Skip to main content

A .Net5 Sample Using CQRS(Command Query Responsibility Segregation) And MediatR Patterns

CQRS stands for Command Query Responsibility Segregation. CQRS guides us to separate our logical implementations into 2 categories like 'Commands', 'Query'. The 'Commands' specifies the operations like creation or updating of data into the data source(database). The 'Query' specifies the operations to fetch the data.

In CQRS models(Request/Response classes) are independent or owned by a single operation, which means model classes can not be shared between the different 'Commands' or different 'Queries' or between a 'Command' and 'Query'.
From the diagram one thing to observe Request/Response model(optional), that's because some times we will use query parameters or return a simple scalar type in those cases we won't create models.

Create .Net5 Web API:

To implement the CQRS pattern let's create a sample .Net5 Web API application.

Configure Entity Framework Core Database Context:

For this demo, I had created a table like 'Products'. So to establish communication between our API project and database, here I will implement Code First Technique with an existing database.

Let's install entity framework core NuGet.
Package Manager Command:
Install-Package Microsoft.EntityFrameworkCore -Version 5.0.4

.Net CLI Command:
dotnet add package Microsoft.EntityFrameworkCore --version 5.0.4
Let's install the SQL server extension library for the entity framework core. 
Package Manager Command:
Install-Package Microsoft.EntityFrameworkCore.SqlServer -Version 5.0.4

.Net CLI Command:
dotnet add package Microsoft.EntityFrameworkCore.SqlServer --version 5.0.4
Let's add the 'Products' table entity. Let's create a folder like 'Data' and inside create a subfolder like 'Entities' and add a file like 'Products.cs'
Data/Entities/Products.cs:
namespace API.CQRS.Sample.Data.Entites
{
    public class Products
    {
        public int ProductId { get; set; }
        public string Name { get; set; }
        public string Manufacturer { get; set; }
        public string Description { get; set; }
        public decimal Price{get;set;}
    }
}
Inside the 'Data' folder create a database context file like 'MyWorldDbContext.cs'
Data/MyWorldDbContext.cs:
public class MyWorldDbContext : DbContext
{
	public MyWorldDbContext(DbContextOptions<MyWorldDbContext> options) : base(options)
	{

	}
	public DbSet<Products> Products { get; set; }
	

	protected override void OnModelCreating(ModelBuilder modelBuilder)
	{
		modelBuilder.Entity<Products>(build => {
			build.HasKey(_ => _.ProductId);
		});
	}
}
In the JSON config file add the connection string
appsettings.Development.json:
"ConnectionStrings":{
"MyWorldDbConnection":"Your_connection_string"
}
Now register database context in the 'Startup.cs' file.
Startup.cs:
services.AddDbContext<MyWorldDbContext>(options =>
{
	options.UseSqlServer(Configuration.GetConnectionString("MyWorldDbConnection"));
});

CQRS Folder Structure:

Let's have a look at the CQRS pattern folder structure.


Create Command Handler To Save A New Product:

So let's begin our sample by creating a command handler to save a new 'Product' into the table. So we have to create a 'RequestModel'(payload class). So in folder hierarchy like 'RequestModels/CommandRequestModels' add a file 'SaveProductRequestModel.cs'.
RequestModels/CommandRequestModels/SaveProductRequestModel.cs:
namespace API.CQRS.Sample.RequestModels.CommandRequestModels
{
    public class SaveProductRequestModel
    {
        public string Name { get; set; }
        public string Manufacturer { get; set; }
        public string Description { get; set; }
        public decimal Price{get;set;}
    }
}
Now let's create an interface with an abstract method to save new products. So folder hierarchy like 'Contracts/CommandHandlers' and add a file like 'ISaveProductCommandHandler.cs'
Contracts/CommandHandler/ISaveProductCommandHandler.cs:
using System.Threading.Tasks;
using API.CQRS.Sample.RequestModels.CommandRequestModels;

namespace API.CQRS.Sample.Contracts.CommandHandlers
{
    public interface ISaveProductCommandHandler
    {
        Task<int> SaveAsync(SaveProductRequestModel requestModel);
    }
}
  • From this method definition, we conclude that this command had only 'RequestModel'(SaveProductRequestMode) but no 'ResponseModel' because its return type is scalar type Integer.
Let's implement the 'SaveAsync' method. In folder hierarchy 'Handlers/CommandHandlers' add a file like 'SaveProductCommandHandler.cs'.
Handlers/CommandHandlers/SaveProductCommandHandler.cs:
using System.Threading.Tasks;
using API.CQRS.Sample.Contracts.CommandHandlers;
using API.CQRS.Sample.Data;
using API.CQRS.Sample.Data.Entites;
using API.CQRS.Sample.RequestModels.CommandRequestModels;

