Performance in string filter queries vs foreign key

Question

I’m working on a project Asp.Net MVC 5 using code first and all entities have a property called UserId of the kind string. When I will make queries filtering by a certain user(Asp.Net Identity) I do so:

string currentUserId = User.Identity.GetUserId();
var products = await db.Products.Where(_ => _.UserId == currentUserId).ToListAsync();

I’m losing performance by not having a relationship through foreign key and just keeping the UserId on a property string?

Answer 1

I’m losing performance by not having a relationship through foreign key and just keeping the UserId on a property string?

It is. In fact, you can associate your ApplicationUser normally to any other entity, taking only a few precautions.

In order for the relationship between entities to work, care must be taken to envelop the context with the RoleManager and the UserManager as follows:

UserManager = new UserManager<ApplicationUser>(new UserStore<ApplicationUser>(context));
RoleManager = new RoleManager<IdentityRole>(new RoleStore<IdentityRole>(context));

In any case, if you feel you are experiencing a lot of performance loss, I suggest you reimplement your ApplicationUser using as key Guid or int:

public class MeuUserComGuid : IdentityUser<Guid, GuidUserLogin, GuidUserRole, GuidUserClaim>
{
    public User()
    {
        Id = Guid.NewGuid();
    }

    public User(string name) : this() { UserName = name; }

    public string FirstName { get; set; }
    public string LastName { get; set; }
}