Question

For a simple validation of multiple required fields i am using a custom validator explained here

I am getting the desired behavior and validation summary message is displayed correctly, but what i am missing now is the lack of validation error css class on invalid input elements,
which is added when built-in validators are used.

This is the correct behavior:

<input class="input-validation-error" name="ModelName" ... />

And this is what i get when using mentioned custom validator:

<input name="ModelName" ... />

Please note that i am referring to server side validation.

UPDATE

This is my model:

public class Register
{
        [MultiFieldRequired(new[] { "Name", "UserName" }, ErrorMessage = "Please provide all required information")]
        [Display(Name = "Name")]
        public string Name { get; set; }

        [MultiFieldRequired(new[] { "Name", "UserName" }, ErrorMessage = "Please provide all required information")]
        [Display(Name = "User name")]
        public string UserName { get; set; }
}

And this is the rendered output:

<input class="text-box single-line" data-val="true" data-val-multifield="Please provide all required information" id="Name" name="Name" type="text" value="" />
<input class="text-box single-line" data-val="true" data-val-multifield="Please provide all required information" id="UserName" name="UserName" type="text" value="" />

I am now realizing that the problem i had only occurs when i decorate my entire model class with the MultiFieldRequired attribute:

[MultiFieldRequired(new[] { "Name", "UserName" }, ErrorMessage = "Please provide all required information")]
public class Register
{
...

In this case no invalid field has modified css class, while in the other scenario, when i annotate every field in the model i get the same error message multiplied by the number of invalid fields.

So, to summarize – i want to have one error message regardless of the
number of invalid fields and I also want that each invalid field be
marked with .input-validation-error class.

Answer 1

I was expecting that invalid fields in the view will be marked with .input-validation-error class regardles of the position of the attribute, so i used the custom validator attribute to annotate my model class like this:

[MultiFieldRequired(new[] { "Name", "UserName" }, ErrorMessage = "Please provide all required information")]
public class Register
{
        [Display(Name = "Name")]
        public string Name { get; set; }

        [Display(Name = "User name")]
        public string UserName { get; set; }
}

On the other hand, if i annotate each field:

public class Register
{
        [MultiFieldRequired(new[] { "Name", "UserName" }, ErrorMessage = "Please provide all required information")]
        [Display(Name = "Name")]
        public string Name { get; set; }

        [MultiFieldRequired(new[] { "Name", "UserName" }, ErrorMessage = "Please provide all required information")]
        [Display(Name = "User name")]
        public string UserName { get; set; }
}

my view generates multiple identical messages in the validation summary.

So i ended up having a a custom validation summary error message using ValidationSummary like this:

@Html.ValidationSummary(true, "Please provide all required information")

and my fields are decorated with simple asterisks like this:

public class Register
{
        [Required(ErrorMessage = "*")]
        [Display(Name = "Name")]
        public string Name { get; set; }

        [Required(ErrorMessage = "*")]
        [Display(Name = "User name")]
        public string UserName { get; set; }
}

At the end, my view is rendered like this:

HTH