In this article I will explain with an example, how to perform validation inside Controller i.e. Server Side validation in ASP.Net MVC Razor.
Validations in ASP.Net MVC Razor can be performed on Client Side as well as Server Side using Data Annotation attributes.
Note: If you want to learn about Client Side validations in ASP.Net MVC, please refer ASP.Net MVC: Client Side validations using Data Annotation attributes and jQuery.
 
 
Model
The following Model class consists of one property Name. The property is decorated with the following Data Annotation attributes for performing validations.
1. Required Data Annotation attribute.
The Data Annotations attributes can be used with the Entity Data Model (EDM), LINQ to SQL, and other data models.
The Required Data Annotation has been specified with a property Error Message with a string value. As the name suggests, this string value will be displayed to the user when the validation fails.
using System.ComponentModel.DataAnnotations;
 
namespace TextBox_Validation_MVC.Models
{
    public class PersonModel
    {
        [Required(ErrorMessage = "Name is required.")]
        public string Name { get; set; }
    }
}
 
 
Controller
The Controller consists of following two Action methods.
Action method for handling GET operation
Inside this Action method, simply the View is returned.
 
Action method for handling POST operation
This Action method handles the POST operation and when the form is submitted, the object of the PersonModel class is sent to this method.
The state of the submitted Model is checked using ModelState.IsValid property and if the Model is valid then the value of the Name property is set in a ViewBag object.
Note: ModelState.IsValid property is an inbuilt property which verifies two things:
1. Whether the Form values are bound to the Model.
2. All the validations specified inside Model class using Data annotations have been passed.
 
public class HomeController : Controller
{
    // GET: Home
    public ActionResult Index()
    {
        return View();
    }
 
    [HttpPost]
    public ActionResult Index(PersonModel person)
    {
        if (ModelState.IsValid)
        {
            ViewBag.Name = person.Name;
        }
 
        return View();
    }
}
 
 
View
Inside the View, in the very first line the PersonModel class is declared as Model for the View.
The View consists of an HTML Form which has been created using the Html.BeginForm method with the following parameters.
ActionName – Name of the Action. In this case the name is Index.
ControllerName – Name of the Controller. In this case the name is Home.
FormMethod – It specifies the Form Method i.e. GET or POST. In this case it will be set to POST.
 
The Form consists of the following there HTML Helper functions:-
1. Html.LabelFor – Displaying the Model property name.
2. Html.TextBoxFor – Creating a TextBox for the Model property.
3. Html.ValidationMessageFor – Displaying the Validation message for the property.
There is also Submit button which when clicked, the Form gets submitted.
 
Displaying submitted value
Below the Form, the ModelState.IsValid property is checked and if the Model is valid, then the value if the ViewBag object is displayed using Razor syntax in ASP.Net MVC.
@model TextBox_Validation_MVC.Models.PersonModel
@{
    Layout = null;
}
 
<!DOCTYPE html>
 
<html>
<head>
    <meta name="viewport" content="width=device-width" />
    <title>Index</title>
    <style type="text/css">
        body { font-family: Arial; font-size: 10pt; }
        .error { color: red; }
    </style>
</head>
<body>
    @using(Html.BeginForm("Index", "Home", FormMethod.Post))
    {
        <table>
            <tr>
                <td>@Html.LabelFor(m => m.Name)</td>
                <td>@Html.TextBoxFor(m => m.Name)</td>
                <td>@Html.ValidationMessageFor(m => m.Name, "", new { @class = "error" })</td>
            </tr>
            <tr>
                <td></td>
                <td><input type="submit" value="Submit" /></td>
                <td></td>
            </tr>
        </table>
    }
    <hr/>
    @if (ViewData.ModelState.IsValid)
    {
        @ViewBag.Name;
    }
</body>
</html>
 
 
Screenshot
Validation inside Controller (Server Side validation) in ASP.Net MVC
 
 
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