ASP MVC Validation - asp.net-mvc

Question

I need to perform validation on a textbox and Dropdown which triggers only when both the values are empty and does nothing when one of the value is empty. How would i implement it? Do i need to create a custom validator? Below is my Model and View
Model
public class CustomValidators
{
[Required]
[Required(ErrorMessage = "State Required")]
public string drpStateId { set; get; }
public System.Web.Mvc.SelectList drpState { set; get; }
[Required(ErrorMessage ="Region Required")]
public string txtRegion { set; get; }
}
View
#model InterviewTest.Models.CustomValidators
#{
ViewBag.Title = "Custom Validator";
Layout = "~/Views/_Layout.cshtml";
}
<p>#Html.ActionLink("< Back", "Index")</p>
#using (Html.BeginForm("CustomValidatorPost"))
{
#Html.ValidationSummary()
<div class="container-fluid">
<div class="row">
<div class="col-sm-3">
<div class="form-group">
#Html.DropDownListFor(c => c.drpStateId, Model.drpState, "", new { #class = "form-control" })
</div>
</div>
<div class="col-sm-6">
<div class="form-group">
#Html.TextBoxFor(x => Model.txtRegion, new { #class = "form-control" })
#*<input type="text" id="txtRegion" name="txtRegion" class="form-control" />*#
</div>
</div>
<div class="col-sm-3">
<button type="submit" name="btnSubmit" id="btnSubmit" class="btn btn-default">Submit</button>
</div>
</div>
</div>
}

Answer 1

There is no out of the box validation that works on 2 fields except for the compare validator, so in your case you have to create a custom validation.
You can create a JavaScript function and fire it on onchange on both the two text boxes and within it check the values and if both are empty, show an error message and prevent the form from being submitted, you can achieve that using JQuery validation by adding a custom validator, see this link for more details https://jqueryvalidation.org/jQuery.validator.addMethod/
On Server side, you can do a simple if statement in the controller action to validate that both the values are not empty and if both are empty, then add an error to the ModelState