The goal of this blog post is simple..
First, we talk about CQRS software pattern and its use cases… why it is so damn important to have a decoupled application achieved by the CQRS Pattern
CQRS Pattern
This image below explains about two models within the Application layer, which is the Query and Command model.

The Front-End UI communicates with these models to create, update, safe and
Why CQRS?
Single Responsibility
Single Responsibility is a computer programming principle. It states that every module or class should have responsibility for a single part of the functionality provided by the software. Therefore, all entities are each a Single Responsibility.
Benefits of Single Responsibility:
- It makes it easier to edit and add functionality to a class/model that has a single responsibility
- Will achieve loosely coupled application
- Independent of framework
Code is more readable and understandable
This is how I segregate the
Command and Query Responsibility Segregation pattern
[ApplicationName].Core.Application


As you can see above, I have a Customers folder and inside that folder contains the commands, models, queries
, and validators.
For example in my case, I have a “CreateCustomerCommand.cs'” and “CreateCustomerCommandHandler” in the Commands folder. I also have “get” classes which are structured similarly in naming convention; “GetAllCustomersQuery.cs” and “GetAllCustomersQueryHandler.cs“.
The Commands are for Creating, Updating and Deleting objects/entities. The queries are for searching and getting data back out from the database.
An
Entity definition for the haters

MediatR – Jimmy Bogard
So this guy Jimmy did a great job on implementing a library for the function of CQRS pattern. Benefits include:
- Simple mediator implementation in .NET
- In-process messaging with no dependencies.
- Supports request/response, commands, queries, notifications and events, synchronous and async with intelligent dispatching via C# generic variance.
- Any block can opt into these alignments. The embed block has them also, and is responsive out of the box:
Using MediatR in ASP.Net Core was slightly tricky, not many out there with the correct implementation. It actually is very simple, but it took me some time to figure it all out. (I’m not a newbie in the .NET Framework)
Here is some code for in the StartUp.cs class you can use to register the MediatR service:
// ADD MediatR |
services.AddMediatR(); |
services.AddMediatR(typeof(CreateCustomerCommand).Assembly, typeof(CreateCustomerCommandHandler).Assembly); |
See what I did there uptop, I registered the Command and the Command Handler
Don’t forget to do this!
The controllers in the MVC model will reference these commands, queries.
The beauty is that MediatR handles the requests in the pipeline.
A “CreateCustomerCommand.cs” implementation:
namespace QAEngine.Application.Customers.Command
{
public class CreateCustomerCommand : IRequest
{
public string Id { get; set; }
public string Title { get; set; }
public string FirstName { get; set; }
public string LastName { get; set; }
public string Address { get; set; }
public string City { get; set; }
public string Region { get; set; }
public string PostalCode { get; set; }
public string Country { get; set; }
public string Phone { get; set; }
public DateTime AccountCreated { get; set; }
public DateTime DateOfBirth { get; set; }
}
}
A “CreateCustomerCommandHandler.cs” implementation:
namespace QAEngine.Application.Customers.Command
{
public class CreateCustomerCommandHandler : IRequestHandler
{
private readonly QAEngineDbContext _context;
public CreateCustomerCommandHandler(QAEngineDbContext context)
{
_context = context;
}
public async Task<CustomerModel> Handle(CreateCustomerCommand
request, CancellationToken cancellationToken)
{
var entity = new Customer
{
CustomerId = request.Id,
Title = request.Title,
FirstName = request.FirstName,
LastName = request.LastName,
Address = request.Address,
City = request.City,
Region = request.Region,
PostalCode = request.PostalCode,
Country = request.Country,
Phone = request.Phone,
AccountCreated = request.AccountCreated,
DateOfBirth = request.DateOfBirth.Date
};
_context.Customers.Add(entity);
await _context.SaveChangesAsync(cancellationToken);
return CustomerModel.Create(entity);
}
}
}
Finally, Here is my Customer controller, where I utilise these beautiful implementations <3
[HttpGet()]
public Task<List<CustomerListModel>> ViewCustomers()
{
return Mediator.Send(new GetCustomerListQuery());
}
[HttpGet("{id}")]
public async Task<IActionResult> FindACustomer(string id)
{
return Ok(await Mediator.Send(new GetCustomerModelQuery { Id = id }));
}
[Authorize]
public IActionResult NewCustomer()
{
return View();
}
[Authorize]
[HttpPost]
//noteToSelf = FromForm means from the bloody form not [FromBody]
public async Task<IActionResult> NewCustomer([FromForm]CreateCustomerCommand command)
{
return Ok(await Mediator.Send(command));
}
[HttpPut("{id}")]
public async Task<IActionResult> UpdateCustomerDetails(string id, [FromBody]UpdateCustomerCommand command)
{
if (command == null || command.Id != id)
{
return BadRequest();
}
return Ok(await Mediator.Send(command));
}
[HttpDelete("{id}")]
public async Task<IActionResult> DeleteCustomer(string id)
{
await Mediator.Send(new DeleteCustomerCommand { Id = id });
return NoContent();
}
Code is Poetry
G
Read my journey: https://www.bilaalsblog.com/pilot-a-software-developers-journey-and-the-amount-of-coffees-consumed/

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Kudos!
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Hello there,
Yes blogs do use WYSIWYG editors.. WordPress is a great platform! and it always has been!
What are you going to blog about?
Hello,
Very nice blog. I am trying to explore CQRS/MediatR approach for some time now.
I always lack examples of some more complex scenario with CQRS/MediatR. I work on a relatively big enterprise project in healthcare that is ready for change. Do you maybe have experience with applications implemented in this pattern that have high and heavy traffic ? I am interested in cons of using in-process messages. Also healthcare data is very interconnected and sometimes I am not sure about separation.
Thanks! Cheers!
Hi Tarik
Separation is always best. When you mention healthcare i think of micro services. These are services which are totally loosely coupled to one another. All micro-services contain their own endpoint in the API design as well as a direct route to the database. A micro-services architecture would be best suited for you since this architecture will provide both speed and reliability. Deploying micro-services to the cloud will further enhance the design and architecture.
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