How to Implement the Repository Pattern in ASP.NET MVC Application

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The Repository Pattern is one of the most popular patterns to create an enterprise level application. It restricts us to work directly with the data in the application and creates new layers for database operations, business logic and the application’s UI. If an application does not follow the Repository Pattern, it may have the following problems:

  • Duplicate database operations codes
  • Need of UI to unit test database operations and business logic
  • Need of External dependencies to unit test business logic
  • Difficult to implement database caching, etc.

Using the Repository Pattern has many advantages:

  • Your business logic can be unit tested without data access logic;
  • The database access code can be reused;
  • Your database access code is centrally managed so easy to implement any database access policies, like caching;
  • It’s easy to implement domain logics;
  • Your domain entities or business entities are strongly typed with annotations; and more.

On the internet, there are millions of articles written around Repository Pattern, but in this one we’re going to focus on how to implement it in an ASP.NET MVC Application. So let’s get started!

Project Structure

Let us start with creating the Project structure for the application. We are going to create four projects:

  1. Core Project
  2. Infrastructure Project
  3. Test Project
  4. MVC Project

Each project has its own purpose. You can probably guess by the projects’ names what they’ll contain: Core and Infrastructure projects are Class Libraries, Web project is a MVC project, and Test project is a Unit Test project. Eventually, the projects in the solution explorer will look as shown in the image below:

As we progress in this post, we will learn in detail about the purpose of each project, however, to start we can summarize the main objective of each project as the following:

So far our understanding for different projects is clear. Now let us go ahead and implement each project one by one. During the implementations, we will explore the responsibilities of each project in detail.

Core Project

In the core project, we keep the entities and the repository interfaces or the database operation interfaces. The core project contains information about the domain entities and the database operations required on the domain entities. In an ideal scenario, the core project should not have any dependencies on external libraries. It must not have any business logic, database operation codes etc.

In short, the core project should contain:

  • Domain entities
  • Repository interfaces or database operations interfaces on domain entities
  • Domain specific data annotations

The core project can NOT contain:

  • Any external libraries for database operations
  • Business logic
  • Database operations code

While creating the domain entities, we also need to make a decision on the restrictions on the domain entities properties, for example:

  • Whether a particular property is required or not. For instance, for a Product entity, the name of the product should be required property.
  • Whether a value of a particular property is in given range or not. For instance, for a Product entity, the price property should be in given range.
  • Whether the maximum length of a particular property should not be given value. For instance, for a Product entity, the name property value should be less than the maximum length.

here could be many such data annotations on the domain entities properties. There are two ways we can think about these data annotations:

  1. As part of the domain entities
  2. As part of the database operations logic

It is purely up to us how we see data annotations. If we consider them part of database operation then we can apply restrictions using database operation libraries API. We are going to use the Entity Framework for database operations in the Infrastructure project, so we can use Entity Framework Fluent API to annotate data.

If we consider them part of domain, then we can use System.ComponentModel.DataAnnotationslibrary to annotate the data. To use this, right click on the Core project’s Reference folder and click on Add Reference. From the Framework tab, selectSystem.ComponentModel.DataAnnotations and add to the project.

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How to Create a Custom Action Filter in ASP.NET MVC

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In ASP.NET MVC, Filters are used to inject logic at different levels of request processing and allow us to share logics across Controllers. For example, let’s say we want to run a security logic or a logging logic across the controller. To do so, we’ll write a filter containing those logics and enable them across all controllers. When we enable a filter across all controllers or actions, the filter enables the upcoming HTTP request.

Let us consider a scenario of Logging: for every incoming request, we need to log some data to the files on the basis of some logic. If we don’t create this logic inside a custom filter, then we will have to write logic for each controller’s action. This mechanism will lead to two problems:

  1. duplication of code; and
  2. violation of the Single Responsibility Principles; actions will now perform additional tasks of logging.

We can mitigate the problems above by putting the logging logics inside a custom action filter and applying the filter at all the controllers’ level.

Have you ever come across source code as shown in the image below? [Authorize] is an Authorization filter, and it gets executed before any HTPP request or Action method execution.  The Authorize filter is part of MVC, but if needed, we can create a custom filter too.

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Creating a photo album for ASP.NET MVC 5 Users using Azure BLOB storage

In this blog post, we will integrate ASP.NET MVC with Azure BLOB Storage by saving an image for an ASP.NET Identity 2.0 user in Azure BLOB Storage. We’re going to cover a lot of ground in this post, including:

  • Using ASP.NET Identity 2.0 user as reference in other table.
  • Creating a one to many relationship with ASP.NET Identity 2.0 user table
  • Connecting an ASP.NET MVC application to Azure Storage
  • Creating or Uploading a BLOB
  • Deleting a BLOB
  • Downloading a BLOB
  • Uploading a file from MVC form to a Azure BLOB

The final output of the blog post we plan on creating in this post will look more or less like the image below. As you can see, a user can upload a photo to her album, delete a photo, and of course, view photos too.

image

Architecture of the Application

The High-level architecture of the application can be drawn as shown in the image below:

image

Creating tables to save images

When we create an ASP.NET MVC application using the given MVC template in Visual Studio, by default, a basic authentication gets created using the ASP.NET Identity 2.0. In a default MVC project, a template for the authentication and authorization purpose ASP.NET Identity 2.0 creates the tables as shown in the image below:

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Creating Unit Tests for ASP.NET MVC Controllers

In this blog post, we will learn to write unit tests for various MVC controller’s behaviors, such as view’s return types, redirecting to different actions etc. Specifically, we’ll cover writing Unit Tests for:

  1. ViewData of the Controller
  2. TempData of the Controller
  3. ViewBag of the Controller
  4. View of the Controller

Let’s get started!

