পার্ট 3 - Entity Framework Code First Approach

আগের আর্টিকেলে বলেছিলাম Entity Framework supports
1. Database first or schema first approach - Discussed in Part 1
2. Model first approach - Discussed in Part 2
3. Code first approach - এই আর্টিকেলে

Entity Framework এর Code-first approach আমাদেরকে custom classes তৈরি করার সুযোগ দেয়, এবং পরবর্তীতে সেই custom classes গুলোর উপর basis করে automatically database generate করে। চলুন একটা example দিয়ে দেখা যাক। আমরা গত পর্বের যে Demo প্রোজেক্ট নিয়ে কাজ করছিলাম, এই আর্টিকেলে ঐ Demo প্রোজেক্টকেই Entity Framework এর Code-first approach এ modify করবো।

N.B: Entity Framework এর Code First Approach এর practical ধাপগুলো আমি আপনাদের বোঝার সুবিধার জন্য English এ explain করবো। এই step গুলো VS2017(Visual Studio 2017) এ execute করা হয়েছে।আর এই আর্টিকেলের explainations গুলো ভালভাবে বুঝতে অবশ্যই অবশ্যই নিচের এই Video টা একবার হলেও দেখে আসুন। ধন্যবাদ।। 

Step 1: Delete EmployeeModel.edmx && EmployeeModel.edmx.sql files from the solution explorer.

Step 2: Add a class file to the project. Name it Employee.cs. Copy and paste the following code.

public class Employee

{

    // Scalar Properties

    public int Id { get; set; }

    public string FirstName { get; set; }

    public string LastName { get; set; }

    public string Gender { get; set; }

    public int Salary { get; set; }

    // Navigation Property

    public Department Department { get; set; }

}

Step 3: Add a class file to the project. Name it Department.cs. Copy and paste the following code.

public class Department

{

    // Scalar Properties

    public int Id { get; set; }

    public string Name { get; set; }

    public string Location { get; set; }

    // Navigation Property

    public List<Employee> Employees { get; set; }

}

Step 4: Add a class file to the project. Name it EmployeeDBContext.cs. Copy and paste the following code.

// EmployeeDBContext class must inherit from DbContext

// present in System.Data.Entity namespace

public class EmployeeDBContext : DbContext

{

    public DbSet<Department> Departments { get; set; }

    public DbSet<Employee> Employees { get; set; }

}

Step 5: Add a class file to the project. Name it EmployeeRepository.cs. Copy and paste the following code.

public class EmployeeRepository

{

    public List<Department> GetDepartments()

    {

        EmployeeDBContext employeeDBContext = new EmployeeDBContext();

        return employeeDBContext.Departments.Include("Employees").ToList();

    }

}

Step 6: Add the database connection string in web.config file.

<connectionStrings>

  <add name="EmployeeDBContext"

       connectionString="server=.; database=Sample; integrated security=true;"

       providerName="System.Data.SqlClient"/>

</connectionStrings>

Please Note: If ProviderName is not specified the following runtime error will be thrown.

The connection string 'EmployeeDBContext' in the application's configuration file does not contain the required providerName attribute."

Step 7: Configure Object Data Source control
a) Delete EntityDataSource control, that is already there in WebForm1.aspx.
b) Drag and Drop ObjectDataSource control.
c) Right click on ObjectDataSource control and select "Show Smart Tag" option from the context menu
d) Click on "Configure Data Source..." link
e) On "Choose a Business Object" screen, select "EmployeeRepository" and click "Next"

Choose a Business Object

f) On "Define Data Methods" screen, select GetDepartments() method and click "Finish"

Step 8: Configure GridView control
a) Right click on GridView control and select "Show Smart Tag" option from the context menu
b) Select "ObjectDataSource1" from "Choose Data Source" drop-down list
c) Click "No" to "Refresh Fields and Keys for GridView1" when prompted

Step 9: Rebuild the solution.

Step 10: Delete the already existing database from SQL Server Management Studio.

Step 11: Run the application by pressing CTRL + F5. Notice that we don't have any data displayed on WebForm1. This is because we don't have any data in the Departments and Employees tables. At this point, we have the following created automatically.
a) Sample database
b) Departments table
c) Employees table

Step 12: Use the SQL script to populate the tables with data.

Insert into Departments values ('IT', 'New York')

Insert into Departments values ('HR', 'London')

Insert into Departments values ('Payroll', 'Sydney')

Insert into Employees values ('Mark', 'Hastings', 'Male', 60000, 1)

Insert into Employees values ('Steve', 'Pound', 'Male', 45000, 3)

Insert into Employees values ('Ben', 'Hoskins', 'Male', 70000, 1)

Insert into Employees values ('Philip', 'Hastings', 'Male', 45000, 2)

Insert into Employees values ('Mary', 'Lambeth', 'Female', 30000, 2)

Insert into Employees values ('Valarie', 'Vikings', 'Female', 35000, 3)

Insert into Employees values ('John', 'Stanmore', 'Male', 80000, 1)

Step 13: Refresh the Web Form and we should see the data as following...

Entity Framework Code First Approach Output