Move property to new Entity in Entity Framework Co

问题:

I'm using Entity Framework Code First approach in my project. I have a problem with database migration.

Now I have the entity

public class Event
{
    public int Id { get; set; }
    public string Title { get; set; }
    public string City { get; set; }
}

I have already have data in my existing DataBase. Now I want to extend City property, like this

public class Event
{
    public int Id { get; set; }
    public string Title { get; set; }
    public virtual Location Location { get; set; }
}

so, City become to Location with many properties.

public partial class Location
{
    public int Id { get; set; }
    public string Country { get; set; }
    public string City{ get; set; }
    public string Address { get; set; }
    public string Place { get; set; }
}

So, I need for each row in Events Table create row in Locations Table and copy city. And set foreign key for event localtion to location row.But I don't know how to move existing data using Entity Framework Migration. I have read many post on Entity Framework Migration, but didn't find this case.

What is the best way to do this?

回答1:

You could do that in 3 steps

• Add Location
• Insert Location
• Drop City

Starting from

public class Event
{
    public int Id { get; set; }
    public string Title { get; set; }
    public string City { get; set; }
}

• Add Location property and class

• Add Location migration and update the database

  PM> Enable-Migrations

  PM> Add-Migration AddLocationTable

  PM> Update-Database

• Create empty migration for inserting the data

  PM> Add-Migration InsertLocationData

  The class should have empty Up and Down method. Add following code in the Up method.

  using (var context = new AppContext())
  {
      var events = context.Set<Event>().ToArray();
      foreach (var ev in events)
      {
          ev.Location = new Location { City = ev.City };
      }
      context.SaveChanges();
  }
  

• Run the migration again to apply InsertLocationData migration.

  PM> Update-Database

• Delete City property and run a migration to apply the changes.

  PM> Add-Migration DropCityFromEvent

  PM> Update-Database