Getting Started with Entity Framework 6 Code First using MVC 5


Create an MVC Web Application

Open Visual Studio and create a new C# Web project named "ContosoUniversity".

In the New ASP.NET Project dialog box select the MVC template.
If the Host in the cloud check box in the Microsoft Azure section is selected, clear it.
Click Change Authentication.

In the Change Authentication dialog box, select No Authentication, and then click OK. For this tutorial you won't be requiring users to log on or restricting access based on who's logged on.

Back in the New ASP.NET Project dialog box, click OK to create the project. 

Set Up the Site Style

A few simple changes will set up the site menu, layout, and home page.
Open Views\Shared\_Layout.cshtml, and make the following changes:
  • Change each occurrence of "My ASP.NET Application" and "Application name" to "Contoso University".
  • Add menu entries for Students, Courses, Instructors, and Departments, and delete the Contact entry.
The changes are highlighted.
<!DOCTYPE html>
<html>
<head>
    <meta charset="utf-8" />
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>@ViewBag.Title - Contoso University</title>
    @Styles.Render("~/Content/css")
    @Scripts.Render("~/bundles/modernizr")
</head>
<body>
    <div class="navbar navbar-inverse navbar-fixed-top">
        <div class="navbar-inner">
            <div class="container">
                <button type="button" class="btn btn-navbar" data-toggle="collapse" data-target=".nav-collapse">
                    <span class="icon-bar"></span>
                    <span class="icon-bar"></span>
                    <span class="icon-bar"></span>
                </button>
                @Html.ActionLink("Contoso University", "Index", "Home", null, new { @class = "brand" })
                <div class="nav-collapse collapse">
                    <ul class="nav">
                        <li>@Html.ActionLink("Home", "Index", "Home")</li>
                        <li>@Html.ActionLink("About", "About", "Home")</li>
                        <li>@Html.ActionLink("Students", "Index", "Student")</li>
                        <li>@Html.ActionLink("Courses", "Index", "Course")</li>
                        <li>@Html.ActionLink("Instructors", "Index", "Instructor")</li>
                        <li>@Html.ActionLink("Departments", "Index", "Department")</li>
                    </ul>
                </div>
            </div>
        </div>
    </div>

    <div class="container">
        @RenderBody()
        <hr />
        <footer>
            <p>&copy; @DateTime.Now.Year - Contoso University</p>
        </footer>
    </div>

    @Scripts.Render("~/bundles/jquery")
    @Scripts.Render("~/bundles/bootstrap")
    @RenderSection("scripts", required: false)
</body>
</html>
In Views\Home\Index.cshtml, replace the contents of the file with the following code to replace the text about ASP.NET and MVC with text about this application:
@{
    ViewBag.Title = "Home Page";
}

<div class="jumbotron">
    <h1>Contoso University</h1>
</div>
<div class="row">
    <div class="col-md-4">
        <h2>Welcome to Contoso University</h2>
        <p>Contoso University is a sample application that
        demonstrates how to use Entity Framework 6 in an 
        ASP.NET MVC 5 web application.</p>
    </div>
    <div class="col-md-4">
        <h2>Build it from scratch</h2>
        <p>You can build the application by following the steps in the tutorial series on the ASP.NET site.</p>
        <p><a class="btn btn-default" href="http://www.asp.net/mvc/tutorials/getting-started-with-ef-using-mvc/">See the tutorial &raquo;</a></p>
    </div>
    <div class="col-md-4">
        <h2>Download it</h2>
        <p>You can download the completed project from the Microsoft Code Gallery.</p>
        <p><a class="btn btn-default" href="http://code.msdn.microsoft.com/ASPNET-MVC-Application-b01a9fe8">Download &raquo;</a></p>
    </div>
</div>
Press CTRL+F5 to run the site. You see the home page with the main menu.

Install Entity Framework 6

From the Tools menu click Library Package Manager and then click Package Manager Console.
In the Package Manager Console window enter the following command:
Install-Package EntityFramework
The image shows 6.0.0 being installed, but NuGet will install the latest version of Entity Framework (excluding pre-release versions), which as of the most recent update to the tutorial is 6.1.1.
This step is one of a few steps that this tutorial has you do manually, but which could have been done automatically by the ASP.NET MVC scaffolding feature. You're doing them manually so that you can see the steps required to use the Entity Framework. You'll use scaffolding later to create the MVC controller and views. An alternative is to let scaffolding automatically install the EF NuGet package, create the database context class, and create the connection string. When you're ready to do it that way, all you have to do is skip those steps and scaffold your MVC controller after you create your entity classes. 

