The value '' is not valid for

Question

I have a Blazor web application which uses System.ComponentModel.DataAnnotations attribute for validation in a registration form.
I have a property named NationalCode which is nullable long
I did not added [Required] attribute above my NationalCode property
But when I want to submit the form if I leave the field NationalCode empty this validation message appears
"The value '' is not valid for 'NationalCode'."

If I change my code and add [Required] attribute like this :

[Required(ErrorMessage = "Please Enter your national code", AllowEmptyStrings = true)]
public long? NationalCode { get; set; } = null;

Two message appears :

- "The value '' is not valid for 'NationalCode'."
- "Please Enter your national code"

But I want only my message appear.
Where is the first message come from ?
How can I disable it ?

This is my codes :

<div class="form-floating">
    <InputNumber @bind-Value="Input.NationalCode" autocomplete="nationalCode" aria-required="true" />
    <label for="family">NationalCode</label>
    <ValidationMessage For="() => Input.NationalCode" class="text-danger" />
</div>

 private sealed class InputModel
 {
     public long? NationalCode { get; set; }
 }

.NET Version

8.0.3

Answer 1

First you need to clear the statement. Let's look at "Required(ErrorMessage = "Please Enter your national code", AllowEmptyStrings = true)]". So, is NationalCode required or it can be empty?

After that, you will be able to program it.

P. S. You can declare the property as

public string NationalCode { get; set; } = string.Empty;

It provides with an empty string as the initial value to display. It can be easier than other solutions like to obtain a valid code.

Answer 2

I've taken the code you've provided and produced this Minimal Reproducible Example.

It works, so there must be doing something you're not showing.

@page "/"
@using System.ComponentModel.DataAnnotations

<PageTitle>Home</PageTitle>

<h1>Hello, world!</h1>

Welcome to your new app.

<EditForm EditContext="_editContext" OnValidSubmit="this.OnValidSubmit">
    <DataAnnotationsValidator/>
    <div class="mb-3">
        <label class="form-label">National Code</label>
        <InputNumber class="form-control" @bind-Value="_model.NationalCode" autocomplete="nationalCode" aria-required="true" />
        <ValidationMessage For="() => _model.NationalCode" class="text-danger" />
    </div>
    <div class="text-end">
        <button tyoe="submit" class="btn btn-primary">Submit</button>
    </div>
</EditForm>

<div class="bg-dark text-white m-2 p-2">
    <pre>Value: @(_model.NationalCode?.ToString() ?? "null")</pre>
</div>
@code{
    private Model _model = new();
    private EditContext? _editContext;

    protected override void OnInitialized()
    {
        _editContext = new(_model);
    }

    public Task OnValidSubmit()
    {
        return Task.CompletedTask;    
    }

    public class Model {
        public long? NationalCode { get; set; } = null;
    }
}