namespace API.CQRS.Sample.Handlers.CommandsHandlers
{
    public class SaveProductCommandHandler: ISaveProductCommandHandler
    {
        public readonly MyWorldDbContext _myWorldDbContext;
        public SaveProductCommandHandler(MyWorldDbContext myWorldDbContext)
        {
            _myWorldDbContext = myWorldDbContext;
        }

        public async Task<int> SaveAsync(SaveProductRequestModel requestModel)
        {
            var newProducts = new Products
            {
                Description = requestModel.Description,
                Manufacturer = requestModel.Manufacturer,
                Name = requestModel.Name,
                Price = requestModel.Price
            };

            _myWorldDbContext.Products.Add(newProducts);
            await _myWorldDbContext.SaveChangesAsync();
            return newProducts.ProductId;
        }
    }
}
Register CommandHandler in 'Startup.cs' file.
Startup.cs:
services.AddScoped<ISaveProductCommandHandler, SaveProductCommandHandler>();
Let's create an endpoint to save our 'Product'. Let's create a new controller like 'ProductController.cs'.
Controller/ProductController.cs:
using System.Threading.Tasks;
using API.CQRS.Sample.Contracts.CommandHandlers;
using API.CQRS.Sample.RequestModels.CommandRequestModels;
using Microsoft.AspNetCore.Mvc;

namespace API.CQRS.Sample.Controllers
{
    [ApiController]
    [Route("[controller]")]
    public class ProductController : ControllerBase
    {
        private readonly ISaveProductCommandHandler _saveProductCommandHandler;
        public ProductController(ISaveProductCommandHandler saveProductCommandHandler)
        {
            _saveProductCommandHandler = saveProductCommandHandler;
        }

        [HttpPost]
        [Route("create")]
        public async Task<IActionResult> SaveProductAsync(SaveProductRequestModel requestModel)
        {
            var result = await _saveProductCommandHandler.SaveAsync(requestModel);
            return Ok(result);
        }
    }
}

Create QueryHandler To Fetch All Products:

Let's begin creating a QueryHandler to fetch all 'Products'. Let's begin by creating a 'ResponseModel'. In the folder hierarchy 'ResponseModels/QueryResponseModels' add a file like 'AllProductsResponseModel'
ResponseModels/QueryResponseModels/AllProductsResponseModel.cs:
namespace API.CQRS.Sample.ResponseModels.QueryResponseModels
{
    public class AllProductsResponseModel
    {
        public int ProductId { get; set; }
        public string Name { get; set; }
        public string Manufacturer { get; set; }
        public string Description { get; set; }
        public decimal Price { get; set; }
    }
}
Now let's declare a abstract method definition in query handler interface to fetch the all 'Products'. In folder hierarchy like 'Contracts/QueryHandlers' add a file 'IAllProductsQueryHandler.cs'.
Contracts/QueryHandlers/IAllProductQueryHandler.cs:
using System.Collections.Generic;
using System.Threading.Tasks;
using API.CQRS.Sample.ResponseModels.QueryResponseModels;

namespace API.CQRS.Sample.Contracts.QueryHandlers
{
    public interface IAllProductsQueryHandler
    {
        Task<List<AllProductsResponseModel>> GetListAsync();
    }
}
  • Here we can observe that our query handler don't have a 'RequestModel', it had 'ResponseModel'(AllProductResponseModel).
Now let's implement logic for abstract method 'GetListAsync'. In folder hierarchy like 'Handlers/QueryHandlers' add a file 'AllProductsQueryHandler.cs'
Handlers/QueryHandlers/AllProductsQueryHandler.cs:
using System.Collections.Generic;
using System.Linq;
using System.Threading.Tasks;
using API.CQRS.Sample.Contracts.QueryHandlers;
using API.CQRS.Sample.Data;
using API.CQRS.Sample.ResponseModels.QueryResponseModels;
using Microsoft.EntityFrameworkCore;

namespace API.CQRS.Sample.Handlers.QueryHandlers
{
    public class AllProductsQueryHandler:IAllProductsQueryHandler
    {
        private readonly MyWorldDbContext _myWorldDbContext;
        public AllProductsQueryHandler(MyWorldDbContext myWorldDbContext)
        {
            _myWorldDbContext = myWorldDbContext;
        }

