A Step-by-Step Guide to Migrating a Project from ASP.NET MVC to ASP.NET Core

Step-by-step guide

Why porting to ASP.NET Core?

This is the second important characteristic that allows developers to integrate new features into their solution more flexible.

• Tag Helpers. Server-part code for participation in creating and rendering HTML elements in Razor files.
• View components. A new tool, similar to partial views, but of much higher performance. nopCommerce uses view components when reusing rendering logic is required and the task is too complex for partial view.
• DI in views. Although most of the data displayed in views comes from the controller, nopCommerce also has views where dependency injection is more convenient.

Migration

<Project Sdk="Microsoft.NET.Sdk">
  <PropertyGroup>
    <TargetFramework>netcoreapp2.2</TargetFramework>   
  </PropertyGroup>
  <ItemGroup>
    <PackageReference Include="Microsoft.AspNetCore.App" Version="2.2.6" />
    ...
  </ItemGroup>
  ...
</Project>

Startup

Startup

Startup

Configure

Configure

1. Configuring middleware for MVC and WebAPI requests
2. Configuring for: 

• Exception handling. You will inevitably face various collisions during porting, thus be ready and set up exception handling in the development environment. With UseDeveloperExceptionPage, we add middleware to catch exceptions.
• MVC routing. Registration of new routes has also been changed. IRouteBuilder is now used instead of RouteCollection, as a new way to register restrictions  (IActionConstraint)
• MVC/WebAPI filters. The filters should be updated in accordance with the new implementation of ASP.NET Core. 
• MVC/WebAPI Formatters
• Binding models

//add basic MVC feature
var mvcBuilder = services.AddMvc();

//add custom model binder provider (to the top of the provider list)
mvcBuilder.AddMvcOptions(options => options.ModelBinderProviders.Insert(0, new NopModelBinderProvider()));

/// <summary>
/// Represents model binder provider for the creating NopModelBinder
/// </summary>
public class NopModelBinderProvider : IModelBinderProvider
{
    /// <summary>
    /// Creates a nop model binder based on passed context
    /// </summary>
    /// <param name="context">Model binder provider context</param>
    /// <returns>Model binder</returns>
    public IModelBinder GetBinder(ModelBinderProviderContext context)
    {
        if (context == null)
            throw new ArgumentNullException(nameof(context));


        var modelType = context.Metadata.ModelType;
        if (!typeof(BaseNopModel).IsAssignableFrom(modelType))
            return null;

        //use NopModelBinder as a ComplexTypeModelBinder for BaseNopModel
        if (context.Metadata.IsComplexType && !context.Metadata.IsCollectionType)
        {
            //create binders for all model properties
            var propertyBinders = context.Metadata.Properties
                .ToDictionary(modelProperty => modelProperty, modelProperty => context.CreateBinder(modelProperty));
            
            return new NopModelBinder(propertyBinders, EngineContext.Current.Resolve<ILoggerFactory>());
        }

        //or return null to further search for a suitable binder
        return null;
    }
}

• Areas. To include Area in an ASP.NET Core app, add a regular route to the Startup.cs file. For example, this way it will look for configuring Admin/ area

app.UseMvc(routes => { routes.MapRoute("areaRoute", "{area:exists}/{controller=Admin}/{action=Index}/{id?}"); routes.MapRoute( name: "default", template: "{controller=Home}/{action=Index}/{id?}"); });

When doing it, the folder with the name Area with the Admin folder inside, should be in the app root. Now the attribute
[Area("Admin")] [Route("admin")].
will be used to connect the controller with this area.
It remains only to create views for all the actions described in the controller.

[Area("Admin")]
[Route("admin")]
public class AdminController : Controller
{    
    public IActionResult Index()
    {
        return View();
    }    
}

Validation
IFormCollection should not be passed to the controllers since in this case, asp.net server validation is disabled - MVC is suppressing further validation if the IFormCollection is found to be not null. To solve the problem, this property might be added to the model, this will prevent us from passing directly to the controller method.

This rule works only if a model is available, if there is no model, there will be no validation.

