Category: ASP.NET

Previous Episode: https://cuteprogramming.wordpress.com/2015/03/01/journey-to-asp-net-mvc-5/

I first said hi to ASP .NET MVC in the beginning of this year. On 28th January, I attended the .NET Developers Singapore meetup and listened to Nguyen Quy Hy’s talk about ASP .NET MVC. After that, I have been learning ASP .NET MVC and applying this new knowledge in both my work and personal projects.

After 6 months of learning ASP .NET MVC, I decided to again write down some new things that I have learnt so far.

URL in ASP .NET MVC and Google Recommendation

According to Google recommendation on URLs, it’s good to have URLs to be as simple as possible and human-readable. This can be easily done with the default URL mapping in ASP .NET MVC. For example, the following code allows to have human-readable URL such as http://www.example.com/Ticket/Singapore-Airlines.

routes.MapRoute(
    name: "Customized",
    url: "Ticket/{airlineName}",
    defaults: new { controller = "Booking", action = "Details", airlineName = UrlParameter.Optional }
);

In addition, Google also encourages us to use hyphens instead of underscores in our URLs as punctuation to separate the words. However, by default, ASP .NET MVC doesn’t support hyphens. One of the easy solutions is to extend the MvcRouteHandler to automatically replace underscores with hyphens.

public class HyphenatedRouteHandler : MvcRouteHandler
{
    protected override IHttpHandler GetHttpHandler(RequestContext requestContext)
    {
        requestContext.RouteData.Values["controller"] =
        requestContext.RouteData.Values["controller"].ToString().Replace("-", "_");

        requestContext.RouteData.Values["action"] =
        requestContext.RouteData.Values["action"].ToString().Replace("-", "_");
 
        return base.GetHttpHandler(requestContext);
    }
}

Then in the RouteConfig.cs, we will replace the default route map to the following mapping.

routes.Add(
    new Route("{controller}/{action}/{id}",
    new RouteValueDictionary(
        new { controller = "Home", action = "Index", id = UrlParameter.Optional }),
        new HyphenatedRouteHandler())
);

By doing this, we can name our controllers and actions using underscores and then we set all the hyperlinks and links in sitemap to use hyphens.

There are actually many discussions about this online. I have listed below some of the online discussions that I found to be interesting.

1. Allow Dashes Within URLs using ASP.NET MVC 4
2. ASP .NET MVC Support for URL’s with Hyphens
3. Asp.Net MVC: How Do I Enable Dashes in My URLs?
4. Automate MVC Routing

MVC-ViewModel

Previously when I was working on WPF projects, I learnt the MVVM design pattern. So, it confused me when there was also a “View Model” in MVC. I thought with the use of View Model in ASP .NET MVC, I would be using MVVM too. It later turns out to be not the case.

In MVC, the View Model is only a class and is still considered part of the M (Model). The reason of having ViewModel is for the V (View) to have a single object to render. With the help of ViewModel, there won’t be too much of UI logic code in the V and thus the job of the V is just to render that single object. Finally, there will also be a cleaner separation of concerns.

Why is ViewModel able to provide the V a single object? This is because ViewModel can shape multiple entities from different data models into a single object.

public class CartViewModel
{
    ...

    public List<CartItems> items { get; set; }
 
    public UserProfile user { get; set; }
}

Besides, what I like about ViewModel is that it contains only fields that are needed in the V. Imagine the following model Song, we need to create a form to edit everything but the lyrics, what should we do?

Wait a minute. Why do we need to care about this? Can’t we just remove the Lyrics field from the edit form? Well, we can. However, generally we do not want to expose domain entities to the V.

If people manage to do a form post directly to your server, then they can add in the Lyrics field themselves and your server will happily accept the new Lyrics value. There will be a bigger problem if we are not talking about Lyrics, but something more critical, for example price, access rights, etc.

Please take note that the default model binder in ASP .NET MVC automatically binds all inbound properties.

The first simple solution is to use the bind attribute to indicate which properties to bind.

Edit([Bind(Include = "SongID,Title,Length")] Song song)

I don’t like this approach because it’s just a string. There are many mistakes can happen just because of having typo in a string.

So the second solution that I use often is creating a ViewModel which we can use to define only the fields that are needed in the edit form (V).