Create the Data Model

Next you'll create entity classes for the Contoso University application. You'll start with the following three entities:
There's a one-to-many relationship between Student and Enrollment entities, and there's a one-to-many relationship between Course and Enrollment entities. In other words, a student can be enrolled in any number of courses, and a course can have any number of students enrolled in it.
In the following sections you'll create a class for each one of these entities.
Note If you try to compile the project before you finish creating all of these entity classes, you'll get compiler errors.

The Student Entity


In the Models folder, create a class file named Student.cs and replace the template code with the following code:
using System;
using System.Collections.Generic;

namespace ContosoUniversity.Models
{
    public class Student
    {
        public int ID { get; set; }
        public string LastName { get; set; }
        public string FirstMidName { get; set; }
        public DateTime EnrollmentDate { get; set; }
        
        public virtual ICollection<Enrollment> Enrollments { get; set; }
    }
}
The ID property will become the primary key column of the database table that corresponds to this class. By default, the Entity Framework interprets a property that's named ID or classnameID as the primary key.
The Enrollments property is a navigation property. Navigation properties hold other entities that are related to this entity. In this case, the Enrollments property of a Student entity will hold all of the Enrollment entities that are related to that Student entity. In other words, if a given Student row in the database has two related Enrollmentrows (rows that contain that student's primary key value in their StudentID foreign key column), that Studententity's Enrollments navigation property will contain those two Enrollment entities.
Navigation properties are typically defined as virtual so that they can take advantage of certain Entity Framework functionality such as lazy loading. (Lazy loading will be explained later, in the Reading Related Data tutorial later in this series.)
If a navigation property can hold multiple entities (as in many-to-many or one-to-many relationships), its type must be a list in which entries can be added, deleted, and updated, such as ICollection.

The Enrollment Entity


In the Models folder, create Enrollment.cs and replace the existing code with the following code:
namespace ContosoUniversity.Models
{
    public enum Grade
    {
        A, B, C, D, F
    }

    public class Enrollment
    {
        public int EnrollmentID { get; set; }
        public int CourseID { get; set; }
        public int StudentID { get; set; }
        public Grade? Grade { get; set; }
        
        public virtual Course Course { get; set; }
        public virtual Student Student { get; set; }
    }
}
The EnrollmentID property will be the primary key; this entity uses the classnameID pattern instead of ID by itself as you saw in the Student entity. Ordinarily you would choose one pattern and use it throughout your data model. Here, the variation illustrates that you can use either pattern. In a later tutorial, you'll you'll see how using ID withoutclassname makes it easier to implement inheritance in the data model.
The Grade property is an enum. The question mark after the Grade type declaration indicates that the Gradeproperty is nullable. A grade that's null is different from a zero grade — null means a grade isn't known or hasn't been assigned yet.
The StudentID property is a foreign key, and the corresponding navigation property is Student. An Enrollmententity is associated with one Student entity, so the property can only hold a single Student entity (unlike theStudent.Enrollments navigation property you saw earlier, which can hold multiple Enrollment entities).
The CourseID property is a foreign key, and the corresponding navigation property is Course. An Enrollmententity is associated with one Course entity.
Entity Framework interprets a property as a foreign key property if it's named <navigation property name><primary key property name> (for example, StudentID for the Student navigation property since the Student entity's primary key is ID). Foreign key properties can also be named the same simply <primary key property name> (for example, CourseID since the Course entity's primary key is CourseID).

The Course Entity


In the Models folder, create Course.cs, replacing the template code with the following code:
using System.Collections.Generic;
using System.ComponentModel.DataAnnotations.Schema;

namespace ContosoUniversity.Models
{
    public class Course
    {
        [DatabaseGenerated(DatabaseGeneratedOption.None)]
        public int CourseID { get; set; }
        public string Title { get; set; }
        public int Credits { get; set; }
        
        public virtual ICollection<Enrollment> Enrollments { get; set; }
    }
}
The Enrollments property is a navigation property. A Course entity can be related to any number of Enrollmententities.
We'll say more about the DatabaseGenerated attribute in a later tutorial in this series. Basically, this attribute lets you enter the primary key for the course rather than having the database generate it.