Child properties are no longer automatically validated and should be specified manually.
Step 6. Migrate HTTP handlers and HttpModules to Middleware
HTTP handlers and HTTP modules are in fact very similar to the concept of Middleware in ASP.NET Core, but unlike modules, the middleware order is based on the order in which they are inserted into the request pipeline. The order of modules is mainly based on the events of application life cycle. The order of middleware for responses is opposite to the order for requests, while the order of modules for requests and responses is the same. Knowing this, you can proceed with the update.
What should be updated:
• Migration of modules for Middleware (AuthenticationMiddleware, CultureMiddleware, etc.)
• Handlers to Middleware
• Use of new middleware
Authentication in nopCommerce does not use a built-in authentication system; for this purpose, AuthenticationMiddleware developed in accordance with the new ASP.NET Core structure is used.

public class AuthenticationMiddleware
{
   private readonly RequestDelegate _next;
   public AuthenticationMiddleware(IAuthenticationSchemeProvider schemes, RequestDelegate next)
   {
       Schemes = schemes ?? throw new ArgumentNullException(nameof(schemes));
       _next = next ?? throw new ArgumentNullException(nameof(next));
   }

   public IAuthenticationSchemeProvider Schemes { get; set; }
   
   public async Task Invoke(HttpContext context)
   {
       context.Features.Set<IAuthenticationFeature>(new AuthenticationFeature
       {
           OriginalPath = context.Request.Path,
           OriginalPathBase = context.Request.PathBase
       });
      
       var handlers = context.RequestServices.GetRequiredService<IAuthenticationHandlerProvider>();
       foreach (var scheme in await Schemes.GetRequestHandlerSchemesAsync())
       {
           try
           {
               if (await handlers.GetHandlerAsync(context, scheme.Name) is IAuthenticationRequestHandler handler && await handler.HandleRequestAsync())
                   return;
           }
           catch
           {
               // ignored
           }
       }

       var defaultAuthenticate = await Schemes.GetDefaultAuthenticateSchemeAsync();
       if (defaultAuthenticate != null)
       {
           var result = await context.AuthenticateAsync(defaultAuthenticate.Name);
           if (result?.Principal != null)
           {
               context.User = result.Principal;
           }
       }
       await _next(context);
   }
}

ASP.NET provides a lot of built-in middleware that you can use in your application, but the developer can also create his own middleware and add it to HTTP request pipeline.
To simplify this process, we added a special interface to nopCommerce, and now it’s enough to just create a class that implements it.

public interface INopStartup
{
    /// <summary>
    /// Add and configure any of the middleware
    /// </summary>
    /// <param name="services">Collection of service descriptors</param>
    /// <param name="configuration">Configuration of the application</param>
    void ConfigureServices(IServiceCollection services, IConfiguration configuration);

    /// <summary>
    /// Configure the using of added middleware
    /// </summary>
    /// <param name="application">Builder for configuring an application's request pipeline</param>
    void Configure(IApplicationBuilder application);

    /// <summary>
    /// Gets order of this startup configuration implementation
    /// </summary>
    int Order { get; }
}

Here you can add and configure your middleware:

/// <summary>
/// Represents object for the configuring authentication middleware on application startup
/// </summary>
public class AuthenticationStartup : INopStartup
{
    /// <summary>
    /// Add and configure any of the middleware
    /// </summary>
    /// <param name="services">Collection of service descriptors</param>
    /// <param name="configuration">Configuration of the application</param>
    public void ConfigureServices(IServiceCollection services, IConfiguration configuration)
    {
        //add data protection
        services.AddNopDataProtection();

        //add authentication
        services.AddNopAuthentication();
    }

    /// <summary>
    /// Configure the using of added middleware
    /// </summary>
    /// <param name="application">Builder for configuring an application's request pipeline</param>
    public void Configure(IApplicationBuilder application)
    {
        //configure authentication
        application.UseNopAuthentication();
    }

    /// <summary>
    /// Gets order of this startup configuration implementation
    /// </summary>
    public int Order => 500; //authentication should be loaded before MVC
}