Same as M (Model), ViewModel also has validation rules using data annotation or IDataErrorInfo.

AutoMapper

By using ViewModel, we need to having mapping code to map between the view model and the domain model. However, writing mapping code is very troublesome especially when there are many properties involved.

Luckily, there is AutoMapper. AutoMapper performs object-object mapping by transforming an input object of one type into an output object of another type.

Mapper.CreateMap<Location, LocationViewModel>();

AutoMapper has a smart way to map the properties from view model and the domain model. If there is a property called “LocationName” in the domain model, AutoMapper will automatically map to a property with the same name “LocationName” in the view model.

Session, ViewData, ViewBag, and TempData

In my first e-commerce project which is using ASP .NET, Session is widely used. From small things like referral URL to huge cart table, all are stored in Session. Everyone in the team was satisfied with using Session until the day we realized we had to do load balancing.

There is a very interesting discussion on Stack Overflow about the use of Session in ASP .NET web applications. I like how one of them described Session as follows.

Fundamentally, session pollutes HTTP. It makes requests (often containing their own state) dependent on the internal state of the receiving server.

In the e-commerce project, we are using In-Process Session State. That means the session has “affinity” with the server. So in order to use load balancing in Microsoft Azure, we have to use Source IP Affinity to make sure the connections initiated from the same client computer goes to the same Datacenter IP endpoint. However, that will cause an imbalanced distribution of traffic load.

Another problem of using In-Process Session State is that once there is a restart on IIS or the server itself, the session variables stored on the server will be gone. Hence, for every deploy to the server, the customers will be automatically logged out from the e-commerce website.

Then you might wonder why we didn’t store session state in a database. Well, this won’t work because we store inserialisable objects in session variables, such as HtmlTable. Actually, there is another interesting mode for Session State, called StateServer. I will talk more about it in my another post about Azure load balancing.

When I was learning ASP .NET MVC in the beginning, I always found creating view model to be not intuitive. So, I used ViewBag and ViewData a lot. However, this caused headaches for code maintenance. Hence, in the end, I started to use ViewModel in MVC projects to provide better Separation of Concern and easily maintainable code. Nevertheless, I am still using ViewBag and ViewData to provide extra data from controller to view.

So what is ViewData? ViewData is a property allowing data to be passed from a controller to a view using a dynamic-bound dictionary API. In MVC3, a new dynamic property called ViewBag was introduced. ViewBag enables developers to use simpler syntax to do what ViewData can do. For example, instead of writing

ViewData["ErrorMessage"] = "Please enter your name";

, we can now write

 ViewBag.ErrorMessage = "Please enter your name";

.

ViewData and ViewBag help to pass data from a controller to a view. What if we want to pass data from a controller to another controller, i.e. redirection. Both ViewData and ViewBag will contain null values once the controller redirects. However, this is not the case for TempData.

There is one important feature in TempData is that anything stored in it will be discarded after it is accessed in the next request. So, it is useful to pass data from a controller to another controller. Unfortunately, TempData is backed by Session in ASP .NET MVC. So, we need to be careful when to use TempData as well and how it will behave in load balancing servers.

JsonResult

Sometimes, I need to return JSON-formatted content to the response. To do so, I will use JsonResult class, for example

[AllowCrossSiteJson]
public JsonResult GetAllMovies()
{
    Response.CacheControl = "no-cache";
    try
    {
        using (var db = new ApplicationDbContext())
        {
            var availableMovies = db.Movies.Where(m => m.Status).ToList();
            
            return Json(new 
            { 
                success = true, 
                data = availableMovies
            }, 
            JsonRequestBehavior.AllowGet);
        }
    }
    catch (Exception ex)
    {
        return Json(new 
        { 
            success = false, 
            message = ex.Message 
        }, 
        JsonRequestBehavior.AllowGet);
    }
}

There are a few new things here.

(1) [AllowCrossSiteJson]

This is my custom attribute to give access to requests coming from different domains. The following code shows how I define the class.

public class AllowCrossSiteJsonAttribute : ActionFilterAttribute
{
    public override void OnActionExecuting(ActionExecutingContext filterContext)
    {
        filterContext.RequestContext.HttpContext.Response.AddHeader(
            "Access-Control-Allow-Origin", "*");
       
        base.OnActionExecuting(filterContext);
    }
}

(2) Response.CacheControl = “no-cache”;

This is to prevent caching to the action. There is a great post on Stack Overflow which provides more alternatives to prevent caching.