Create the Database Context

The main class that coordinates Entity Framework functionality for a given data model is the database context class. You create this class by deriving from the System.Data.Entity.DbContext class. In your code you specify which entities are included in the data model. You can also customize certain Entity Framework behavior. In this project, the class is named SchoolContext.
To create a folder in the ContosoUniversity project, right-click the project in Solution Explorer and click Add, and then click New Folder. Name the new folder DAL (for Data Access Layer). In that folder create a new class file namedSchoolContext.cs, and replace the template code with the following code:
using ContosoUniversity.Models;
using System.Data.Entity;
using System.Data.Entity.ModelConfiguration.Conventions;

namespace ContosoUniversity.DAL
{
    public class SchoolContext : DbContext
    {
    
        public SchoolContext() : base("SchoolContext")
        {
        }
        
        public DbSet<Student> Students { get; set; }
        public DbSet<Enrollment> Enrollments { get; set; }
        public DbSet<Course> Courses { get; set; }

        protected override void OnModelCreating(DbModelBuilder modelBuilder)
        {
            modelBuilder.Conventions.Remove<PluralizingTableNameConvention>();
        }
    }
}

Specifying entity sets

This code creates a DbSet property for each entity set. In Entity Framework terminology, an entity set typically corresponds to a database table, and an entity corresponds to a row in the table.
You could have omitted the DbSet<Enrollment> and DbSet<Course> statements and it would work the same. The Entity Framework would include them implicitly because the Student entity references the Enrollment entity and the Enrollment entity references the Course entity.

Specifying the connection string

The name of the connection string (which you'll add to the Web.config file later) is passed in to the constructor.
public SchoolContext() : base("SchoolContext")
{
}
You could also pass in the connection string itself instead of the name of one that is stored in the Web.config file. For more information about options for specifying the database to use, see Entity Framework - Connections and Models.
If you don't specify a connection string or the name of one explicitly, Entity Framework assumes that the connection string name is the same as the class name. The default connection string name in this example would then beSchoolContext, the same as what you're specifying explicitly.

Specifying singular table names

The modelBuilder.Conventions.Remove statement in the OnModelCreating method prevents table names from being pluralized. If you didn't do this, the generated tables in the database would be named StudentsCourses, and Enrollments. Instead, the table names will be StudentCourse, and Enrollment. Developers disagree about whether table names should be pluralized or not. This tutorial uses the singular form, but the important point is that you can select whichever form you prefer by including or omitting this line of code.

Set up EF to initialize the database with test data

The Entity Framework can automatically create (or drop and re-create) a database for you when the application runs. You can specify that this should be done every time your application runs or only when the model is out of sync with the existing database. You can also write a Seed method that the Entity Framework automatically calls after creating the database in order to populate it with test data.
The default behavior is to create a database only if it doesn't exist (and throw an exception if the model has changed and the database already exists). In this section you'll specify that the database should be dropped and re-created whenever the model changes. Dropping the database causes the loss of all your data. This is generally OK during development, because the Seed method will run when the database is re-created and will re-create your test data. But in production you generally don't want to lose all your data every time you need to change the database schema. Later you'll see how to handle model changes by using Code First Migrations to change the database schema instead of dropping and re-creating the database.
In the DAL folder, create a new class file named SchoolInitializer.cs and replace the template code with the
following code, which causes a database to be created when needed and loads test data into the new database.
using System;
using System.Collections.Generic;
using System.Linq;
using System.Web;
using System.Data.Entity;
using ContosoUniversity.Models;

namespace ContosoUniversity.DAL
{
    public class SchoolInitializer : System.Data.Entity. DropCreateDatabaseIfModelChanges<SchoolContext>
    {
        protected override void Seed(SchoolContext context)
        {
            var students = new List<Student>
            {
            new Student{FirstMidName="Carson",LastName="Alexander",EnrollmentDate=DateTime.Parse("2005-09-01")},
            new Student{FirstMidName="Meredith",LastName="Alonso",EnrollmentDate=DateTime.Parse("2002-09-01")},
            new Student{FirstMidName="Arturo",LastName="Anand",EnrollmentDate=DateTime.Parse("2003-09-01")},
            new Student{FirstMidName="Gytis",LastName="Barzdukas",EnrollmentDate=DateTime.Parse("2002-09-01")},
            new Student{FirstMidName="Yan",LastName="Li",EnrollmentDate=DateTime.Parse("2002-09-01")},
            new Student{FirstMidName="Peggy",LastName="Justice",EnrollmentDate=DateTime.Parse("2001-09-01")},
            new Student{FirstMidName="Laura",LastName="Norman",EnrollmentDate=DateTime.Parse("2003-09-01")},
            new Student{FirstMidName="Nino",LastName="Olivetto",EnrollmentDate=DateTime.Parse("2005-09-01")}
            };