Step 7. Using built-in DI
Dependency injection is one of the key features when designing an app in ASP.NET Core. You can develop loosely coupled applications that are more testable, modular and as a result more maintainable. This was made possible by following the principle of dependency inversion.
To inject dependencies, we used IoC (Inversion of Control) containers. In ASP.NET Core, such a container is represented by the IServiceProvider interface. Services are installed in the app in the Startup.ConfigureServices() method.
Any registered service can be configured with three scopes:
• transient
• scoped
• singleton

services.AddDbContext<ApplicationDbContext>(options =>
options.UseSqlServer(Configuration.GetConnectionString("DefaultConnection")));
services.AddSingleton<Isingleton,MySingleton>();

Step 8. Using WebAPI project compatibility shells (Shim)
To simplify migration of an existing Web API, we advise using the NuGet package  Microsoft.AspNetCore.Mvc.WebApiCompatShim. It supports the following compatible features:
• Adding ApiController type;
• Enabling web API style model binding;
• Extending model binding so that controller actions can accept HttpRequestMessage type parameters;
• Adding message formatters enabling actions to return results of HttpResponseMessage type.

services.AddMvc().AddWebApiConventions();

routes.MapWebApiRoute(name: "DefaultApi",
  	template: "api/{controller}/{id?}"
);

Step 9. Porting Application Configuration
Some settings were previously saved in the web.config file. Now we use a new approach based on the key-value pairs set by configuration providers. This is the recommended method in ASP.NET Core, and we use the appsettings.json file.
You can also use the NuGet package
System.Configuration.ConfigurationManager
if for some reason you want to continue using *.config. In this case, the app cannot run on Unix platforms, but on IIS only.
If you want to use the Azure key storage configuration provider, then you need to refer to Migrating content to Azure Key Vault. Our project did not contain such a task.
Step 10. Porting static content to wwwroot
To serve static content, specify to web host the content root of the current directory. The default is wwwroot. You can configure your folder for storing static files by setting up middleware.
Step 11. Porting EntityFramework to EF Core
If the project uses some specific features of Entity Framework 6, that are not supported in EF Core, it makes sense to run the application on the NET Framework. Though in this case, we will have to reject the multi-platform feature, and the application will run on Windows and IIS only. 
Below are the main changes to be considered:
• System.Data.Entity namespace is replaced by Microsoft.EntityFrameworkCore;
• The signature of the DbContext constructor has been changed. Now you should inject DbContextOptions;
• HasDatabaseGeneratedOption(DatabaseGeneratedOption.None) method is replaced by ValueGeneratedNever();
• WillCascadeOnDelete(false) method is replaced by OnDelete (DeleteBehavior.Restrict);
• OnModelCreating(DbModelBuilder modelBuilder) method is replaced by OnModelCreating(ModelBuilder modelBuilder);
• HasOptional method is no longer available;
• Object configuration is changed, now OnModelCreating is using since EntityTypeConfiguration is no longer available;
• ComplexType attribute is no longer available;
• IDbSet interface is replaced by DbSet;
• ComplexType - complex type support appeared in EF Core 2 with the Owned Entity type, and tables without Primary Key with QueryType in EF Core 2.1;
• External keys in EF Core generate shadow properties using the [Entity]Id template, unlike EF6, that uses the [Entity]_Id template. Therefore, add external keys as a regular property to the entity first;
• To support DI for DbContext, configure your DbContex in ConfigureServices.

