Tuesday, 3 September 2013

Learning MVC Part 4 : Creating MVC Application with EntityFramework Code First Approach

Introduction

In our first three articles, we learnt a lot about MVC, starting from definition to use, from creating an application to connecting the MVC application with database using different techniques.
In the very last part of the series, we learnt how to connect our MVC application with existing database using Entity Framework.
This article will focus on connecting our MVC application with database using CodeFirst approach, i.e., one of the features Microsoft’s Entity Framework provides.

Our Roadmap

Just to remind our full roadmap towards learning MVC:


Pre-requisites

There are few pre-requisites before we start with the article:
  1. We have the running sample application that we created in the third part of the article series.
  2. We have EntityFramework 4.1 package or DLL on our local file system.
  3. We understand how MVC application is created.

Code-First Approach

To achieve a domain driven design, Entity Framework introduced EF 4.1 Code First. In the Code First approach, we focus on the domain design or entities/POCO classes first and create classes as per our model requirement. We do not have the database of the application, rather we create database automatically from code after defining our domain. The database created perfectly matches with the domain we design, so we have to be very conscious and keen in designing our domain model. It feels exciting to see database created on the fly with the help of our entities and XML configuration, without even opening database server.
No matter, you are not an expert in database, if you are a C# developer, just focus on your model/class creation.EntityFramework will take headache of creating and managing database for you.

Procedure

Step 1: Open the MVC application that we created in Learning MVC-Part3 in your Visual Studio.


We can clearly see and remember what we used to connect our MVC application to database with the help of entity framework, yes it was edmx class and our Model.tt classes generated from edmx classes.

Step 2: We don’t need the existing data-base, so you can delete the already created database for our part 3 application (if created).

Step 3: We don’t need edmx files now, so let’s clean our application, wipe out all these classes. Just deleteEFDataModel.edmxModel1.Context.tt and Model1.tt files. Now please do not run the application. It will give compile time errors, since we were using those classes ;-), Our solution will look like:


Our old solution had UserList class in Models folder, I have only changed the name of the class for differentiating it with previous application, and readability as was in the first part.

Step 4: As simple as that, just add a class to your solution, and name it MVCDBContext.cs as shown in the following image:


Step 5: Just add System.Data.Entity DLL as a reference to the solution if not already added.


Step 6: Use the namespace System.Data.Entity in our DBContext class, and inherit the added class fromDBContext class,

DbContext class: According to MSDN, DbContext class is conceptually similar to ObjectContext. To define, theObjectContext class is the part of the core EF API in the Microsoft .NET Framework 4 and this is our hero class that allows us to perform queries, change tracking and update the database using the strongly typed classes that represent our model (entity class). The DbContext is a wrapper around ObjectContext that exposes the most commonly used features of ObjectContext as well as provides some simpler “shortcuts” to tasks that are frequently used but complicated to code directly with ObjectContext. Simplfied alternative to ObjectContext and is the primary object for interacting with a database using a specific model.

Step 7: Add a DBSet property to the DbContext class that we created:
public DbSet<User> Users { get; set; }
User, defined in angular brackets, is the model that we created in Models folder, so our MVCDBContext class looks like:
using System;
using System.Collections.Generic;
using System.Data.Entity;
using System.Linq;
using System.Web;
using LearningMVC.Models;

namespace LearningMVC
{
    public class MVCDBContext : DbContext
    {
        public DbSet<User> Users { get; set; }
    }
}
That’s it, our 90% work is done?
DbSet property: It is a simplified alternative to ObjectSet and is used to perform CRUD operations against a specific type from the model.
By default, the name of the DbContext class will be the name our database that will automatically be created, so be wise to select the name of context class, else it could be handled in web.config as well.
The name of model will be the name of Table in database and properties of model will be the columns of the table.

Our Heroes

Both DbContext and DbSet are our super heroes, in creating and dealing with database operations, and make us far abstracted, providing ease of use to us.
When we are working with DbContext, we are in real working with entity sets. DbSet represents a typed entity set that is used to perform create, read, update, and delete operations. We are not creating DbSet objects and using them indepedently. DbSet can be only used with DbContext.

Step 8: Define a connection string in web.config file, you can remove previously defined connection string, the new connection string will somewhat look like:


The name of the connection string will be the name of the DbContect that we defined, i.e., MVCDbContext.

Step 9: Now, we just have to modify the access method in controllers, earlier, when we created application in third part, we were accessing the context class from the modelcontext class that was generated from edmx file. Edmx file was added having reference to already created database.
But now the case is different, we don’t have a database now, we’ll access the table and columns using ourMVCDBContext class in controllers, so just change the following line of code used in Actions of earlier application:
var dbContext = new MVCEntities() ;
to
var dbContext = new MVCDBContext();
Job done. 
Just Hit F5, and you’ll see:


How does the application run, where is the database??? Dude, go back to your database server, and check for database:


We see our database is created, with the name MVCDB, that’s the magic of EntityFramework. Now we can perform all the CRUD operations on this database, using our application. Just create a new user.


In database we see, user created.


By default, integer property with ID in its name of model will be the primary key in the database, in our caseUserId, or you can define the primary key in the model too.

Conclusion

Now we know how to play with EntityFramework to create database as per our domain model from our code, we have already moved ahead to advanced concepts of MVC and Entity Framework.


When we see the definition of DbContext, it uses the terms Repository Pattern and Unit of Work Pattern. We’ll discuss these more in detail in my next article.
For more informative articles,visit my blog A Practical Approach  
Happy coding! :-)

Share/Bookmark