            students.ForEach(s => context.Students.Add(s));
            context.SaveChanges();
            var courses = new List<Course>
            {
            new Course{CourseID=1050,Title="Chemistry",Credits=3,},
            new Course{CourseID=4022,Title="Microeconomics",Credits=3,},
            new Course{CourseID=4041,Title="Macroeconomics",Credits=3,},
            new Course{CourseID=1045,Title="Calculus",Credits=4,},
            new Course{CourseID=3141,Title="Trigonometry",Credits=4,},
            new Course{CourseID=2021,Title="Composition",Credits=3,},
            new Course{CourseID=2042,Title="Literature",Credits=4,}
            };
            courses.ForEach(s => context.Courses.Add(s));
            context.SaveChanges();
            var enrollments = new List<Enrollment>
            {
            new Enrollment{StudentID=1,CourseID=1050,Grade=Grade.A},
            new Enrollment{StudentID=1,CourseID=4022,Grade=Grade.C},
            new Enrollment{StudentID=1,CourseID=4041,Grade=Grade.B},
            new Enrollment{StudentID=2,CourseID=1045,Grade=Grade.B},
            new Enrollment{StudentID=2,CourseID=3141,Grade=Grade.F},
            new Enrollment{StudentID=2,CourseID=2021,Grade=Grade.F},
            new Enrollment{StudentID=3,CourseID=1050},
            new Enrollment{StudentID=4,CourseID=1050,},
            new Enrollment{StudentID=4,CourseID=4022,Grade=Grade.F},
            new Enrollment{StudentID=5,CourseID=4041,Grade=Grade.C},
            new Enrollment{StudentID=6,CourseID=1045},
            new Enrollment{StudentID=7,CourseID=3141,Grade=Grade.A},
            };
            enrollments.ForEach(s => context.Enrollments.Add(s));
            context.SaveChanges();
        }
    }
}
The Seed method takes the database context object as an input parameter, and the code in the method uses
that object to add new entities to the database. For each entity type, the code creates a collection of new
entities, adds them to the appropriate DbSet property, and then saves the changes to the database. It isn't
necessary to call the SaveChanges method after each group of entities, as is done here, but doing that helps
you locate the source of a problem if an exception occurs while the code is writing to the database.
To tell Entity Framework to use your initializer class, add an element to the entityFramework element in the application Web.config file (the one in the root project folder), as shown in the following example:
<entityFramework>
  <contexts>
    <context type="ContosoUniversity.DAL.SchoolContext, ContosoUniversity">
      <databaseInitializer type="ContosoUniversity.DAL.SchoolInitializer, ContosoUniversity" />
    </context>
  </contexts>
  <defaultConnectionFactory type="System.Data.Entity.Infrastructure.LocalDbConnectionFactory, EntityFramework">
    <parameters>
      <parameter value="v11.0" />
    </parameters>
  </defaultConnectionFactory>
  <providers>
    <provider invariantName="System.Data.SqlClient" type="System.Data.Entity.SqlServer.SqlProviderServices, EntityFramework.SqlServer" />
  </providers>
</entityFramework>
The context type specifies the fully qualified context class name and the assembly it's in, and thedatabaseinitializer type specifies the fully qualified name of the initializer class and the assembly it's in. (When you don't want EF to use the initializer, you can set an attribute on the context element:disableDatabaseInitialization="true".) For more information, see Entity Framework - Config File Settings.
As an alternative to setting the initializer in the Web.config file is to do it in code by adding aDatabase.SetInitializer statement to the Application_Start method in in the Global.asax.cs file. For more information, see Understanding Database Initializers in Entity Framework Code First.
The application is now set up so that when you access the database for the first time in a given run of the
application, the Entity Framework compares the database to the model (your SchoolContext and entity classes). If there's a difference, the application drops and re-creates the database.
Note: When you deploy an application to a production web server, you must remove or disable code that drops and re-creates the database. You'll do that in a later tutorial in this series.

