Explain in Details: ASP.NET MVC Asynchronous Programming with async and await

Introduction to Asynchronous Programming

In the world of web development, particularly in ASP.NET MVC, handling high traffic efficiently and providing a responsive user experience are critical. One powerful tool to achieve this is asynchronous programming. ASP.NET MVC supports asynchronous programming through the use of async and await keywords, which help in improving the scalability and performance of web applications.

Understanding Asynchronous Programming

Asynchronous programming allows a program to perform multiple operations concurrently, thus freeing up resources and improving the responsiveness of the application. In a synchronous model, if a function waits for a task to complete before moving to the next line of code, the user interface becomes unresponsive or blocked until the task is completed. Async programming solves this by allowing the program to execute other tasks while waiting for the result of a long-running operation.

Why Use async and await

1. Improved Responsiveness: Keeps the user interface responsive by allowing other tasks to execute while waiting for asynchronous tasks to complete.
2. Better Resource Utilization: Helps in better resource management by freeing up threads, which can then handle other requests.
3. Enhanced Scalability: With asynchronous code, the server can handle more connections and requests, thus improving scalability.

The async and await Keywords

• async: A modifier that indicates that a method (or lambda expression) involves asynchronous operations. It must be used to define a method as asynchronous.
• await: An operator that can only be used within an async method. It is used to pause the execution of the method until the awaited task is completed.

Asynchronous Methods in ASP.NET MVC

In ASP.NET MVC, asynchronous methods are commonly used in controller actions to handle database operations, network calls, or I/O operations. Here's a detailed step-by-step example to help you understand how to use async and await in an MVC application.

Step-by-Step Example

Step 1: Create an MVC Application

First, create a new ASP.NET MVC application in Visual Studio. You can do this by going to File > New > Project > ASP.NET Web Application (.NET Framework), and then select MVC.

Step 2: Set Up the Model

Create a simple model that represents the data you want to work with. For this example, let's create a Product model:

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

Step 3: Set Up the Database Context

Next, set up a database context. We’ll use Entity Framework to handle database operations. Create a DbContext class:

using System.Data.Entity;

public class ProductContext : DbContext
{
    public DbSet<Product> Products { get; set; }
}

Step 4: Create the Controller

Create a controller to handle HTTP requests. For this example, we'll create a ProductController. This controller will have methods to display a list of products and to get product details.

using System.Threading.Tasks;
using System.Web.Mvc;

public class ProductController : Controller
{
    private readonly ProductContext _context = new ProductContext();
    
    // GET: Product
    public async Task<ActionResult> Index()
    {
        var products = await _context.Products.ToListAsync();
        return View(products);
    }

    // GET: Product/Details/5
    public async Task<ActionResult> Details(int? id)
    {
        if (id == null)
        {
            return new HttpStatusCodeResult(HttpStatusCode.BadRequest);
        }
        Product product = await _context.Products.FindAsync(id);
        if (product == null)
        {
            return HttpNotFound();
        }
        return View(product);
    }

    // GET: Product/Create
    public ActionResult Create()
    {
        return View();
    }

    // POST: Product/Create
    [HttpPost]
    [ValidateAntiForgeryToken]
    public async Task<ActionResult> Create([Bind(Include = "Id,Name,Description,Price")] Product product)
    {
        if (ModelState.IsValid)
        {
            _context.Products.Add(product);
            await _context.SaveChangesAsync();
            return RedirectToAction("Index");
        }

        return View(product);
    }
}

Step 5: Create Views

For each action method, create the corresponding views. Here’s how you can create the Index view.

Index.cshtml

@model IEnumerable<Product>

@{
    ViewBag.Title = "Products";
}

<h2>Products</h2>

<p>
    @Html.ActionLink("Create New", "Create")
</p>
<table class="table">
    <tr>
        <th>
            @Html.DisplayNameFor(model => model.Name)
        </th>
        <th>
            @Html.DisplayNameFor(model => model.Description)
        </th>
        <th>
            @Html.DisplayNameFor(model => model.Price)
        </th>
        <th></th>
    </tr>

@foreach (var item in Model) {
    <tr>
        <td>
            @Html.DisplayFor(modelItem => item.Name)
        </td>
        <td>
            @Html.DisplayFor(modelItem => item.Description)
        </td>
        <td>
            @Html.DisplayFor(modelItem => item.Price)
        </td>
        <td>
            @Html.ActionLink("Details", "Details", new { id=item.Id }) |
            @Html.ActionLink("Delete", "Delete", new { id=item.Id })
        </td>
    </tr>
}

</table>

Create.cshtml

@model Product

@{
    ViewBag.Title = "Create";
}

<h2>Create</h2>

@using (Html.BeginForm()) 
{
    @Html.AntiForgeryToken()
    
    <div class="form-horizontal">
        <h4>Product</h4>
        <hr />
        @Html.ValidationSummary(true, "", new { @class = "text-danger" })
        @Html.HiddenFor(model => model.Id)

