public partial class Car
{
    public Car()
    {
        this.CarCharacteristics = new HashSet<CarCharacteristic>();
    }
    
    public System.Guid Id { get; set; }
    public string Name { get; set; }
    public Nullable<int> Id_CarType { get; set; }
    
    public virtual ICollection<CarCharacteristic> CarCharacteristics { get; set; }
    public virtual CarType CarType { get; set; }
}

public partial class Car
{
    public int Id { get; set; }
    public Nullable<int> Id_CarType { get; set; }

    public virtual CarType CarType { get; set; }
}

public partial class Car
{
    #region Primitive Properties

    public virtual int Id
    {
        get;
        set;
    }

    public virtual Nullable<int> Id_CarType
    {
        get { return _id_CarType; }
        set
        {
            try
            {
                _settingFK = true;
                if (_id_CarType != value)
                {
                    if (CarType != null && CarType.Id != value)
                    {
                        CarType = null;
                    }
                    _id_CarType = value;
                }
            }
            finally
            {
                _settingFK = false;
            }
        }
    }
    private Nullable<int> _id_CarType;
    
    // и т. д.

public partial class Car
{
    public int Id { get; set; }
    public Nullable<int> Id_CarType { get; set; }

    public virtual CarType CarType { get; set; }
}