/// <summary>
/// Register base object context
/// </summary>
/// <param name="services">Collection of service descriptors</param>
public static void AddNopObjectContext(this IServiceCollection services)
{
    services.AddDbContextPool<NopObjectContext>(optionsBuilder =>
    {
        optionsBuilder.UseSqlServerWithLazyLoading(services);
    });
}

/// <summary>
/// SQL Server specific extension method for Microsoft.EntityFrameworkCore.DbContextOptionsBuilder
/// </summary>
/// <param name="optionsBuilder">Database context options builder</param>
/// <param name="services">Collection of service descriptors</param>
public static void UseSqlServerWithLazyLoading(this DbContextOptionsBuilder optionsBuilder, IServiceCollection services)
{
    var nopConfig = services.BuildServiceProvider().GetRequiredService<NopConfig>();

    var dataSettings = DataSettingsManager.LoadSettings();
    if (!dataSettings?.IsValid ?? true)
        return;

    var dbContextOptionsBuilder = optionsBuilder.UseLazyLoadingProxies();

    if (nopConfig.UseRowNumberForPaging)
        dbContextOptionsBuilder.UseSqlServer(dataSettings.DataConnectionString, option => option.UseRowNumberForPaging());
    else
        dbContextOptionsBuilder.UseSqlServer(dataSettings.DataConnectionString);
}

To verify that EF Core generates a similar database structure as Entity Framework when migrating, use the  SQL Compare tool.

Step 12. Removing all HttpContext references and replacing obsolete classes and changing the namespace
During the project migration, you will find that a sufficiently large number of classes have been renamed or moved, and now you should comply with the new requirements. Here is a list of the main changes you may encounter:
• HttpPostedFileBase 🡪 FormFile
• Access HttpContext can now be accessed via IHttpContextAccessor
• HtmlHelper 🡪 HtmlHelper
• ActionResult 🡪 ActionResult
• HttpUtility 🡪 WebUtility
• ISession instead of HttpSessionStateBase accessible from HttpContext.Session. from Microsoft.AspNetCore.Http
• Request.Cookies returns IRequestCookieCollection: IEnumerable <KeyValuePair<string, string> >, then instead of HttpCookie we use KeyValuePair <string, string> from Microsoft.AspNetCore.Http
Namespace replacement:
• SelectList 🡪 Microsoft.AspNetCore.Mvc.Rendering
• UrlHelper 🡪 WebUtitlity
• MimeMapping 🡪 FileExtensionContentTypeProvider
• MvcHtmlString 🡪 IHtmlString and HtmlString
• ModelState, ModelStateDictionary, ModelError 🡪 Microsoft.AspNetCore.Mvc.ModelBinding
• FormCollection 🡪 IFormCollection
• Request.Url.Scheme 🡪 this.Url.ActionContext.HttpContext.Request.Scheme
Other:
• MvcHtmlString.IsNullOrEmpty(IHtmlString) 🡪 String.IsNullOrEmpty(variable.ToHtmlString())
• [ValidateInput (false)] - does not exist anymore and is no longer needed
• HttpUnauthorizedResult 🡪 UnauthorizedResult
• [AllowHtml] - directive does not exist anymore and is no longer needed
• TagBuilder.SetInnerText method is replaced by InnerHtml.AppendHtml
• JsonRequestBehavior.AllowGet when returning Json is no longer needed
• HttpUtility.JavaScriptStringEncode. JavaScriptEncoder.Default.Encode
• Request.RawUrl. Request.Path + Request.QueryString should be separately connected
• AllowHtmlAttribute - class no longer exists
• XmlDownloadResult - now you can use just return File(Encoding.UTF8.GetBytes (xml), "application / xml", "filename.xml");
•  [ValidateInput(false)] - directive does not exist anymore and is no longer needed
Step 13. Authentication and authorization update
As was already mentioned above, nopCommerce project does not involve the built-in authentication system, it is implemented in a separate middleware layer.
However, ASP.NET Core has its own system for credentials providing. You can view the documentation to know about them in details.
As for data protection, we no longer use MachineKey. Instead, we use the built-in data protection feature. By default, keys are generated when the application starts. As the data storage can be:
• File system - file system-based keystore
• Azure Storage - data protection keys in Azure BLOB object storage
• Redis - data protection keys in the Redis cache
• Registry - used if the application does not have access to the file system
• EF Core - keys are stored in the database
If the built-in providers are not suitable, you can specify your own key storage provider by making a custom IXmlRepository.
Step 14. JS/CSS update
The way of using static resources has changed, now they should all be stored in the root folder of the project wwwroot, unless other settings are made.
When using javascript built-in blocks, we recommend moving them to the end of the page. Just use the asp-location = "Footer" attribute for your <script> tags. The same rule applies to js files.
Use the BundlerMinifier extension as a replacement for System.Web.Optimization - this will enable bundling and minification. JavaScript and CSS while building the project (view the documentation).
Step 15. Porting views
First of all, Child Actions are no longer used, instead, ASP.NET Core suggests using a new high-performance tool - ViewComponents called asynchronously.
How to get a string from ViewComponent:

/// <summary>
/// Render component to string
/// </summary>
/// <param name="componentName">Component name</param>
/// <param name="arguments">Arguments</param>
/// <returns>Result</returns>
protected virtual string RenderViewComponentToString(string componentName, object arguments = null)
{   
    if (string.IsNullOrEmpty(componentName))
        throw new ArgumentNullException(nameof(componentName));

    var actionContextAccessor = HttpContext.RequestServices.GetService(typeof(IActionContextAccessor)) as IActionContextAccessor;
    if (actionContextAccessor == null)
        throw new Exception("IActionContextAccessor cannot be resolved");

    var context = actionContextAccessor.ActionContext;

    var viewComponentResult = ViewComponent(componentName, arguments);

    var viewData = ViewData;
    if (viewData == null)
    {
        throw new NotImplementedException();       
    }

    var tempData = TempData;
    if (tempData == null)
    {
        throw new NotImplementedException();       
    }

    using (var writer = new StringWriter())
    {
        var viewContext = new ViewContext(
            context,
            NullView.Instance,
            viewData,
            tempData,
            writer,
            new HtmlHelperOptions());

        // IViewComponentHelper is stateful, we want to make sure to retrieve it every time we need it.
        var viewComponentHelper = context.HttpContext.RequestServices.GetRequiredService<IViewComponentHelper>();
        (viewComponentHelper as IViewContextAware)?.Contextualize(viewContext);

        var result = viewComponentResult.ViewComponentType == null ? 
            viewComponentHelper.InvokeAsync(viewComponentResult.ViewComponentName, viewComponentResult.Arguments):
            viewComponentHelper.InvokeAsync(viewComponentResult.ViewComponentType, viewComponentResult.Arguments);

        result.Result.WriteTo(writer, HtmlEncoder.Default);
        return writer.ToString();
    }
}

Note that there is no need to use HtmlHelper anymore, ASP.NET Core includes many auxiliary built-in Tag Helpers. When the application is running, the Razor engine handles them on the server and ultimately converts to standard html elements.

This makes application development a whole lot easier. And of course, you can implement your own tag helpers.

We started using dependency injection in views instead of enabling settings and services using EngineContext.
So, the main points on porting views are as follows:
• Convert Views/web.config to Views/_ViewImports.cshtml - to import namespaces and inject dependencies. This file does not support other Razor features, such as function and section definitions
• Convert namespaces.add to @using
• Porting any settings to the main application configuration
• Scripts.Render and Styles.Render do not exist. Replace with links to output data of libman or BundlerMinifier

Conclusion

The process of migrating a large web application is a very time-consuming task which, as a rule, cannot be carried out without the pitfalls. We planned to migrate to a new framework as soon as its first stable version was released but were not able to make it right away, as there were some critical features that had not been transferred to .NET Core, in particular, those related to EntityFramework.
Therefore, we had first to make our release using a mixed approach - the .NET Core architecture with the .NET Framework dependencies, which in itself is a unique solution.

Being first is not easy, but we are sure we’ve made the right choice, and our huge community supported us in this.

We were able to fully adapt our project after the release of .NET Core 2.1, having by that time a stable solution already working on the new architecture. It remained only to replace some packages and rewrite the work with EF Core.
Thus, it took us several months and two released versions to completely migrate to the new framework. 
We can say with confidence that we are the first large project to carry out such a migration. In this guide, we tried to put together the entire migration process in a structured form and describe various bottlenecks so that other developers could rely on this material and follow the roadmap when solving the same task.