        public async Task<List<AllProductsResponseModel>> GetListAsync()
        {
            return await _myWorldDbContext.Products
            .Select(_ => new AllProductsResponseModel{
                Description = _.Description,
                ProductId = _.ProductId,
                Manufacturer = _.Manufacturer,
                Name = _.Name,
                Price = _.Price
            }).ToListAsync();
        }
    }
}
Now register our query handler in the 'Startup.cs' file
Startup.cs:
services.AddScoped<IAllProductsQueryHandler,AllProductsQueryHandler>();
Now inject our query handler into the 'ProductController.cs'.
Controllers/ProductController.cs:
private readonly ISaveProductCommandHandler _saveProductCommandHandler;
private readonly IAllProductsQueryHandler _allProductsQueryHandler;
public ProductController(
	ISaveProductCommandHandler saveProductCommandHandler,
	IAllProductsQueryHandler allProductsQueryHandler)
{
	_saveProductCommandHandler = saveProductCommandHandler;
	_allProductsQueryHandler = allProductsQueryHandler;
}
Let's add our new endpoint that fetches all 'Products'.
Controllers/ProductController.cs:
[HttpGet]
[Route("all")]
public async Task<IActionResult> AllProducts()
{
	var result = await _allProductsQueryHandler.GetListAsync();
	return Ok(result);
}

Create Query Handler To Filter Products By Prices:

For better understanding let's create one more query handler that fetches the 'Products' by price range. Let's create 'ResponseModel' in the folder hierarchy like 'ResponeModels/QueryResponeModels' add a file like 'PriceRangeProductsResponseModel.cs'.
ResponseModels/QueryResponseModels/PriceRangeProductsResponseModel.cs:
namespace API.CQRS.Sample.ResponseModels.QueryResponseModels
{
    public class PriceRangeProductsResponseModel
    {
        public int ProductId { get; set; }
        public string Name { get; set; }
        public decimal Price { get; set; }
    }
}
Now let's define abstract method in our query handler interface. In the folder hierarchy like 'Contracts/QueryHandlers' add a file like 'IPriceRangeProductsQueryHandler.cs'
Contracts/QueryHandlers/IPriceRangeProductsQueryHandler.cs:
using System.Collections.Generic;
using System.Threading.Tasks;
using API.CQRS.Sample.ResponseModels.QueryResponseModels;

namespace API.CQRS.Sample.Contracts.QueryHandlers
{
    public interface IPriceRangeProductsQueryHandler
    {
        Task<List<PriceRangeProductsResponseModel>> PriceRangeProductsAsync(int minPrice, int maxPrice);
    }
}
Now let's implement the 'PriceRangeProductsAsync' method. In the folder hierarchy like 'Handlers/QueryHandlers' add a file like 'PriceRangeProductsQueryHandler.cs'.
Handlers/QueryHandlers/PriceRangeProductsQueryHandler.cs:
using System.Collections.Generic;
using System.Linq;
using System.Threading.Tasks;
using API.CQRS.Sample.Contracts.QueryHandlers;
using API.CQRS.Sample.Data;
using API.CQRS.Sample.ResponseModels.QueryResponseModels;
using Microsoft.EntityFrameworkCore;

namespace API.CQRS.Sample.Handlers.QueryHandlers
{
    public class PriceRangeProductsQueryHandler : IPriceRangeProductsQueryHandler
    {
        private readonly MyWorldDbContext _myWorldDbContext;
        public PriceRangeProductsQueryHandler(MyWorldDbContext myWorldDbContext)
        {
            _myWorldDbContext = myWorldDbContext;
        }
        public async Task<List<PriceRangeProductsResponseModel>> PriceRangeProductsAsync(int minPrice, int maxPrice)
        {
            return await _myWorldDbContext.Products
            .Where(_ => _.Price >= minPrice && _.Price <= maxPrice)
            .Select(_ => new PriceRangeProductsResponseModel
            {
                Name = _.Name,
                ProductId = _.ProductId,
                Price = _.Price
            }).ToListAsync();
        }
    }
}
Register the query handlers in the 'Startup.cs'.
Startup.cs:
services.AddScoped<IPriceRangeProductsQueryHandler, PriceRangeProductsQueryHandler>();
Now inject the query handler into the 'ProductController.cs'
Controllers/ProductController.cs:
[HttpGet]
[Route("price-range")]
public async Task<IActionResult> PriceRangeProducts(int minPrice, int maxPrice)
{
	var result = await _priceRangeProductsQueryHandler.PriceRangeProductsAsync(minPrice, maxPrice);
	return Ok(result);
}
Finally we have completed our sample by implementing few Query/Command handlers. So our project folder structure will looks like:


MediatR:

MediatR is another design pattern. MediatR builds with handlers that have the capability to work on Commands and Queries.

