Code First Approach in Entity Framework

Introduction

Entity Framework is the Microsoft preferred method of data access for .NET applications. It supports strongly-typed access through LINQ. Entity Framework also allows developers to program against a conceptual model that reflects application logic rather than a relational model that reflects the database structure. Entity Framework can be used from an ASP.NET Application, (using Entity Data Source) or in ASP.NET MVC etc. In this article we will be creating this using MVC App and we’ll be using Visual Studio 2012 for demo.

What is Code First Approach?

Code First Approach provides an alternative to the Database First and Model First approaches to the Entity Data Model and creates database of us based on our classes that we will be creating in this article.

Demo MVC Application

Create a new ASP.NET MVC Project by New > Project > ASP.NET MVC 4 Web Application > Empty Template, you will get following structure.

Follow the steps for the rest part of this demo.

Step 1: Adding NuGet Package (if not available in references)

Right Click on the References Folder and select 'Manage NuGet Packages'. Alternatively you can install it from Tools > Library Package Manager > Package Manager Console and type 'Install-Package EntityFramework'. Okay, let's do this from NuGet Package window, type 'Entity Framework' in search box and click to install it. After installation you will notice a new library file in References Folder 'EntityFramework'.

Step 2: Adding Classes

Right click on the Models Folder to add a new class file named 'Student.cs' and type following codes.

using System;

using System.Collections.Generic;

using System.Linq;

using System.Web;

namespace Code_First_Approach_in_Entity_Framework.Models

{

    public class Student

    {

        public int StudentID { get; set; }

        public string Name { get; set; }

        public string Address { get; set; }

        public string Mobile { get; set; }

    }

}

So, I have declared four properties: StudentID, Name, Address and Mobile. Now go ahead and create a class to manage the link with the database above properties by inheriting DbContext. Note to use a namespace System.Data.Entity.

Step 2: Adding DbContext

Right click on the Models Folder to add a new class file named 'StudentContext.cs' and type following codes.

using System;

using System.Collections.Generic;

using System.Data.Entity;

using System.Linq;

using System.Web;

namespace Code_First_Approach_in_Entity_Framework.Models

{

    public class StudentContext : DbContext

    {

        public DbSet<Student> Students { get; set; }

    }

}

Now, this DbContext will do lots of things for us like it will create database and tables. You can check your newly added database file.

Step 3: Adding Controller and Views

Build the solution here by menu Build > Build Solution because I want Model class and Data context class to be popped up for me in Add Controller window. Go ahead to add a controller for this right click on the Controllers Folder in the Solution Explorer and select Add > Controller and use the name 'StudentController' and make following selections as given in image below.

Now, everything setup and ready for us including controller and its different views.

Let's run the project you will get error page as given below, this is because application is expecting 'Home' controller by default and we don't have this controller instead we have 'student' controller. You will see how to fix this in next step.

For now request 'student' controller using url something like http://localhost:portnumber/student and try to perform CRUD operation.

Everything is functioning well so far.

Step 4: Routing Application

When you run the application, you will get error page at very first hit, because the application is expecting 'Home' as a controller by default but we don't have 'Home' controller in our application instead we have 'Student' so we need to modify the default hit by the application. For this, find a file 'RouteConfig.cs' in 'App_Start' folder and make a single change.

routes.MapRoute(

    name: "Default",

    url: "{controller}/{action}/{id}",

    defaults: new { controller = "student", action = "Index", id = UrlParameter.Optional }

);

Just replaced the controller value to 'student'. Now run the application again, you will not see that error page anymore.

If you are interested to learn more on Routing, go ahead and learn it from ScottGu's blog post here http://weblogs.asp.net/scottgu/archive/2007/11/13/asp-net-mvc-framework-part-1.aspx or http://weblogs.asp.net/scottgu/archive/2007/12/03/asp-net-mvc-framework-part-2-url-routing.aspx.

Step 5: Data Validation Using Data Annotations

Assume, if you want to validate your data before sending it to database or you want to define any validation expression or want to make any field as 'Required'. For this we can take the advantage of 'System.ComponentModel.DataAnnotations.dll' assembly that is shipped with MVC package and you can find it in References folder. Now to enable the validation, open 'Student.cs' model and add some validation lines.

If you run the application here, you will get error message.

Because, this class file directly representing the database table's structure and making any changes here is subject of 'Code First Migrations' to update database and its tables and that why you got above error. Remember, you will lose all your records if you migrate your database here. Still Microsoft is working on this subject to avoid data lose, hoping to see such functionality in coming releases. Let's move to next step to do database migration.

If you want to learn more on 'Data Validation Using Data Annotations', please read here http://www.asp.net/mvc/tutorials/older-versions/models-(data)/validation-with-the-data-annotation-validators-cs.

Step 6: Database Migration

Now, don't worry about data lose here and go ahead to update the database table to test the above validation rules.

For this, open Global.asax file and make following changes.

You will notice above defined validations are working now, image give below.

If you want to learn more on 'Code First Database Migration', please read here http://blogs.msdn.com/b/adonet/archive/2012/02/09/ef-4-3-code-based-migrations-walkthrough.aspx.

Step 8: Looking at Database

So, now if you want to see that where the database have been created for this app. Open the directory where you have created your app and open App_Data folder you will find you database files.

Now the question is how to change the database instance name, this is soo long here. Let's learn it in next step.

Step 7: Change Database Name Instance

In above image you can see our default database name that is 'Code_First_Approach_in_Entity_Framework.Models.StudentContext'. Let's change it. Remember you will again lose your records.

Open 'StudentContext.cs' file and make following changes.

Now, again check back 'App_Data' folder, you will notice new database files have been created.

Download the source code from here.

Find a very nice video on this title by Julie Lerman here http://msdn.microsoft.com/en-us/data/gg715119.

I have done couple of video posts on MVC basics, if you are interested go and watch at my YouTube channel here http://www.youtube.com/user/abhimanyukumarvatsa.

Video Version of this post (in Hindi Language):-

I hope you like this post. Thanks.