使用EF Code-first和迁移的专有ID值

Question

I develop my ASP.NET MVC4 app using EF Code-first, also im using Migrations feature. I have specific entity and i want to set explicit id values for some reasons. How can i do this? I tried to mark id property with attribute like this:

public class NewsSource
{
    [Key, DatabaseGenerated(DatabaseGeneratedOption.None)]
    public int Id { get; set; }

    public string Title { get; set; }

    public string WebSiteUrl { get; set; }
}

Then i add corresponding migration, delete database and try to update database using Seed() method like this:

context.NewsSources.AddOrUpdate(x => x.Title,
            new NewsSource {Id = 654, Title = "ABC", WebSiteUrl = @"http://www.abc.com/"},
            new NewsSource {Id = 22, Title = "XYZ", WebSiteUrl = @"http://XYZ.ru/"});

And ive got this error: "Cannot insert explicit value for identity column in table 'NewsSources' when IDENTITY_INSERT is set to OFF". How can i set identity_insert to ON using EF and migrations. As i understood from many topics its impossible and i have to use direct SQL-commands. Am i wrong?

Answer 1

I had a problem when I tried to change a column to an IDENTITY field when it was originally not an identity field. See this question and this one . You have to remove the column and recreate it to remove IDENTITY so fixing up foreign keys etc is probably a step too far for Entity Framework to do in a migration. You will have to alter the Up() and Down() methods yourself, or you may get away with doing it in the database.

Answer 2

What happens if you remove the DatabaseGenerated attribute and just leave the [Key] attribute?

public class NewsSource
{
    [Key]
    public int Id { get; set; }
    public string Title { get; set; }
    public string WebSiteUrl { get; set; }
}

I ran into this issue awhile back and I believe this was a work around for me. I can't test it now since I don't have any projects in front of me with EF in them. All I can say is EF code first and the nuget migrations package is a great thing, if you treat it the way you are supposed to treat it. I have gotten myself into a number of WTF moments when using the two together and trying to seed complex related models. Good luck!