An Introduction to ASP.NET Core MVC

With the release of the new, cross-platform ASP.NET Core, one of the most powerful and established patterns for building web applications is Model-View-Controller (MVC). The MVC pattern helps you build applications that are well-structured, testable, and easier to maintain by separating the application's logic into three interconnected components.

ASP.NET Core MVC is a rich framework for building both web applications and APIs using this pattern.

The Three Components of MVC

1. Model: The Model represents the data and business logic of your application. It's responsible for retrieving and storing data and for implementing the core business rules. The Model is completely independent of the user interface.

2. View: The View is what the user sees. It's responsible for displaying the data from the Model to the user and for sending user actions (like button clicks) to the Controller. In ASP.NET Core, Views are typically written using the Razor syntax, which allows you to embed C# code in your HTML markup.

3. Controller: The Controller is the intermediary between the Model and the View. It handles user input from the View, interacts with the Model to perform actions, and then selects a View to display to the user.

The Request Lifecycle in MVC

Here's how a typical request flows through an ASP.NET Core MVC application:

1. A user makes a request to a URL in their browser.
2. The routing middleware in ASP.NET Core inspects the URL and selects a specific Controller and a specific Action method on that controller to handle the request.
3. The Action method in the Controller interacts with the Model to fetch or update data.
4. The Action method then chooses a View to render and passes the data from the Model to it.
5. The View uses this data to render the final HTML, which is sent back to the user's browser.

A Simple Example

Let's look at the components for a simple page that displays a list of products.

The Model (Product.cs)

This is a simple C# class that represents our data.

public class Product
{
    public int Id { get; set; }
    public string Name { get; set; }
}

The Controller (ProductsController.cs)

This controller has an Index action method that gets a list of products and passes them to a view.

public class ProductsController : Controller
{
    public IActionResult Index()
    {
        // In a real app, you would get this data from a database
        var products = new List<Product>
        {
            new Product { Id = 1, Name = "Laptop" },
            new Product { Id = 2, Name = "Mouse" }
        };

        // Pass the list of products to the view
        return View(products);
    }
}

The View (Views/Products/Index.cshtml)

This Razor view receives the list of products from the controller and renders it as an HTML list.

@model IEnumerable<Product>

<h1>Products</h1>

<ul>
    @foreach (var product in Model)
    {
        <li>@product.Name</li>
    }
</ul>

When a user navigates to /Products/Index, the Index action on the ProductsController is executed, the data is fetched, and the Index.cshtml view is rendered with that data.

Benefits of the MVC Pattern

• Separation of Concerns: By separating the application into three distinct parts, MVC makes the codebase easier to manage and understand. The UI logic is separate from the business logic.
• Testability: Because the Controller is decoupled from the View, it's much easier to write automated unit tests for your application's business logic.
• Parallel Development: Different developers can work on the Model, View, and Controller simultaneously.

Conclusion

The MVC pattern is a powerful and proven way to structure web applications. ASP.NET Core MVC provides a first-class implementation of this pattern, giving you all the tools you need to build scalable, testable, and maintainable web applications on the new, cross-platform .NET Core.