MediatR reduces a lot of boilerplate code like injecting multiple services into the controller. MediatR provides a single entry point that expects a RequestModel, so based on the RequestModel corresponding Handler gets invoked. It works as a centralized communication hub because from the controller any handler gets invoked only through it. So it's the most common recommendation to use MediatR with CQRS.
From the diagram, we have to understand MediatR should have both RequestModel and ResponseMode. In MediatR 'RequestModel' always be a user-defined class whereas 'ResponseModel' either a user-defined class or scalar type.

Install MediatR NuGet:

Let's install the MediatR package for dotnet.
Package Manager Command:
Install-Package MediatR -Version 9.0.0

.Net CLI Command:
dotnet add package MediatR --version 9.0.0
Let's install the Dependency Injection extension library for MediatR. 
Package Manager Command:
Install-Package MediatR.Extensions.Microsoft.DependencyInjection -Version 9.0.0

.Net CLI Command:
dotnet add package MediatR.Extensions.Microsoft.DependencyInjection --version 9.0.0

Register And Inject MediatR:

Let's register MediatR service in 'Startup.cs'
Startup.cs:
services.AddMediatR(Assembly.GetExecutingAssembly());
Now inject the 'IMediator' into the 'ProductController' constructor.
Controllers/ProductController.cs:
private readonly ISaveProductCommandHandler _saveProductCommandHandler;
private readonly IAllProductsQueryHandler _allProductsQueryHandler;
private readonly IPriceRangeProductsQueryHandler _priceRangeProductsQueryHandler;
private readonly IMediator _mediator;
public ProductController(
	ISaveProductCommandHandler saveProductCommandHandler,
	IAllProductsQueryHandler allProductsQueryHandler,
	IPriceRangeProductsQueryHandler priceRangeProductsQueryHandler,
	IMediator mediator)
{
	_saveProductCommandHandler = saveProductCommandHandler;
	_allProductsQueryHandler = allProductsQueryHandler;
	_priceRangeProductsQueryHandler = priceRangeProductsQueryHandler;
	_mediator = mediator;
}

Update Logic In Command Handler To Save A New Product Using MediatR:

In MediatR pattern 'RequestModel' required, based on the 'RequestModel' corresponding handler will be automatically invoked by the MedaitR. The 'RequesModel' should always be a user-define class. In folder hierarchy 'RequestModels/CommandRequestModels' update the 'SaveProductRequestModel.cs' like below:
RequestModels/CommandRequestModels/SaveProductRequestModel.cs:
using MediatR;

namespace API.CQRS.Sample.RequestModels.CommandRequestModels
{
    public class SaveProductRequestModel:IRequest<int>
    {
        public string Name { get; set; }
        public string Manufacturer { get; set; }
        public string Description { get; set; }
        public decimal Price{get;set;}
    }
}
  • In mediatr pattern our RequestModels(eg: SaveProductRequestModel) should inherit 'IRequest<out ResponseModel>'. The 'IRequest<out T>' 'T' model should be the 'ResponseModel' our handler.
 Now we have to update the logic of our command handler 'SaveProductCommandHandler.cs'.
 Handlers/CommandHandlers/SaveProductCommandHandler.cs:
using System.Threading;
using System.Threading.Tasks;
using API.CQRS.Sample.Contracts.CommandHandlers;
using API.CQRS.Sample.Data;
using API.CQRS.Sample.Data.Entites;
using API.CQRS.Sample.RequestModels.CommandRequestModels;
using MediatR;

namespace API.CQRS.Sample.Handlers.CommandsHandlers
{
    public class SaveProductCommandHandler : IRequestHandler<SaveProductRequestModel, int>
    {
        public readonly MyWorldDbContext _myWorldDbContext;
        public SaveProductCommandHandler(MyWorldDbContext myWorldDbContext)
        {
            _myWorldDbContext = myWorldDbContext;
        }

        public async Task<int> Handle(SaveProductRequestModel request, CancellationToken cancellationToken)
        {
            var newProducts = new Products
            {
                Description = request.Description,
                Manufacturer = request.Manufacturer,
                Name = request.Name,
                Price = request.Price
            };