(3) return Json()

This is to return an instance of the JsonResult class.

(4) success

If you are calling the GetAllMovies() through AJAX, probably you can do something as follows to check if there is any exception or error thrown.

$.ajax({
    url: '/GetAllMovies',
    success: function(data) {
        // No problem
    },
    error: function(XMLHttpRequest, textStatus, errorThrown) {
        var obj = JSON.parse(jqXHR.responseText);
        alert(obj.error);
    }
});

The error callback above will only be triggered when the server returns non-200 status code. I thus introduced another status field to tell the caller more info, for example an exception raised in C# code or any invalid value being passed to GetAllMovies method through AJAX. Hence, in the AJAX call, we just need to update it to

$.ajax({
    url: '/GetAllMovies',
    success: function(data) {
        if (data.success) {
            // No problem
        } else {
            alert(data.message);
        }
    },
    error: function(XMLHttpRequest, textStatus, errorThrown) {
        var obj = JSON.parse(jqXHR.responseText);
        alert(obj.error);
    }
});

(5) JsonRequestBehavior.AllowGet

To give permission to GET request for GetAllMovies method. This has thing to do with JSON Hijacking which will be discussed in my another post.

ActionResult

Other than JsonResult, there are many other ActionResult classes which represent the result of an action method and their respective helper methods.

Currently, I use the following frequently.

1. ViewResult and View: Render a view as a web page;
2. RedirectToRouteResult and RedirectToAction: Redirect to another action (TempData is normally used here);
3. JsonResult and Json: Explained above;
4. EmptyResult and null: Allow action method to return null.

Export Report to Excel

Two years ago, I wrote a post about how to export report to Excel in ASP .NET Web Form project. So, how do we export report to Excel in MVC project? There are two ways available.

First one can be done using normal ViewResult, as suggested in a discussion on Stack Overflow.

public ActionResult ExportToExcel()
{
    var sales = new System.Data.DataTable("Sales Report");
    sales.Columns.Add("col1", typeof(int));
    sales.Columns.Add("col2", typeof(string));

    sales.Rows.Add(1, "Sales 1");
    sales.Rows.Add(2, "Sales 2");
    sales.Rows.Add(3, "Sales 3");
    sales.Rows.Add(4, "Sales 4");

    var grid = new GridView();
    grid.DataSource = sales;
    grid.DataBind();

    Response.ClearContent();
    Response.Buffer = true;
    Response.AddHeader("content-disposition", "attachment; filename=Report.xls");
    Response.ContentType = "application/ms-excel";
    Response.Charset = "";
 
    StringWriter sw = new StringWriter();
    HtmlTextWriter htw = new HtmlTextWriter(sw);
    grid.RenderControl(htw);

    Response.Output.Write(sw.ToString());
    Response.Flush();
    Response.End();

    return View("Index");
}

Second way will be using FileResult, as suggested in another discussion thread on Stack Overflow. I simplified the code by removing the styling related codes.

public sealed class ExcelFileResult : FileResult
{
    private DataTable dtReport;

    public ExcelFileResult(DataTable dt) : base("application/ms-excel")
    {
        dtReport = dt;
    }

    protected override void  WriteFile(HttpResponseBase response)
    {
        // Create HtmlTextWriter
        StringWriter sw = new StringWriter();
        HtmlTextWriter tw = new HtmlTextWriter(sw);

        tw.RenderBeginTag(HtmlTextWriterTag.Table);

        // Create Header Row
        tw.RenderBeginTag(HtmlTextWriterTag.Tr);
        DataColumn col = null;
        for (int i = 0; i < dtReport.Columns.Count; i++)
        {
            col = dtReport.Columns[i];
            tw.RenderBeginTag(HtmlTextWriterTag.Th);
            tw.RenderBeginTag(HtmlTextWriterTag.Strong);
            tw.WriteLineNoTabs(col.ColumnName);
            tw.RenderEndTag();
            tw.RenderEndTag();
        }
        tw.RenderEndTag();

