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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.

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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

.Net5 Web API Managing Files Using Azure Blob Storage

In this article, we are going to understand the different file operations like uploading, reading, downloading, and deleting in .Net5 Web API application using Azure Blob Storage. Azure Blob Storage: Azure blob storage is Microsoft cloud storage. Blob storage can store a massive amount of file data as unstructured data. The unstructured data means not belong to any specific type, which means text or binary data. So something like images or pdf or videos to store in the cloud, then the most recommended is to use the blob store. The key component to creating azure blob storage resource: Storage Account:- A Storage account gives a unique namespace in Azure for all the data we will save. Every object that we store in Azure Storage has an address. The address is nothing but the unique name of our Storage Account name. The combination of the account name and the Azure Storage blob endpoint forms the base address for each object in our Storage account. For example, if our Storage Account is n

.Net5 Web API Redis Cache Using StackExchange.Redis.Extensions.AspNetCore Library

In this article, we are going to explore the integration of Redis cache in .Net5 Web API application using the 'StackExchange.Redis.Exntensions' library. Note:- Microsoft has introduced an 'IDistributedCache' interface in dotnet core which supports different cache stores like In-Memory, Redis, NCache, etc. It is simple and easy to work with  'IDistributedCache', for the Redis store with limited features but if we want more features of the Redis store we can choose to use 'StackExchange.Redis.Extensions'.  Click here for Redis Cache Integration Using IDistributedCache Interface . Overview On StackExchange.Redis.Extnesions Library: The 'StackExchange.Redis.Extension' library extended from the main library 'StackExchange.Redis'. Some of the key features of this library like: Default serialization and deserialization. Easy to save and fetch complex objects. Search key. Multiple Database Access Setup Redis Docker Instance: For this sampl

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

Endpoint Routing In Asp.Net Core

How Routing Works In  Core 2.1 And Below Versions?: In Asp.Net Core routing is configured using app.UseRouter() or app.UseMvc() middleware. app.UseMvc(routes => { routes.MapRoute( name: "default", template: "{controller=Home}/{action=Index}/{id?}"); }); Here in Dotnet Core version 2.1 or below versions on the execution of route middleware request will be navigated appropriate controller matched to the route. An operation or functionality which is dependent on route URL or route values and that need to be implemented before the execution of route middleware can be done by accessing the route path from the current request context as below app.Use(async (context, next) => { if(context.Request.Path.Value.IndexOf("oldvehicle") != -1) { context.Response.Redirect("vehicle"); } else { await next(); } }); app.UseMvc(routes => { routes.MapRoute( name: "vehicleRoute", template: "vehicle", defaul

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