            _myWorldDbContext.Products.Add(newProducts);
            await _myWorldDbContext.SaveChangesAsync();
            return newProducts.ProductId;
        }
    }
}
  • By using MediatR, we no need to create interfaces to our Command/Query handlers. So we can delete all our interface classes inside of the 'Contracts' folder in our project.
  • Our Command Handler inherits 'MediatR.IRequestHandler<in TRequest, TResponse>'. The 'TRequest' means our 'RequestModel'(only user defined class), 'TResponse' means our 'ResponseModel'(either user defined class or scalar type).
  • Our Command Handler should implement 'Handle' as a public method. So first input parameter of the 'Handle' is 'RequestModel'. The 'Handle' method return type is our 'ResponseModel'.
Now we need to comment out our 'ISaveProductCommandHandler' references in 'Startup.cs' and then in 'ProductControll.cs' as well.

Let's update our endpoint to use MediatR to trigger our Command Handler.
Controllers/ProductController.cs:
[HttpPost]
[Route("create")]
public async Task<IActionResult> SaveProductAsync(SaveProductRequestModel requestModel)
{
	//var result = await _saveProductCommandHandler.SaveAsync(requestModel);
	var result = await _mediator.Send(requestModel);
	return Ok(result);
}
  • So here 'Send' method of 'IMediator' that takes our RequestModel(eg: SaveProductRequestModel) as input value. So 'Send' method will invoke the appropriate Command Handler(eg: SaveProductCommandHandler) with the help of 'RequestModel'(eg: SaveProductRequestModel).

Update Logic In QueryHandler To Fetch All Products Using MediatR:

Currently 'AllProductsQueryHandler' class has method 'GetListAsync' that don't have 'RequestModel'. But we know MediatR fully depends on the 'RequestModel'. So we have to create an empty 'RequestModel' to make it work with 'MediatR'. In folder hierarchy like 'RequestModel/QueryRequestModels' add a new file like 'AllProductsRequestModel.cs'
RequestModel/QueryRequestModels/AllProductsRequestModel.cs:
using System.Collections.Generic;
using API.CQRS.Sample.ResponseModels.QueryResponseModels;
using MediatR;

namespace API.CQRS.Sample.RequestModels.QueryRequestModels
{
    public class AllProductsRequestModel:IRequest<List<AllProductsResponseModel>>
    {

    }
}
  • In mediatr pattern our RequestModels(eg: AllProductsRequestModel) should inherit 'IRequest<out ResponseModel>'. The 'IRequest<out T>' 'T' model should be the 'ResponseModel'(eg: List<AllProductsResponseModel>) of our handler.
Update the logic of our query handler 'AllProductsQueryHandler'.
Handlers/QueryHandlers/AllProductsQueryHandler.cs:
using System.Collections.Generic;
using System.Linq;
using System.Threading;
using System.Threading.Tasks;
using API.CQRS.Sample.Contracts.QueryHandlers;
using API.CQRS.Sample.Data;
using API.CQRS.Sample.RequestModels.QueryRequestModels;
using API.CQRS.Sample.ResponseModels.QueryResponseModels;
using MediatR;
using Microsoft.EntityFrameworkCore;

namespace API.CQRS.Sample.Handlers.QueryHandlers
{
    public class AllProductsQueryHandler : IRequestHandler<AllProductsRequestModel, List<AllProductsResponseModel>>
    {
        private readonly MyWorldDbContext _myWorldDbContext;
        public AllProductsQueryHandler(MyWorldDbContext myWorldDbContext)
        {
            _myWorldDbContext = myWorldDbContext;
        }
        public async Task<List<AllProductsResponseModel>> Handle(AllProductsRequestModel request, CancellationToken cancellationToken)
        {
            return await _myWorldDbContext.Products
            .Select(_ => new AllProductsResponseModel
            {
                Description = _.Description,
                ProductId = _.ProductId,
                Manufacturer = _.Manufacturer,
                Name = _.Name,
                Price = _.Price
            }).ToListAsync();
        }
    }
}
  • Our Query Handler inherits 'MediatR.IRequestHandler<in TRequest, TResponse>'. The 'TRequest' means our 'RequestModel'(only user defined class), 'TResponse' means our 'ResponseModel'(either user defined class or scalar type).
  • Our Query Handler should implement 'Handle' as a public method. So first input parameter of the 'Handle' is 'RequestModel'(eg: AllProductsRequestModel). The 'Handle' method return type is our 'ResponseModel'(eg: List<AllProductsResponseModel>).
Now we can remove the reference of our interface 'IAllProductsQueryHandler', in 'Startup.cs' and in the constructor of the 'ProductController' as well.