        // Create Data Rows
        foreach (DataRow row in dtReport.Rows)
        {
            tw.RenderBeginTag(HtmlTextWriterTag.Tr);
            for (int i = 0; i <= dtReport.Columns.Count - 1; i++)
            {
                tw.RenderBeginTag(HtmlTextWriterTag.Td);
                tw.WriteLineNoTabs(HttpUtility.HtmlEncode(row[i]));
                tw.RenderEndTag();
            }
            tw.RenderEndTag();
        }

        tw.RenderEndTag();

        // Write result to output-stream
        Stream outputStream = response.OutputStream;
        byte[] byteArray = Encoding.Default.GetBytes(sw.ToString());
        response.OutputStream.Write(byteArray, 0, byteArray.GetLength(0));
    }
}

To use the code above, we just need to do the following in our controller.

public ExcelFileResult ExportToExcel()
{
    ...
    ExcelFileResult actionResult = new ExcelFileResult(dtSales) 
    { 
        FileDownloadName = "Report.xls" 
    };

    return actionResult;
}

Sending Email

To send email from my MVC project, I have the following code to help me out. It can accept multiple attachments too. So I also use it to send email with report generated using the code above attached. =)

In the code below, I am using Amazon Simple Email Service (SES) SMTP.

public Task SendEmail(
    string sentTo, string sentCC, string sentBCC,  string subject, string body, 
    string[] attachments = null) 
{
    // Credentials:
    var credentialUserName = "<username provided by Amazon SES>;
    var sentFrom = "no-reply@mydomain.com";
    var pwd = "<password provided by Amazon SES>";

    // Configure the client:
    System.Net.Mail.SmtpClient client = 
        new System.Net.Mail.SmtpClient("email-smtp.us-west-2.amazonaws.com");
    client.Port = 25;
    client.DeliveryMethod = System.Net.Mail.SmtpDeliveryMethod.Network;
    client.UseDefaultCredentials = false;

    // Create the credentials:
    System.Net.NetworkCredential credentials = 
        new System.Net.NetworkCredential(credentialUserName, pwd);
    client.EnableSsl = true;
    client.Credentials = credentials;

    // Create the message:
    var mail = new System.Net.Mail.MailMessage(sentFrom, sentTo);
    string[] ccAccounts = sentCC.Split(new char[] { ';' }, StringSplitOptions.RemoveEmptyEntries);
 
    foreach (string ccEmail in additionalCcAccounts)
    {
        mail.CC.Add(ccEmail);
    }
    
    string[] bccAccounts = sentBCC.Split(new char[] { ';' }, StringSplitOptions.RemoveEmptyEntries);

    foreach (string bccEmail in additionalBccAccounts) 
    {
        mail.Bcc.Add(bccEmail); 
    }
    
    mail.Subject = subject;
    mail.Body = body;
    mail.IsBodyHtml = true;

    if (attachments != null) 
    {
        for (int i = 0; i < attachments.Length; i++)
        {
            mail.Attachments.Add(new System.Net.Mail.Attachment(attachments[i]));
        }
    }

    client.SendComplete += (s, e) => client.Dispose();
    return client.SendMailAsync(mail);
}

To send an email without attachment, I just need to do the following in action method.

var emailClient = new Email();
await emailClient.SendEmail(
    "to@mydomain.com", "cc1@mydomain.com;cc2@domain.com", "bcc@mydomain.com", 
    "Email Subject", "Email Body");

To send email with attachment, I will then use the following code.

string[] attachmentPaths = new string[1];

var reportServerPath = Server.MapPath("~/report");

attachmentPaths[0] = reportServerPath + "\\Report.xls";

var emailClient = new Email();
await emailClient.SendEmail(
    "admin@mydomain.com", "", "", 
    "Email Subject", "Email Body", attachmentPaths);

Yup, that’s all what I have learnt so far in my MVC projects. I know this post is very, very long. However, I am still new to MVC and thus I am happy to be able to share with you what I learn in the projects. Please correct me if you find anything wrong in the post. Thanks! =)

Summer 2015 Self-Learning Project

This article is part of my Self-Learning in this summer. To read the other topics in this project, please click here to visit the project overview page.