Using the Command Query Responsibility Segregation (CQRS) Pattern in .NET

Introduction

The Command Query Responsibility Segregation (CQRS) pattern separates the read and write operations for data. In this tutorial, we will explore how to implement CQRS in .NET applications to achieve scalability and separation of concerns.

Prerequisites

Before we begin, make sure you have the following:

• .NET SDK installed
• Visual Studio or Visual Studio Code (optional)
• Basic understanding of ASP.NET Core

Setting Up the Project

Create a new ASP.NET Core project to implement the CQRS pattern.

dotnet new webapi -n MyCqrsApp
cd MyCqrsApp

Implementing Commands and Queries

Define commands for write operations and queries for read operations. Commands will modify the application state, while queries will fetch data.

Example Command

// Commands/CreateProductCommand.cs
public class CreateProductCommand
{
    public string Name { get; set; }
    public decimal Price { get; set; }
}

Example Query

// Queries/GetAllProductsQuery.cs
public class GetAllProductsQuery
{
}

Implementing Command Handlers

Create command handlers to handle and process commands.

Example Command Handler

// Commands/CreateProductCommandHandler.cs
public class CreateProductCommandHandler
{
    public async Task<bool> Handle(CreateProductCommand command)
    {
        // Logic to create a new product
        return true;
    }
}

Implementing Query Handlers

Create query handlers to handle and process queries.

Example Query Handler

// Queries/GetAllProductsQueryHandler.cs
public class GetAllProductsQueryHandler
{
    public async Task<IEnumerable<Product>> Handle(GetAllProductsQuery query)
    {
        // Logic to fetch all products
        return await _productRepository.GetAllAsync();
    }
}

Configuring Dependency Injection

Register command and query handlers in the dependency injection container.

Example Dependency Injection Configuration

// Startup.cs
public void ConfigureServices(IServiceCollection services)
{
    services.AddTransient<CreateProductCommandHandler>();
    services.AddTransient<GetAllProductsQueryHandler>();
}

Using MediatR for CQRS Implementation

Use MediatR library to mediate between commands and handlers, and queries and handlers.

Example MediatR Configuration

// Startup.cs
public void ConfigureServices(IServiceCollection services)
{
    services.AddMediatR(typeof(Startup).Assembly);
}

Testing CQRS Operations

Test command and query handlers to ensure they perform as expected.

Conclusion

In this tutorial, we explored how to implement the Command Query Responsibility Segregation (CQRS) pattern in .NET applications. We defined commands and queries, implemented command and query handlers, configured dependency injection, and used MediatR to mediate between commands/queries and handlers. By adopting CQRS, you can achieve better scalability and separation of concerns in your .NET applications.