Update the endpoint logic to use Mediator to invoke the query handler.
Controllers/ProductController.cs:
[HttpGet]
[Route("all")]
public async Task<IActionResult> AllProducts()
{
	//var result = await _allProductsQueryHandler.GetListAsync();
	var result = await _mediator.Send(new AllProductsRequestModel());
	return Ok(result);
}
  • So here 'Send' method of 'IMediator' that takes our RequestModel(eg: AllProductsRequestModel) as input value. So 'Send' method will invoke the appropriate Query Handler(eg: AllProductsQueryHandler) with the help of 'RequestModel'(eg: AllProductsRequestModel).

Update Logic In Query Handler To Filter Products By Prices Using MediatR:

Currently 'PriceRangeProductsQueryHandler' has method 'PriceRangeProductsAsync' that contains 2 input parameters like 'minPrice' and 'maxPrice'. Now we have to create 'RequestModel' with those input properties to support MediatR. In the folder hierarchy like 'RequestModel/QueryRequestModels' add a new file like 'PriceRangeProductsRequestModel.cs'
RequestModel/QueryRequestModels/PriceRangeProductsRequestModel.cs:
using System.Collections.Generic;
using API.CQRS.Sample.ResponseModels.QueryResponseModels;
using MediatR;

namespace API.CQRS.Sample.RequestModels.QueryRequestModels
{
    public class PriceRangeProductsRequestModel:IRequest<List<PriceRangeProductsResponseModel>>
    {
        public int MinPrice { get; set; }
        public int MaxPrice { get; set; }
    }
}
  • In mediatr pattern our RequestModels(eg: PriceRangeProductsRequestModel) should inherit 'IRequest<out ResponseModel>'. The 'IRequest<out T>' 'T' model should be the 'ResponseModel'(eg: List<PriceRangeProductsResponseModel>) of our handler.
Let's update the logic of the query handler 'PriceRangeProductsQueryHandler'.
Handlers/QueryHandlers/PriceRangeProductsQueryHandler.cs:
using System.Collections.Generic;
using System.Linq;
using System.Threading;
using System.Threading.Tasks;
using API.CQRS.Sample.Contracts.QueryHandlers;
using API.CQRS.Sample.Data;
using API.CQRS.Sample.RequestModels.QueryRequestModels;
using API.CQRS.Sample.ResponseModels.QueryResponseModels;
using MediatR;
using Microsoft.EntityFrameworkCore;

namespace API.CQRS.Sample.Handlers.QueryHandlers
{

    public class PriceRangeProductsQueryHandler : IRequestHandler<PriceRangeProductsRequestModel, List<PriceRangeProductsResponseModel>>
    {
        private readonly MyWorldDbContext _myWorldDbContext;
        public PriceRangeProductsQueryHandler(MyWorldDbContext myWorldDbContext)
        {
            _myWorldDbContext = myWorldDbContext;
        }
        public async Task<List<PriceRangeProductsResponseModel>> Handle(PriceRangeProductsRequestModel request, CancellationToken cancellationToken)
        {
            
            return await _myWorldDbContext.Products
            .Where(_ => _.Price >= request.MinPrice && _.Price <= request.MaxPrice)
            .Select(_ => new PriceRangeProductsResponseModel
            {
                Name = _.Name,
                ProductId = _.ProductId,
                Price = _.Price
            }).ToListAsync();
        }
    }
}
  • Our Query Handler inherits 'MediatR.IRequestHandler<in TRequest, TResponse>'. The 'TRequest' means our 'RequestModel'(only user defined class), 'TResponse' means our 'ResponseModel'(either user defined class or scalar type).
  • Our Query Handler should implement 'Handle' as a public method. So first input parameter of the 'Handle' is 'RequestModel'(eg: PriceRangeProductsRequestModel). The 'Handle' method return type is our 'ResponseModel'(eg: List<PriceRangeProductsResponseModel>).
Now we remove references of our interface 'IPriceRangeProductsQueryHandler' in 'Startup.cs' and in 'ProductController' as well.

Now update the endpoint logic to use the MediatR.
Controllers/ProductController.cs:
[HttpGet]
[Route("price-range")]
public async Task<IActionResult> PriceRangeProducts([FromQuery]PriceRangeProductsRequestModel requestModel)
{
	//var result = await _priceRangeProductsQueryHandler.PriceRangeProductsAsync(minPrice, maxPrice);
	var result = await _mediator.Send(requestModel);
	return Ok(result);
}
  • So here 'Send' method of 'IMediator' that takes our RequestModel(eg: PriceRangeProductsRequestModel) as input value. So 'Send' method will invoke the appropriate Query Handler(eg: PriceRangeProductsQueryHandler) with the help of 'RequestModel'(eg: PriceRangeProductsRequestModel).
That's all we have implemented .Net5 Web API sample using CQRS And MediatR Patterns.

