asp.net core (mvc) ViewModel requesting primary key

Question

While trying to scaffold a View from a ViewModel that contains fields from 2 models I need to update simultaneously, I keep getting an error that reads:

There was an error running the selected code generator: 'The entity type 'UserRegViewModel' requires a primary key to be defined.'

If I add the primary key

[Key]
public int Id { get; set; } 

to the ViewModel, a table in the DB with all the fields is created for the ViewModel, which I doubt is the correct usage of ViewModels.

My intention is to use the ViewModel to get a form from the view, and then in my controller, map each property from the VM to each of the domain models. I am successful in doing this manually (e.g. sending the ViewModel to the View, and getting the ViewModel back in the params of my HttpPost controller filled) if I leave the primary key declared, but I'm assuming I must be doing something wrong for this to be the case.

I believe I'm following all conventions (Independent folders for Models, Views, Controllers, ViewModels), and ViewModel called xxxxViewModel.cs inside the ViewModels folder.

EDIT: Full UserRegViewModel code:

using SERVICAPUY.Models.Business;
using System;
using System.Collections.Generic;
using System.ComponentModel.DataAnnotations;
using System.Linq;
using System.Threading.Tasks;


namespace SERVICAPUY.ViewModels
{
    public class UserRegViewModel
    {
        //[Key]
        //public int Id { get; set; }  // must be public!
                                     //public Usuario usuario { get; set; }
                                     //public IEnumerable<Prestamo> Prestamos { get; set; }

        //Usuario
        [Required(ErrorMessage = "El Nombre es obligatorio")]
        public string Nombre { get; set; }
        public string Cedula { get; set; }
        public string Direccion { get; set; }
        public string Direccion2 { get; set; }
        public string Ciudad { get; set; }
        public string Estado { get; set; }
        [Display(Name = "Código Postal")]
        public string CodPostal { get; set; }
        [Display(Name = "País")]
        public string Pais { get; set; }


        public string Telefono { get; set; }
        [DataType(DataType.Date)]
        public DateTime? FechaNacimiento { get; set; }

        //Prestamo
        public Auto auto { get; set; }

        [Required(ErrorMessage = "Cuántas cuotas son?")]
        [Range(1, 120, ErrorMessage = "El número de cuotas debe ser entre 1 y 120.")]
        public int Cuotas { get; set; }
        [Required(ErrorMessage = "Cuál es el monto del préstamo?")]
        public double Monto { get; set; }
        [Required(ErrorMessage = "Cuál es el interés?")]
        [Display(Name = "Interés")]
        public double? Interes { get; set; }
        [Required(ErrorMessage = "Qué día del mes le toca al usuario hacer el pago?")]
        [Display(Name = "Día de Pago")]
        [Range(1, 31, ErrorMessage = "El día de pago corresponde a día del mes.")]
        public int? DiaDePago { get; set; }
        [Display(Name ="Tipo de Prestamo")]
        public tipoPrestamo tipoPrestamo { get; set; }
        public Estatus Estatus { get; set; }
    }
}

Answer 1

@ZivWeissman found the answer. It's in the comments. There was a reference in the DbContext class to the ViewModel. Maybe that raises another question since I'm positive I didn't add the reference in there, but for now, the issue is resolved.