# IT:AD:EF/CodeFirst/Migrations:HowTo:Enable-Migrations #



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* See:
     * [[IT/AD/Code First/Migrations/HowTo/Add-Migration/Initial Migration]]


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<panel title="Summary">

Code Migrations have to be enabled on a project before it can start tracking changes.


</panel>


## Process ##


In `Nuget/Package Manager Console`, type:

<sxh Powershell>
Enable-Migrations -startupprojectname:App.AppHost.Web -projectname:App.Back.Infrastructure -EnableAutomaticMigrations=false
</sxh>

Note that in a single assembly POC, you could type:

<sxh Powershell>
    Enable-Migrations 

    //...which is the same as being verbose regarding EnableAutomaticMigrations:
    //Enable-Migrations -EnableAutomaticMigrations=false    
    
</sxh>


### New Migrations Folder

The `Enable-Migrations` [[IT/AD/Powershell/]] script creates a new `Migrations` folder in the [[IT/AD/Visual Studio/]] project.


### New Configuration File

The Migrations folder will contain a single `Configuration` class file:

<sxh csharp>
namespace XAct.Spikes.CodeMigration.Migrations
{
    using System;
    using System.Data.Entity;
    using System.Data.Entity.Migrations;
    using System.Linq;

    //Note: it's sealed, so has to be in same assembly as your app's Dbcontext
    internal sealed class Configuration : DbMigrationsConfiguration<XAct.Spikes.CodeMigration.MyContext>
    {
        public Configuration()
        {
            //Value set by flag when `Enable-Migrations` was invoked:
            AutomaticMigrationsEnabled = true;
        }

        protected override void Seed(XAct.Spikes.CodeMigration.MyContext context)
        {
            //  This method will be called after migrating to the latest version.

            //  You can use the DbSet<T>.AddOrUpdate() helper extension method 
            //  to avoid creating duplicate seed data. E.g.
            //
            //    context.People.AddOrUpdate(
            //      p => p.FullName,
            //      new Person { FullName = "Andrew Peters" },
            //      new Person { FullName = "Rowan Miller" }
            //    );
            //
        }
    }
}
</sxh>


### New Initial Migration

In addition -- depending on the value of `-EnableAutomaticMigrations` it make another file.

If `-EnableAutomaticMigrations` is set, no InitialCreate will be generated. But if it is not set, it will also make a new migration (eg, named `201309031323452_InitialCreate'), that will contain a complete description of the db up to that point...

>Note:
>if the db exists, and you invoke it with no flag, it will create the initializer -- but knowing that it will conflict/duplicate the existing db if run: *"Detected database created with a database initializer. Scaffolded migration '201309031323452_InitialCreate' corresponding to existing database. To use an automatic migration instead, delete the Migrations folder and re-run Enable-Migrations specifying the -EnableAutomaticMigrations parameter."*


If you want to start out with no code migrations, and no automated migrations, see this:

     * [[IT/AD/Code First/Migrations/HowTo/Add-Migration/Initial Migration]]


If a First Migration (InitialCreate) is created for you, it will look similar to:

<sxh csharp>
    public partial class InitialCreate : DbMigration
    {
        public override void Up()
        {
            CreateTable(
                "dbo.SomeEntities",
                c => new
                    {
                        Id = c.Int(nullable: false, identity: true),
                        Name = c.String(),
                    })
                .PrimaryKey(t => t.Id);
            
        }
        
        public override void Down()
        {
            DropTable("dbo.SomeEntities");
        }
    }
}
</sxh>


* See:
     * [[IT/AD/Code First/Migrations/HowTo/Add-Migration/Initial Migration]]



## Resources ##

* http://coding.abel.nu/2012/03/ef-migrations-command-reference/#Enable-Migrations