Video Session:

 

Support Me!
Buy Me A Coffee PayPal Me

Wrapping Up:

Hopefully, I think this article delivered some useful information on CQRS and MediatR patterns. I love to have your feedback, suggestions, and better techniques in the comment section below.

Refer:

Follow Me:

Labels:

Comments

Post a Comment

Popular posts from this blog

.NET6 Web API CRUD Operation With Entity Framework Core

In this article, we are going to do a small demo on AspNetCore 6 Web API CRUD operations. What Is Web API: Web API is a framework for building HTTP services that can be accessed from any client like browser, mobile devices, desktop apps. In simple terminology API(Application Programming Interface) means an interface module that contains a programming function that can be requested via HTTP calls to save or fetch the data for their respective clients. Some of the key characteristics of API: Supports HTTP verbs like 'GET', 'POST', 'PUT', 'DELETE', etc. Supports default responses like 'XML' and 'JSON'. Also can define custom responses. Supports self-hosting or individual hosting, so that all different kinds of apps can consume it. Authentication and Authorization are easy to implement. The ideal platform to build REST full services. Create A .NET6 Web API Application: Let's create a .Net6 Web API sample application to accomplish our
6 comments
Read more

Angular 14 Reactive Forms Example

In this article, we will explore the Angular(14) reactive forms with an example. Reactive Forms: Angular reactive forms support model-driven techniques to handle the form's input values. The reactive forms state is immutable, any form filed change creates a new state for the form. Reactive forms are built around observable streams, where form inputs and values are provided as streams of input values, which can be accessed synchronously. Some key notations that involve in reactive forms are like: FormControl - each input element in the form is 'FormControl'. The 'FormControl' tracks the value and validation status of form fields. FormGroup - Track the value and validate the state of the group of 'FormControl'. FormBuilder - Angular service which can be used to create the 'FormGroup' or FormControl instance quickly. Form Array - That can hold infinite form control, this helps to create dynamic forms. Create An Angular(14) Application: Let'
3 comments
Read more

Part-1 Angular JWT Authentication Using HTTP Only Cookie[Angular V13]

In this article, we are going to implement a sample angular application authentication using HTTP only cookie that contains a JWT token. HTTP Only JWT Cookie: In a SPA(Single Page Application) Authentication JWT token either can be stored in browser 'LocalStorage' or in 'Cookie'. Storing JWT token inside of the cookie then the cookie should be HTTP Only. The HTTP-Only cookie nature is that it will be only accessible by the server application. Client apps like javascript-based apps can't access the HTTP-Only cookie. So if we use authentication with HTTP only JWT cookie then we no need to implement custom logic like adding authorization header or storing token data, etc at our client application. Because once the user authenticated cookie will be automatically sent to the server by the browser on every API call. Authentication API: To implement JWT cookie authentication we need to set up an API. For that, I had created a mock authentication API(Using the NestJS Se
Post a Comment
Read more

Unit Testing Asp.NetCore Web API Using xUnit[.NET6]

In this article, we are going to write test cases to an Asp.NetCore Web API(.NET6) application using the xUnit. xUnit For .NET: The xUnit for .Net is a free, open-source, community-focused unit testing tool for .NET applications. By default .Net also provides a xUnit project template to implement test cases. Unit test cases build upon the 'AAA' formula that means 'Arrange', 'Act' and 'Assert' Arrange - Declaring variables, objects, instantiating mocks, etc. Act - Calling or invoking the method that needs to be tested. Assert - The assert ensures that code behaves as expected means yielding expected output. Create An API And Unit Test Projects: Let's create a .Net6 Web API and xUnit sample applications to accomplish our demo. We can use either Visual Studio 2022 or Visual Studio Code(using .NET CLI commands) to create any.Net6 application. For this demo, I'm using the 'Visual Studio Code'(using the .NET CLI command) editor. Create a fo
6 comments
Read more

