Why do the ASP.NET Identity interfaces use strings for primary and foreign keys?

Solution 1:

The intent was to allow both arbitrary id types (i.e. int, guid, string), but also avoid having serialization/casting issues for the id property.

So you can define your keys however you like and just implement the interface method

public class MyUser : IUser {
  public int Id { get; set; }
  string IUser.Id { get { return Id.ToString(); } }
}

Solution 2:

Adding to what Hao said:

1. The Identity runtime prefers strings for the user ID because we don’t want to be in the business of figuring out proper serialization of the user IDs (we use strings for claims as well for the same reason), e.g. all (or most) of the Identity interfaces refer to user ID as a string.
2. People that customize the persistence layer, e.g. the entity types, can choose whatever type they want for keys, but then they own providing us with a string representation of the keys.
3. By default we use the string representation of GUIDs for each new user, but that is just because it provides a very easy way for us to automatically generate unique IDs.

Solution 3:

With ASP.NET Core, you have a very simple way to specify the data type you want for Identity's models.

First step, override identity classes from < string> to < data type you want> :

public class ApplicationUser : IdentityUser<Guid>
{
}

public class ApplicationRole : IdentityRole<Guid>
{
}

Declare your database context, using your classes and the data type you want :

public class ApplicationDbContext : IdentityDbContext<ApplicationUser, ApplicationRole, Guid>
    {
        public ApplicationDbContext(DbContextOptions<ApplicationDbContext> options)
            : base(options)
        {
        }

        protected override void OnModelCreating(ModelBuilder builder)
        {
            base.OnModelCreating(builder);
            // Customize the ASP.NET Identity model and override the defaults if needed.
            // For example, you can rename the ASP.NET Identity table names and more.
            // Add your customizations after calling base.OnModelCreating(builder);
        }
    }

And in your startup class, declare the identity service using your models and declare the data type you want for the primary keys :

services.AddIdentity<ApplicationUser, ApplicationRole>()
            .AddEntityFrameworkStores<ApplicationDbContext, Guid>()
            .AddDefaultTokenProviders();

In ASP.NET identity tables, primary keys will still be in NVARCHAR but in your application it's will be the data type you want. You can check this in a controller :

    [HttpGet]
    public async Task<IActionResult> Test()
    {
        ApplicationUser user = await _userManager.GetUserAsync(HttpContext.User);
        Guid userId = user.Id; // No cast from string, it's a Guid data type
        throw new NotImplementedException();
    }