Getting Started With ASP.NET Core And Entity Framework Core

Entity Framework is an Object-Relational Mapper (ORM) that allows developers to work with a database using .NET objects. It eliminates the need for most of the data-access code that developers usually need to write. .NET Core comes with a new version of Entity Framework that is Entity Framework Core.

Pre Requests

Before staring the project, we must have the following configuration.

• Visual Studio 2015 Update 3
• .NET Core
• SQL Server Management Studio

If you already have all this configuration, then it is great; otherwise install all these prerequisites first.

Create an ASP.NET Core Application

Open Visual Studio and create a new ASP.NET Core project named as “EmployeeDetail”.

From templates section, select the “Web Application” template for the project and click on “Ok” button.

After successful creation of the project, you will get the following project structure.

Now, press “F5” and run the application. When we run this application, we will get the following output.

This is the default screen that we get in our application. But, we don’t need this default screen, so remove unnecessary code from “_layout” and “Index” views.

Now, go to “ _Layout” partial View and replace the content of page with the below code.

And also, replace the content of “Index” View with the following code.

After all the above changes, now our application will look like below.

Add Entity Framework Core Dependency

In our application, we will use SQL Server for the database, so we need to install the Entity Framework for SQL Server. To use SQL Server, the package is “Microsoft.EntityFrameworkCore.SqlServer”. Now, we need to add the configuration of Entity Framework in project.

Open your Project.json file and add the following lines under dependency section.

In next step, add the following line in “tools” section.

"Microsoft.EntityFrameworkCore.Tools" "1.0.0-preview2-final"

Create Entity Classes

After adding the dependencies for Entity Framework, let’s create Employee and Project entity classes. There will be many to one relationship b/w Employee and Project entity, that means one employee will handle only one project at a time but there can be more than one employees in a single project.

Employee Entity

Add an Employee class in Models folder and replace the code of Employee class with the following code.

In above code, EmployeeId property is primary key for the Employee entity and it is also identity type. The ProjectId is foreign key and corresponding navigation property is Project.

Project Entity

Now, add another class in Model folder and name this class as “Project”, replace the code of this class with following code.

The ProjectId property is primary key for this entity and other properties define the information about the project.

Add DbContext Class:

The main class of any Entity Framework structure is DbCntext class in this class we define all the entities that are used to create the table in the database. Now add another class in Model folder and named as “EmployeeContext”. This class will be derived from “System.Data.Entity.DbContext” class. Replace the code this class with following code.

In the above code, we defined two Dbset properties for Employee and Project class, this property will create two tables in database and name will be same as define in Dbset property.

Register Context with dependency Injection

After creating all entity and dbContext classes now we add a service for Entity Framework such that any component require this service can be provided by constructor. In our controller constructor we use this service to get the context instance. Now open “startup.cs” and add following code to “ConfigureServices” method.

In the above code we register a service for DbContext, here “DefaultConnection” providing the connection string that is defined in our “appsettings.json”. Now open your “appsettings.json” file and add following code. Replace the server name with your SQL Server name.

Add Migration and Create Database

After configuring dbContext and entity classes now we add the migration and using the “Update-Database” command we will create our project database. So first add the migration. Open your “Package Manager Console” run “Add-Migration firstMigration” command. This command will add the Migrations folder in your project and first file in Migrations folder contain all information how to create your database.

Now we will run “Update-Database” command, this command take codes available in migration class and updates your database. In our case this command create a “Employee” database in SQL Server that contains the all table and properties that we defined earlier in our model classes.

Now open your SQL Server, you will found that “Employee” database has been added.

Add initial data

Now our tables and database is ready let’s add some initials data into our tables.

Add Data into Project Table

Add Data into Employee Table

Now our database and application setup is ready, let’s start work on controllers and views section of application.

Employee List

After all the configuration is complete, now we start work on the view section of our project. First we create the Employee list and display some basic information of employees.

Add ViewModel

ViewModel in Asp.Net MVC is used to show only required information, ViewModel also used to show data from two or more models. Now we add a ViewModel folder in project. Add a new folder in project and named as “ViewModels”. After creating the “viewModels” folder, add a class in ViewModels folder. Right click on “ViewModels” folder and add a new class, named this class as “Employee_Project”. After creating the class now paste following code in this class.

In the above code we added four properties, values for first three property will be received from “Employee” model and value of fourth property will be received from the “Project” model.

Now go to “HomeController” and paste the following code in Index method.

In above lines of code we create an asynchronous method. Asynchronous programming is default mode of Asp.Net Core. Asynchronous programming provide a mechanism to write the code in non-blocking mode. A server has a limited numbers of threads, in high load situations if all the threads are blocked and a new request arrives on the server then result will be block and stop to respond. To overcome all these situations .Net core comes with an asynchronous programming method where we can write code for .Net Core MVC and EF core in an asynchronous way. Result will be a highly responsive and non-blocking server application. So during this project we will try to write the code in an asynchronous way.

In above code we use four keywords “async”, “Task<IActionResult>”, “await” and “ToListAsync”, all these keyword are used to make a method asynchronous.

• The “async” keyword is used to define a method as asynchronous, this keyword tells the compiler to generate callbacks for parts of the method body and to automatically create the Task<IActionResult> object that is returned. Here Task<IActionResult> define the return type of an asynchronous method as “IActionResult”
  
  
• The “await” keyword represents ongoing work, the asynchronous method in which await is used must be modified by the async keyword and “await” keyword tell the compiler to wait till the execution of an expression written in await.
  
  
• The “ToListAsync” keyword is an asynchronous version of “ToList” method and tries to execute the expression in an asynchronous way.

In the above code we create an asynchronous index method. In the first line of code “List<Employee_Project> ilIst” we create a list of “Employee_Project” ViewModel type. Using linq query we get “EmployeeId”, “EmployeeName”, “Designation”, “ProjectName” information about all employees and add these value in “iList” object using “ForEach” method. In the last line of code we returned this “iList” to view(return View(ilIst)).

After “Index” method in controller now open “Index” view and paste the following code in “Index” view.

In index view we get the “IEnumerable” object of “Employee_Project” ViewModel and create a list of all employees. For each employee entry we will add “Edit”,”Delete” and “Detail” option. Using “Edit” option we will redirect to a page where we can edit the information of employee, using “Delete” option we can delete any existing employee and using “Detail” option we can get all information about an employee. We also added an “Add Employee” button using that we can add a new employee entry. Code of Index method and Index view will create below screen.


Add New Employee

Home page of our application contains “Add Employee” button, on click of this button a new screen will open where we can add a new employee entry. Now create “NewEmployee” method in Home controller and paste the following code in this method.

In the above code we create an asynchronous method (NewEmployee), and in this method we are getting the list of all projects and return this list to “AddEmployee” view. On view page using this list we creates a dropdown list that contain name of all project. Now right click on View folder and add a new view , named this view as “AddEmployee”. Now paste following code in this view.