Entity Framework CodeFirst : Simple Migrations

Entity Framework CodeFirst : Simple Migrations

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When I change my model from let’s say

//Employee Entity
public class Employee
{
    public int Id { get; set; }
    public string FullName { get; set; }
}

to

//Employee Entity
public class Employee
{
    public int Id { get; set; }
    public string FullName { get; set; }
    public string Email { get; set; } //New
}

Then I find a trouble. Either I have to drop create the whole database using

Database.SetInitializer<HRContext>(new DropCreateDatabaseIfModelChanges<HRContext>());

or I need to do it manually. But this deletes everything. Who wants that? No one. So I left with an option of reflecting only changes. Now in EF CodeFirst we call it as Migrations. This can be very in-depth customizable. I would like to show you the most simple option and you can take to complex user-defined approach based on your business need.

Step1: Run this command to your Package Manager Console

PM> Enable-Migrations

And the output would look like

image

After this two files will be created in project under a new folder “Migrations”

image

Then we need a small change there in the file configuration

internal sealed class Configuration : DbMigrationsConfiguration<ConsoleApplication1.HRContext>
{

Would be changed to

public sealed class Configuration : DbMigrationsConfiguration<ConsoleApplication1.HRContext>
{

And

AutomaticMigrationsEnabled = false;

would change to

AutomaticMigrationsEnabled = true;

Now the new Database initializer would look like,

Database.SetInitializer<HRContext>(new MigrateDatabaseToLatestVersion<HRContext, Migrations.Configuration>());

So the complete code would look like

public class Employee
{
    public int Id { get; set; }
    public string FullName { get; set; }
    public string Email { get; set; } //New
}
public class HRContext : DbContext
{
    public DbSet<Employee> Emps { get; set; }
}
class Program
{
    static void Main(string[] args)
    {
        //Database.SetInitializer<HRContext>(new DropCreateDatabaseIfModelChanges<HRContext>());
        Database.SetInitializer<HRContext>(new MigrateDatabaseToLatestVersion<HRContext, Migrations.Configuration>());
        var emp = new Employee() { FullName = "Wriju Ghosh", Email = "some@contoso.com" };
        using (var ctx = new HRContext())
        {
            //This would get me the database information
            string strConnection = ctx.Database.Connection.ConnectionString;
            Console.WriteLine(strConnection);
            ctx.Emps.Add(emp);
            ctx.SaveChanges();
            foreach (var em in ctx.Emps)
            {
                Console.WriteLine(em.FullName);
                Console.WriteLine(em.Email==null?"null":em.Email);
            }
        }
    }
}

Namoskar!!!

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