CQRS in .NET

🚀 CQRS in .NET — What It Is, When to Use It, and When to Avoid It

CQRS (Command Query Responsibility Segregation) is one of the most misunderstood patterns in .NET.

It’s often:

• Over-engineered
• Confused with Event Sourcing
• Applied where CRUD is perfectly fine

Let’s demystify it.

🧠 What CQRS Actually Means

CQRS says one simple thing:

Commands change state. Queries read state. They are different concerns.

That’s it.

No messaging. No events. No microservices required.

✍️ Basic Example

Command (write)

public record CreateOrderCommand(Guid CustomerId);

Command handler

public class CreateOrderHandler
{
    public Task Handle(CreateOrderCommand command)
    {
        // validate
        // modify state
        // persist
    }
}

Query (read)

public record GetOrderByIdQuery(Guid OrderId);

Query handler

public class GetOrderByIdHandler
{
    public Task<OrderDto?> Handle(GetOrderByIdQuery query)
    {
        // read only
        // no side effects
    }
}

Reads and writes are explicitly separated.

🎯 Why CQRS Can Be Powerful

1️⃣ Different Models for Reads and Writes

Writes:

• Enforce invariants
• Use rich domain models

Reads:

• Optimized DTOs
• Joins, projections, denormalization

No more “one model to rule them all”.

2️⃣ Clear Intent

CreateOrderCommand
GetOrdersForCustomerQuery

The name tells you:

• What happens
• Whether state changes

This improves maintainability and onboarding.

3️⃣ Natural Fit for Validation & Security

Commands:

• Validate business rules
• Enforce authorization

Queries:

• Read-only
• Often simpler and faster

⚠️ When CQRS Is Overkill

CQRS is not free.

Avoid it when:

• ❌ Your app is simple CRUD
• ❌ You have a small codebase
• ❌ Team is unfamiliar with the pattern
• ❌ You don’t have real complexity

CQRS adds more files, more concepts, more indirection.

🧠 CQRS ≠ Event Sourcing

Very important distinction:

• CQRS → separates reads and writes
• Event Sourcing → stores events as source of truth

You can use CQRS without events. You can use events without CQRS.

They are independent patterns.

🏗️ CQRS in Modern .NET

Most teams use Lightweight CQRS:

• Same database
• Same transaction
• Same deployment
• Different code paths

Often implemented with:

• MediatR (or similar)
• Explicit command/query handlers
• DTOs for queries

⚖️ CRUD vs CQRS — Quick Comparison

🎯 Final Takeaway

CQRS is not about scale. It’s about clarity.

If your domain has:

• Complex business rules
• Different read/write needs
• Growing maintenance cost

CQRS can bring order.

If not — don’t force it.

Patterns should reduce complexity, not create it.

#dotnet #csharp #cqrs #softwarearchitecture #cleancode #backend