How to customize the default error message "The value '' is invalid"

Divine Fokwa

I am new to asp.net core. I have a form which is generated dynamically. I want the validation error message to be "The value must be numeric" instead I get

"The value 'a' is invalid."

Here is my View Model:

[RegularExpression("^[0-9]*$", ErrorMessage = "The value must be numeric")]
public List Units_Service { get; set; }

Here is my form code:

for (int i = 0; i < Model.Workload_Category_Name.Count; i++)
{
   
       
             @Html.DisplayFor(model => model.Workload_Category_Name[i]) 
       
       
          @Html.TextBoxFor(model => model.Units_Service[i], new { style = "width: 15%", MaskedTextBox = "9999" })
          @Html.ValidationMessageFor(model => model.Units_Service[i])
       
   
 }

Despite the fact, I have put the custom error message in my View Model as shown above, I keep getting the default message "The value '' is invalid". Please what is the solution to this kind of scenario ?

1 Reply

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Mahesh Chand2y ago

You need to customize the error message somewhere. Something like this I got from ChatGPT :)

In the Model:
You can use data annotations to customize the error messages on properties.

public class YourModel
{
    [Required(ErrorMessage = "Please enter a value")]
    public string YourProperty { get; set; }
}

In the Controller:
You can customize the error response based on the model state.

[HttpPost]
public ActionResult YourAction(YourModel model)
{
    if (!ModelState.IsValid)
    {
        // Adding a custom error message
        ModelState.AddModelError("", "Custom error message here");
        
        return View(model);
    }
    
    // Your code here if the model is valid
    
    return RedirectToAction("SuccessAction");
}

In the View:
Display the error message using the validation summary or display it next to the field.

@using (Html.BeginForm()) 
{
    @Html.ValidationSummary(true, "", new { @class = "text-danger" })
    
    
}