Data Migration In MVC3 (Using EF.4.3)

问题:

I am doing data-migration for my project. But I have one question, for example: I have Book table with following fields:

ID  Name   Color

1   Java    red

2   MVC     blue

3   .Net    blue

I tried to change the name of field from "Color" to "BookColor" using Code First tech. But after migration the table looked like this:

ID  Name   BookColor

1   Java    null

2   MVC     null

3   .Net    null

I lost my field values. How can I make sure that all value are transfered?

I'm using Entity Framework with MVC3

EDIT This is my DBMigration Class:

public partial class AddCreative : DbMigration
{

    public override void Up()
    {
        AddColumn("Authors", "Names", c => c.String(maxLength: 4000));
        DropColumn("Authors", "Name");
    }


    public override void Down()
    {
        AddColumn("Authors", "Name", c => c.String(maxLength: 4000));
        DropColumn("Authors", "Names");
    }
}

I have changed Name to Names after changing (I lost my data in name field).

回答1:

I had no problems using the following:

First, setup the migrations:

PM> Enable-Migrations
PM> Add-Migration RenameBookColorColumn

Then we setup the migrations class to perform the rename:

public class RenameBookColorColumn : DbMigration
{
    public override void Up()
    {
        this.RenameColumn("Books", "Color", "BookColor");
    }
    public override void Down()
    {
        this.RenameColumn("Books", "BookColor", "Color");
    }
}

Next, make a call to Update-Database so we can perform the changes:

PM> Update-Database -Verbose
Using NuGet project 'Example'.
Using StartUp project 'ExampleTest'.
Target database is: 'ExampleContext' (DataSource: .\SQLEXPRESS, Provider: System.Data.SqlClient, Origin: Convention).
Applying explicit migrations: [201207051400010_RenameBookColorColumn].
Applying explicit migration: 201207051400010_RenameBookColorColumn.
EXECUTE sp_rename @objname = N'Books.Color', @newname = N'BookColor',
@objtype = N'COLUMN' [Inserting migration history record]

And voila, it's renamed and the data is retained.

回答2:

You can work around the limitation by using the following code.

public partial class AddCreative : DbMigration
{
    public override void Up()
    {
        AddColumn("Authors", "Names", c => c.String(maxLength: 4000));
        Sql("UPDATE [Authors] SET [Names] = [Name]");
        DropColumn("Authors", "Name");
    }

    public override void Down()
    {
        AddColumn("Authors", "Name", c => c.String(maxLength: 4000));
        Sql("UPDATE [Authors] SET [Name] = [Names]");
        DropColumn("Authors", "Names");
    }
}