Problem with customizing default identity in a MVC app.

    }

 public class Role : IdentityRole
    {
        public override Guid Id { get; set; }
        public string Discriminator { get; set; }
        
    }

public class UserRole : IdentityUserRole
    {
        public Guid Id {get; set;}
        public override Guid UserId { get; set; }
        public override Guid RoleId { get; set; }
    }

Then I start the application and check, if the Database is empty  => I seed an admin - create an user with new Guid for Id, then create and save Role with new Guid for RoleId, but after I try to create and add UserRole with the folowing code:

var userRole = new UserRole
                    {
                        Id = Guid.NewGuid(),
                        UserId = admin.Id,
                        RoleId = role.Id
                    };

....there comes this error:

"System.InvalidOperationException: 'The value of 'IdentityUserRole.UserId' is unknown when attempting to save changes. This is because the property is also part of a foreign key for which the principal entity in the relationship is not known.'"

Can anyone help me to solve this issue?