

Optimize read and write operations separately
Improve scalability in high-load systems
Clear separation of concerns
Flexible data models for different use cases

Example

// Command
public class CreateOrderCommand {
    public string Product { get; set; }
}

// Query
public class GetOrderQuery {
    public int OrderId { get; set; }
}

When should you use CQRS?

👉 Use CQRS when:

System has complex business logic
Read and write workloads are very different
Need to scale reads and writes independently

⚠️ Avoid CQRS when:

Simple CRUD application
Overengineering is not needed

Common mistakes

❌ Using CQRS everywhere (overengineering)

❌ Not understanding trade-offs (complexity ↑)

❌ Mixing command and query logic again

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