Creating the MVC Project under Test

Let us go ahead and create a MVC project under Test. To keep things simpler, I have selected ”No Authentication” for the project. In this example we are going to write unit tests for the HomeController. The HomeController contains two action methods:

  1. Index
  2. Details

We are going to write tests for these actions. The HomeController contains code as shown here:

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How to work with Enums in ASP.NET MVC

Recently I got a question from one of the readers that how to work with Enums in ASP.NET MVC? Before we move ahead in this post, let me tell you that it is very simple to work with Enums in ASP.NET MVC 5.1 and later. In MVC 5.1, HTML helper class EnumDropDownListFor has been introduced which is used to display the Enum in a dropdown as shown in the image below:

image

To start with let us consider that we have created an Enum TypeOfStudent as shown in the listing below. This Enum holds information about the type of a particular student.


public enum TypeOfStudent
    {
        [Display(Name = "Science Student.")]
        SS,
        [Display(Name = "Arts Student.")]
        AS,
        [Display(Name = "Economics Student.")]
        ES,

    }

We are going to use TypeOfStudent enum in the Student class which is created as shown in the listing below:


  public class Student
    {
        public int Id { get; set; }
        public string Name { get; set; }
        public int Age { get; set; }

        public TypeOfStudent StudentType { get; set;}
    }

Right click on the Controller folder and create a controller using the scaffolding. We need to select MVC 5 controller using the Entity Framework as shown in the image below:

image

In the Model class select Student and create a Data context class (perhaps select an existing one) to add a controller.

image

We just added a controller which is using Student class as model and the Student class has Enum TypeOfStudent as a property. Let us go ahead and run the application, we will find Enum property is rendered in the dropdown as shown in the image below:

image

As we see that Enum values has been populated in the StudentType dropdown. In the Create and Edit views of the controller, a control EnumDropDownListFor has been added as shown in the listing below:


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

When we create View using the scaffolding, MVC 5.1 and later use HTML Helper class EnumDropDownListFor to create dropdown from the Enum.

Using RadiButtons for the Enum

In MVC 5.1 onwards we do have support of EnumDropDownListFor which renders Enum values to a drop down. We may have a requirement to render the Enum values to RadioButton. There is no simple way to do it. For this we have to create HTML Helper class. Let us go ahead and create a HTML helper class. To create HTML Helper class

  1. Add a static class to the project
  2. Add HTML Helper method as static method to the class

I have created a folder named Helper and inside that created a class EnumRadioButtonHelper. Inside the static class, we have created static method EnumRadioButton to render Enums in the RadioButtons.


using System;
using System.Collections.Generic;
using System.ComponentModel.DataAnnotations;
using System.Linq;
using System.Linq.Expressions;
using System.Text;
using System.Threading.Tasks;
using System.Web;
using System.Web.Mvc;
using System.Web.Mvc.Html;

namespace MVCEnum.Helper
{
   public static class EnumRadioButtonHelper
    {
        public static MvcHtmlString EnumRadioButton<TModel, TProperty>(this HtmlHelper<TModel> htmlHelper, Expression<Func<TModel, TProperty>> expression)
        {
            var metaData = ModelMetadata.FromLambdaExpression(expression, htmlHelper.ViewData);

            var listOfValues = Enum.GetNames(metaData.ModelType);

            var sb = new StringBuilder();

            if (listOfValues != null)
            {
                sb = sb.AppendFormat("<ul>");

                
                foreach (var name in listOfValues)
                {
                    var label = name;

                    var memInfo = metaData.ModelType.GetMember(name);

                    if (memInfo != null)
                    {
                        var attributes = memInfo[0].GetCustomAttributes(typeof(DisplayAttribute), false);

                        if (attributes != null && attributes.Length > 0)
                            label = ((DisplayAttribute)attributes[0]).Name;
                    }

                    var id = string.Format(
                        "{0}_{1}_{2}",
                        htmlHelper.ViewData.TemplateInfo.HtmlFieldPrefix,
                        metaData.PropertyName,
                        name
                    );

                    var radio = htmlHelper.RadioButtonFor(expression, name, new { id = id }).ToHtmlString();

                    sb.AppendFormat("<li>{0}{1}</li>", radio, HttpUtility.HtmlEncode(label));
                }

                sb = sb.AppendFormat("</ul>");
            }

            return MvcHtmlString.Create(sb.ToString());
        }
    }
}

We can use the EnumRadioButton helper method on the view directly. We also need to make sure that, we have added the namespace of the helper class on the view. I have added the namespace as shown in the listing below:

@using MVCEnum.Helper
@model MVCEnum.Models.Student

Once namespace is added, EnumRadioButton can be used to render Enum in RadioButton as shown in the listing below:

  <div class="form-group">
            @Html.LabelFor(model => model.StudentType, htmlAttributes: new { @class = "control-label col-md-2" })
            <div class="col-md-10">            
                @Html.EnumRadioButton(m => m.StudentType)
            </div>
        </div>

On running the application, we will find StuentType is rendered in RadioButton also as shown in the image below:

image

We learnt how to work with Enums in MVC 5.1 and later. In MVC 5.1 EnumDropDownListFor has been introduced to render Enums in DropDown. We can also create HTML helper class to render Enums in RadioButtons. I hope you find this post useful. Thanks for reading.