Set up EF to use a SQL Server Express LocalDB database

LocalDB is a lightweight version of the SQL Server Express Database Engine. It's easy to install and configure, starts on demand, and runs in user mode. LocalDB runs in a special execution mode of SQL Server Express that enables you to work with databases as .mdf files. You can put LocalDB database files in the App_Data folder of a web project if you want to be able to copy the database with the project. The user instance feature in SQL Server Express also enables you to work with .mdf files, but the user instance feature is deprecated; therefore, LocalDB is recommended for working with .mdf files. In Visual Studio 2012 and later versions, LocalDB is installed by default with Visual Studio.
Typically SQL Server Express is not used for production web applications. LocalDB in particular is not recommended for production use with a web application because it is not designed to work with IIS.
In this tutorial you'll work with LocalDB. Open the application Web.config file and add a connectionStringselement preceding the appSettings element, as shown in the following example. (Make sure you update theWeb.config file in the root project folder. There's also a Web.config file is in the Views subfolder that you don't need to update.)
<connectionStrings>
    <add name="SchoolContext" connectionString="Data Source=(LocalDb)\v11.0;Initial Catalog=ContosoUniversity1;Integrated Security=SSPI;" providerName="System.Data.SqlClient"/>
</connectionStrings>
<appSettings>
  <add key="webpages:Version" value="3.0.0.0" />
  <add key="webpages:Enabled" value="false" />
  <add key="ClientValidationEnabled" value="true" />
  <add key="UnobtrusiveJavaScriptEnabled" value="true" />
</appSettings>
The connection string you've added specifies that Entity Framework will use a LocalDB database namedContosoUniversity1.mdf. (The database doesn't exist yet; EF will create it.) If you wanted the database to be created in your App_Data folder, you could add AttachDBFilename=|DataDirectory|\ContosoUniversity1.mdf to the connection string. For more information about connection strings, see SQL Server Connection Strings for ASP.NET Web Applications.
You don't actually have to have a connection string in the Web.config file. If you don't supply a connection string, Entity Framework will use a default one based on your context class. For more information, see Code First to a New Database.  

Creating a Student Controller and Views

Now you'll create a web page to display data, and the process of requesting the data will automatically trigger
the creation of the database. You'll begin by creating a new controller. But before you do that, build the project to make the model and context classes available to MVC controller scaffolding.
  1. Right-click the Controllers folder in Solution Explorer, select Add, and then click New Scaffolded Item.
  2. In the Add Scaffold dialog box, select MVC 5 Controller with views, using Entity Framework.
  3. In the Add Controller dialog box, make the following selections and then click Add:
    • Model class: Student (ContosoUniversity.Models). (If you don't see this option in the drop-down list, build the project and try again.)
    • Data context class: SchoolContext (ContosoUniversity.DAL).
    • Controller name: StudentController (not StudentsController).
    • Leave the default values for the other fields.   
    When you click Add, the scaffolder creates a StudentController.cs file and a set of views (.cshtml files) that work with the controller. In the future when you create projects that use Entity Framework you can also take advantage of some additional functionality of the scaffolder:  just create your first model class, don't create a connection string, and then in the Add Controller box specify new context class.  The scaffolder will create yourDbContext class and your connection string as well as the controller and views.
  4. Visual Studio opens the Controllers\StudentController.cs file. You see a class variable has been created that instantiates a database context object:
    private SchoolContext db = new SchoolContext();
    The Index action method gets a list of students from the Students entity set by reading the Students property of the database context instance:
     public ViewResult Index()
    {
        return View(db.Students.ToList());
    }
    The Student\Index.cshtml view displays this list in a table:
    <table>
        <tr>
            <th>
                @Html.DisplayNameFor(model => model.LastName)
            </th>
            <th>
                @Html.DisplayNameFor(model => model.FirstMidName)
            </th>
            <th>
                @Html.DisplayNameFor(model => model.EnrollmentDate)
            </th>
            <th></th>
        </tr>
    
    @foreach (var item in Model) {
        <tr>
            <td>
                @Html.DisplayFor(modelItem => item.LastName)
            </td>
            <td>
                @Html.DisplayFor(modelItem => item.FirstMidName)
            </td>
            <td>
                @Html.DisplayFor(modelItem => item.EnrollmentDate)
            </td>
            <td>
                @Html.ActionLink("Edit", "Edit", new { id=item.ID }) |
                @Html.ActionLink("Details", "Details", new { id=item.ID }) |
                @Html.ActionLink("Delete", "Delete", new { id=item.ID })
            </td>
        </tr>
    }
  5. Press CTRL+F5 to run the project. (If you get a "Cannot create Shadow Copy" error, close the browser and try again.)
    Click the Students tab to see the test data that the Seed method inserted. Depending on how narrow your browser window is, you'll see the Student tab link in the top address bar or you'll have to click the upper right corner to see the link.

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