EF 6 Code First migrations warn of or prevent destructive updates

Question

Question: Is there a setting to be warned of inadvertent loss of data when running a migration script.

I've been using code first migrations since 4.1, but while experimenting in a test project I ran into behavior I didn't expect. Maybe I haven't kept up on newer features.

Say I have a simple model:

    public class Customer
{
    public int Id { get; set; }
    public string Name { get; set; }
    public string Address { get; set; }
    public string City { get; set; }
}

and context:

    public class CustContext : DbContext
{
    public CustContext() : base("DefaultConnection") { }
    public DbSet<Customer> Customers { get; set; }
}

I've already enabled migrations, created the initial migration, updated the database as follows, then populated the table with data.

enable-migrations
add-migration initial
update-database

Then I changed the name of Address to HomeAddress. This is the migration script:

add-migration HomeAddress

    public partial class HomeAddress : DbMigration
{
    public override void Up()
    {
        AddColumn("dbo.Customers", "HomeAddress", c => c.String());
        DropColumn("dbo.Customers", "Address");
    }

    public override void Down()
    {
        AddColumn("dbo.Customers", "Address", c => c.String());
        DropColumn("dbo.Customers", "HomeAddress");
    }
}

This is the Configuration script:

    internal sealed class Configuration : DbMigrationsConfiguration<CodeFirstMigrations.Model1.CustContext>
{
    public Configuration()
    {
        AutomaticMigrationsEnabled = false;
        AutomaticMigrationDataLossAllowed = false;
    }

    protected override void Seed(CodeFirstMigrations.Model1.CustContext context)
    {

    }
}

When I ran the update-database command, I fully expected to get an error along the lines of "could not complete the migration because it would result in data loss..." I actually see that error a lot working on my own project.

But instead it happily dropped the (populated) Address column, and created a new column HomeAddress.

I figured there must be a configuration setting to control that behavior, but all I could find was AutomaticMigrationDataLossAllowed which apparently only applies to Automatic migrations.

Have I overlooked something?

Answer 1

This has been raised as an issue already but rejected as "by design".

Decided this is by design - we only warn for automatic migrations with data loss.

See the bug here.

Answer 2

You can use:

public partial class HomeAddress : DbMigration
{
    public override void Up()
    {
        AddColumn("dbo.Customers", "HomeAddress", c => c.String());
        Sql("UPDATE "dbo.Customers" SET HomeAddress = Address");
        DropColumn("dbo.Customers", "Address");
    }

    public override void Down()
    {
        AddColumn("dbo.Customers", "Address", c => c.String());
        DropColumn("dbo.Customers", "HomeAddress");
    }
}

Then you save your data.