How To Validate DropDown List in Asp .net MVC - asp.net-mvc

Question

The List of the month are Already added In Databases. For Adding the salary (Create operation), i have to select the month type from the Drop Down List, if the month is not selected the program should not have to redirect to create action. How Can i validate the Drop Down, Before Routing to Create Action ?
#using(Html.BeginForm("Create","Talab",FormMethod.Post))
{
<div class="row">
<div class="form-group">
<div class="col-md-2">
Add New
</div>
</div>
<div class="form-group">
<div class="col-md-2">
#Html.DropDownListFor(model => model.Month.id, (IEnumerable<SelectListItem>)ViewData["monthType"], "--Select a Month--")
#Html.ValidationMessageFor(model => model.Month.id)
</div>
</div>
</div>
}
My View Model has following Property
public class Salary
{
public int id { get; set; }
public Nullable<int> month_id { get; set; }
[Required]
public virtual Month Month { get; set; }
public IEnumerable<Month> GetMonths()
{
IEnumerable<Month> mat = null;
mat = this.db.Months.ToList();
return mat;
}
}
Public Class Month
{
public int id { get; set; }
public string month { get; set; }
public virtual ICollection<Salary> Salary { get; set; }
}
My Controller Action Index
public ActionResult Index()
{
Salary salary = new Salary();
ViewData["monthType"] = salary .GetMonths().ToList().Select(
s => new SelectListItem
{
Text = s.month,
Value = s.id.ToString()
});
return View(salary);
}

Answer 1

Your dropdownlist should bind to property month_id which is Nullable<int>, but you have not decorated it with the [Required] attribute. It needs to be
[Required(ErrorMessage="Please select a month")]
public Nullable<int> month_id { get; set; }
and in the view
#Html.DropDownListFor(m => m.month_id, ....)
#Html.ValidationMessageFor(m => m.month_id)
Side note: You claim your using a view model, but in fact your not. What you have shown is a data model. A view model contains only properties relevant to your view and should never contain method that access your database. Refer What is ViewModel in MVC?
A view model in your case would be
public class SalaryViewModel
{
public int id { get; set; }
[Required(ErrorMessage="Please select a month")]
[Display(Name = "Month")] // for use in #Html.LabelFor()
public Nullable<int> month_id { get; set; }
public SelectList MonthList { get; set; } // or IEnumerable<SelectListItem> MonthList
}
Where you populate the MonthList property in the controller and use it in the view as
#Html.DropDownListFor(m => m.month_id, Model.MonthList, "--Select a Month--")

Answer 2

Make sure you use required on the model.
[Required]
public int id { get; set; }
Validating required selection in DropDownList
https://msdn.microsoft.com/en-us/library/system.componentmodel.dataannotations.requiredattribute(v=vs.110).aspx

Answer 3

Specify the range attribute
[Required]
[Range(1, 12, ErrorMessage="Please select a value")]
public int Id { get; set; }
Source : MVC3 validation with data-annotation?