I am using ASP.NET Core MVC with C#.
I define my model like this:
public class Student
{
public class FirstName {get;set;}
public int? PriorityId { get; set; }
}
public class Priority
{
[Key]
public int PriorityId { get; set; }
[Required]
[Display(Name = "Priority Name")]
public string Name { get; set; }
}
So it will render HTML for priority dropdown like this.
<div class="col-sm-4">
<div class="form-group">
<label for="Student_PriorityId">Priority<span style="color:red"> *</span></label>
<select class="form-control valid" id="Student_PriorityId" name="Student.PriorityId" aria-invalid="false">
<option selected="selected" value="0">Select</option>
<option value="3">High</option>
<option value="1">Low</option>
<option value="2">Medium</option>
</select>
<span class="text-danger field-validation-error" data-valmsg-for="Student.PriorityId" data-valmsg-replace="true">Priority is required.</span>
</div>
</div>
Problem
When I am going to check custom validation the message is not display below dropdown.
if (obj.Student.PriorityId <= 0)
{
ModelState.AddModelError(nameof(obj.Student.PriorityId), "Priority is required.");
}
The above code is not working when I try using nameof()
.
But when I remove nameof()
and write down as string like below. It shows me error message below drop down successfully.
if (obj.Student.PriorityId <= 0)
{
ModelState.AddModelError("Student.PriorityId", "Priority is required.");
}
Is there any way where I can improve nameof()
function of C#?
I'm not sure this is an improvement but you could write a method like this:
public static string NameOf<T>(Expression<Func<T>> func)
{
return string.Join(".", func.ToString().Split('.').Reverse().Take(3).Reverse().ToArray());
}
Then your code would be
if (obj.Student.PriorityId <= 0)
{
ModelState.AddModelError(NameOf( () => obj.Student.PriorityId ), "Priority is required.");
}
In this case, NameOf
would return "obj.Student.PriorityId".
Here is an example of how to use CallerArgumentExpressionAttribute
as a replacement for nameof
.
using Microsoft.AspNetCore.Mvc.ModelBinding;
using System.Runtime.CompilerServices;
public static class ModelStateExtensions
{
public static void AddModelErrorEx(
this ModelStateDictionary modelStateDictionary,
object _,
string errorMessage,
[CallerArgumentExpression("_")] string expr = "")
=> modelStateDictionary.AddModelError(expr, errorMessage);
}
Usage:
// Argument 'expr' will be "Student.PriorityId" here.
ModelState.AddModelErrorEx(Student.PriorityId, "Priority is required.")
// Argument 'expr' will be "obj.Student.PriorityId" here.
ModelState.AddModelErrorEx(obj.Student.PriorityId, "Priority is required.")
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