How add custom validation to my razor page? - asp.net-mvc

Question

I have razor page in my mvc 4 application .Now imagine i have a simple textbox in my page as follows :
#Html.TextBox("Email")
or
<input id="Email" name="Email" type="text" />
how can I do some client-side validation for this field you know something like asp.net web forms validation controls . I want to make it required and write a Regex for it .

Answer 1

I use to do this:
In the model Person.cs :
[StringLength(50, ErrorMessage = "El campo {0} no puede tener mas de 50 caracteres")]
[Required(ErrorMessage = "El nombre es obligatorio")]
public string Nombre { get; set; }
In the page Create.cshtml:
<div asp-validation-summary="ModelOnly" class="text-danger"></div>
<div class="form-group">
<label asp-for="Person.Nombre" class="control-label">Nombre / Name:</label>
<input asp-for="Person.Nombre" class="form-control" />
<span asp-validation-for="Person.Nombre" class="text-danger"></span>
</div>

Answer 2

You generally decorate your model properties with the RequiredAttribute and the RegexAttribute.

Answer 3

You may want to look at Data Annotations. They provide very simple and straightforward way for you to define your (not only) validation for every field in every view model.
Please take a look at the following link:
How to: Validate Model Data Using DataAnnotations Attributes
In your particular case, it will be
[Required]
[RegularExpression(#"<your RegEx>", ErrorMessage = "<your message, leave out for default>")]
public string fieldYouValidating { get; set; }
Other way for validation preferrable by many is Fluent Validation
RuleFor(x => x.fieldYouValidating)
.NotEmpty()
.WithMessage("This is the message.");
Hope this helps