When developers begin exploring scalable architecture patterns in .NET, two concepts often appear side by side: CQRS (Command Query Responsibility Segregation) and MediatR. It’s easy to assume they’re the same — or that one depends on the other. But let’s get this straight:

In this article, we’ll break down what CQRS truly means, how MediatR fits into the picture (if at all), and show real-world examples so you can apply the right concept at the right time.

What is CQRS?

CQRS (Command Query Responsibility Segregation) is a design pattern that separates read and write operations in your system.

In Simple Terms

The idea is to decouple how you handle commands from how you handle queries, potentially allowing different models, teams, or even databases for each.

Example of CQRS (Without MediatR)

  
    // Command
public class CreateOrderCommand
{
    public string ProductId { get; set; }
    public int Quantity { get; set; }
}

// Command Handler
public class OrderCommandHandler
{
    public void Handle(CreateOrderCommand command)
    {
        // Validate and create order
    }
}

// Query
public class GetOrderByIdQuery
{
    public Guid OrderId { get; set; }
}

// Query Handler
public class OrderQueryHandler
{
    public OrderDto Handle(GetOrderByIdQuery query)
    {
        // Fetch and return order from DB
    }
}

Key Points

What is MediatR?

MediatR is a simple .NET library by Jimmy Bogard that helps implement the mediator pattern. It allows sending messages (commands, queries, notifications) without directly referencing the handler.

In Simple Terms

Example of MediatR

  
    // Command
public class CreateOrderCommand : IRequest
{
    public string ProductId { get; set; }
    public int Quantity { get; set; }
}

// Command Handler
public class CreateOrderHandler : IRequestHandler<CreateOrderCommand>
{
    public Task Handle(CreateOrderCommand request, CancellationToken cancellationToken)
    {
        // Handle logic here
        return Task.CompletedTask;
    }
}

// Usage
await _mediator.Send(new CreateOrderCommand { ProductId = "P001", Quantity = 2 });

Why CQRS ≠ MediatR

While MediatR is commonly used in CQRS implementations, especially in .NET apps, it’s not a requirement.

You could

Think of MediatR as a tool in your CQRS toolbox — not the definition of it.

When to Use CQRS Without MediatR

Use CQRS alone when:

Use CQRS with MediatR when:

Summary