        <div class="form-group">
            @Html.LabelFor(model => model.Name, htmlAttributes: new { @class = "control-label col-md-2" })
            <div class="col-md-10">
                @Html.EditorFor(model => model.Name, new { htmlAttributes = new { @class = "form-control" } })
                @Html.ValidationMessageFor(model => model.Name, "", new { @class = "text-danger" })
            </div>
        </div>

        <div class="form-group">
            @Html.LabelFor(model => model.Description, htmlAttributes: new { @class = "control-label col-md-2" })
            <div class="col-md-10">
                @Html.EditorFor(model => model.Description, new { htmlAttributes = new { @class = "form-control" } })
                @Html.ValidationMessageFor(model => model.Description, "", new { @class = "text-danger" })
            </div>
        </div>

        <div class="form-group">
            @Html.LabelFor(model => model.Price, htmlAttributes: new { @class = "control-label col-md-2" })
            <div class="col-md-10">
                @Html.EditorFor(model => model.Price, new { htmlAttributes = new { @class = "form-control" } })
                @Html.ValidationMessageFor(model => model.Price, "", new { @class = "text-danger" })
            </div>
        </div>

        <div class="form-group">
            <div class="col-md-offset-2 col-md-10">
                <input type="submit" value="Create" class="btn btn-default" />
            </div>
        </div>
    </div>
}

<div>
    @Html.ActionLink("Back to List", "Index")
</div>

@section Scripts {
    @Scripts.Render("~/bundles/jqueryval")
}

Step 6: Set Up Database Initialization

Set up database initialization to initialize your database with seed data. Modify the Application_Start method in Global.asax to include database initialization:

protected void Application_Start()
{
    AreaRegistration.RegisterAllAreas();
    FilterConfig.RegisterGlobalFilters(GlobalFilters.Filters);
    RouteConfig.RegisterRoutes(RouteTable.Routes);
    BundleConfig.RegisterBundles(BundleTable.Bundles);

    Database.SetInitializer(new ProductInitializer());
}

And create an initializer class:

using System.Data.Entity;

public class ProductInitializer : DropCreateDatabaseIfModelChanges<ProductContext>
{
    protected override void Seed(ProductContext context)
    {
        var products = new List<Product>
        {
            new Product { Name = "Laptop", Description = "High-performance laptop", Price = 1200.0m },
            new Product { Name = "Smartphone", Description = "Latest generation smartphone", Price = 800.0m }
        };

        foreach (var product in products)
        {
            context.Products.Add(product);
        }

        context.SaveChanges();
    }
}

Understanding the Asynchronous Code

Now, let's delve deeper into how the asynchronous code works in the ProductController.

Asynchronous Index Method

public async Task<ActionResult> Index()
{
    var products = await _context.Products.ToListAsync();
    return View(products);
}

• Task: The method returns a Task<ActionResult>, which means it will return an ActionResult after completing the asynchronous operation.
• await: The await keyword is used to call the ToListAsync method asynchronously. While ToListAsync is running, the method is paused, and other work can be done.
• ToListAsync: This method retrieves all products from the Products table asynchronously.

Asynchronous Details Method

public async Task<ActionResult> Details(int? id)
{
    if (id == null)
    {
        return new HttpStatusCodeResult(HttpStatusCode.BadRequest);
    }
    Product product = await _context.Products.FindAsync(id);
    if (product == null)
    {
        return HttpNotFound();
    }
    return View(product);
}

• FindAsync: This method retrieves a product by its ID asynchronously.

Asynchronous Create Method

[HttpPost]
[ValidateAntiForgeryToken]
public async Task<ActionResult> Create([Bind(Include = "Id,Name,Description,Price")] Product product)
{
    if (ModelState.IsValid)
    {
        _context.Products.Add(product);
        await _context.SaveChangesAsync();
        return RedirectToAction("Index");
    }

    return View(product);
}

• SaveChangesAsync: This method saves changes to the database asynchronously.

Benefits of Asynchronous Programming in ASP.NET MVC

• Improved Responsiveness: End-users can continue interacting with the application while the server handles long-running operations.
• Better Resource Utilization: Threads that are not waiting for I/O operations can handle other requests, increasing throughput.
• Enhanced Scalability: An application can handle more requests at the same time, especially under heavy load, leading to better performance.

Conclusion

Asynchronous programming with async and await is a powerful feature in ASP.NET MVC that can significantly improve the performance and scalability of web applications. By using asynchronous methods, developers can ensure that long-running operations do not block the main thread, leading to a more responsive and efficient application. As you work with larger and more complex applications, understanding and implementing asynchronous programming will be crucial for maintaining high performance and user satisfaction.

Additional Tips

• Use async and await for I/O-bound and CPU-bound operations: Async/await is particularly useful for I/O-bound operations (like database calls, file operations, web service calls) rather than CPU-bound operations (like calculations).
• Avoid blocking calls within async methods: Always ensure that you use asynchronous counterparts of library methods wherever possible within an async method to avoid potential deadlocks.
• Test thoroughly: Asynchronous code can introduce subtle bugs that are hard to find and debug. Thoroughly test your asynchronous methods to ensure they behave as expected.

By following these steps and tips, you'll be well on your way to mastering asynchronous programming in ASP.NET MVC with async and await. Happy coding!