UserManager.CreateAsync does not generate Id

Question

I just upgraded my MVC 5 application (was previously MVC 3 with SimpleMembership) to ASP.NET Identity 2.0 and I can work with existing users, but when I execute the following to create a new user:

var user = new ApplicationUser();
//user.Id = db.Users.Max(u => u.Id) + 1;    //does not help
user.UserName = model.UserName;
user.Email = model.EMailAddress;
var result = await UserManager.CreateAsync(user, model.Password);

I get the following:

System.Data.Entity.Core.UpdateException: An error occurred while updating the entries. See the inner exception for details. ---> System.Data.SqlClient.SqlException: Cannot insert the value NULL into column 'Id', table 'MyDB.dbo.AspNetUsers'; column does not allow nulls. INSERT fails. The statement has been terminated.

Does anyone have an idea why this is happening?

This is my UserManager:

var manager = new ApplicationUserManager(new ApplicationUserStore(context.Get<MyDbContext>()));

manager.UserValidator = new UserValidator<ApplicationUser, int>(manager)
{
    AllowOnlyAlphanumericUserNames = false,
    RequireUniqueEmail = true
};

manager.PasswordValidator = new PasswordValidator
{
    RequiredLength = 6,
    RequireNonLetterOrDigit = false,
    RequireDigit = false,
    RequireLowercase = false,
    RequireUppercase = false,
};

manager.EmailService = new EmailService();

var dataProtectionProvider = options.DataProtectionProvider;
if (dataProtectionProvider != null)
{
    manager.UserTokenProvider = new DataProtectorTokenProvider<ApplicationUser, int>(dataProtectionProvider.Create("ASP.NET Identity"));
}

I use int keys for the users and roles, but I had the default string-keys before and there the Id was also not filled and I got a similar error.

Answer 1

I found the problem:
Because I changed the key from string to int the following migration was created:

AlterColumn("dbo.AspNetUsers", "Id", c => c.Int(nullable: false, identity: true));

There it correctly generated identity: true, BUT MSSQL can't convert an existing column to an identity column => the column became a "normal INT column".
Identity must then asume that the column is an identity column and inserts null as the key and expects the DB to generate the id => exception.

The solution was to revert back to my SimpleMembership DB from an old backup and directly convert it to ASP.NET Identity using the int-key when creating the AspNetUsers-table.

P.S.: But I still don't know why I had similar problems with string-keys, but I like the int-keys better anyhow...