A Small Guide On NestJS Queues

NestJS Application Queues helps to deal with application scaling and performance challenges. When To Use Queues?: API request that mostly involves in time taking operations like CPU bound operation, doing them synchronously which will result in thread blocking. So to avoid these issues, it is an appropriate way to make the CPU-bound operation separate background job.  In nestjs one of the best solutions for these kinds of tasks is to implement the Queues. For queueing mechanism in the nestjs application most recommended library is '@nestjs/bull'(Bull is nodejs queue library). The 'Bull' depends on Redis cache for data storage like a job. So in this queueing technique, we will create services like 'Producer' and 'Consumer'. The 'Producer' is used to push our jobs into the Redis stores. The consumer will read those jobs(eg: CPU Bound Operations) and process them. So by using this queues technique user requests processed very fastly because actually
7 comments
Read more

Angular 14 State Management CRUD Example With NgRx(14)

In this article, we are going to implement the Angular(14) state management CRUD example with NgRx(14) NgRx Store For State Management: In an angular application to share consistent data between multiple components, we use NgRx state management. Using NgRx state helps to avoid unwanted API calls, easy to maintain consistent data, etc. The main building blocks for the NgRx store are: Actions - NgRx actions represents event to trigger the reducers to save the data into the stores. Reducer - Reducer's pure function, which is used to create a new state on data change. Store - The store is the model or entity that holds the data. Selector - Selector to fetch the slices of data from the store to angular components. Effects - Effects deals with external network calls like API. The effect gets executed based the action performed Ngrx State Management flow: The angular component needs data for binding.  So angular component calls an action that is responsible for invoking the API call.  Aft
7 comments
Read more

Usage Of CancellationToken In Asp.Net Core Applications

When To Use CancellationToken?: In a web application request abortion or orphan, requests are quite common. On users disconnected by network interruption or navigating between multiple pages before proper response or closing of the browser, tabs make the request aborted or orphan. An orphan request can't deliver a response to the client, but it will execute all steps(like database calls, HTTP calls, etc) at the server. Complete execution of an orphan request at the server might not be a problem generally if at all requests need to work on time taking a job at the server in those cases might be nice to terminate the execution immediately. So CancellationToken can be used to terminate a request execution at the server immediately once the request is aborted or orphan. Here we are going to see some sample code snippets about implementing a CancellationToken for Entity FrameworkCore, Dapper ORM, and HttpClient calls in Asp.NetCore MVC application. Note: The sample codes I will show in
2 comments
Read more

Blazor WebAssembly Custom Authentication From Scratch

In this article, we are going to explore and implement custom authentication from the scratch. In this sample, we will use JWT authentication for user authentication. Main Building Blocks Of Blazor WebAssembly Authentication: The core concepts of blazor webassembly authentication are: AuthenticationStateProvider Service AuthorizeView Component Task<AuthenticationState> Cascading Property CascadingAuthenticationState Component AuthorizeRouteView Component AuthenticationStateProvider Service - this provider holds the authentication information about the login user. The 'GetAuthenticationStateAsync()' method in the Authentication state provider returns user AuthenticationState. The 'NotifyAuthenticationStateChaged()' to notify the latest user information within the components which using this AuthenticationStateProvider. AuthorizeView Component - displays different content depending on the user authorization state. This component uses the AuthenticationStateProvider
6 comments
Read more

How Response Caching Works In Asp.Net Core

What Is Response Caching?: Response Caching means storing of response output and using stored response until it's under it's the expiration time. Response Caching approach cuts down some requests to the server and also reduces some workload on the server. Response Caching Headers: Response Caching carried out by the few Http based headers information between client and server. Main Response Caching Headers are like below Cache-Control Pragma Vary Cache-Control Header: Cache-Control header is the main header type for the response caching. Cache-Control will be decorated with the following directives. public - this directive indicates any cache may store the response. private - this directive allows to store response with respect to a single user and can't be stored with shared cache stores. max-age - this directive represents a time to hold a response in the cache. no-cache - this directive represents no storing of response and always fetch the fr
Post a Comment
Read more

Angular 14 Crud Example

In this article, we will implement CRUD operation in the Angular 14 application. Angular: Angular is a framework that can be used to build a single-page application. Angular applications are built with components that make our code simple and clean. Angular components compose of 3 files like TypeScript File(*.ts), Html File(*.html), CSS File(*.cs) Components typescript file and HTML file support 2-way binding which means data flow is bi-directional Component typescript file listens for all HTML events from the HTML file. Create Angular(14) Application: Let's create an Angular(14) application to begin our sample. Make sure to install the Angular CLI tool into our local machine because it provides easy CLI commands to play with the angular application. Command To Install Angular CLI npm install -g @angular/cli Run the below command to create the angular application. Command To Create Angular Application ng new name_of_your_app Note: While creating the app, you will see a noti
4 comments
Read more