ValidateModel(u);

[DisplayFormat(DataFormatString = "{0:dd-MM-yyyy}", ApplyFormatInEditMode = true)]
    public DateTime FECHA_ADQ { get; set; }

foreach (var a in excel.Worksheet<ViewModel>(sheet.First())) {
    //Validations//
    try {
        Context db = new Context();
        ViewModel u = a;
        ModelState.Clear();
        ValidateModel(u);

        //Insert//
    }catch(Exception){...}
}