Model validation

Validate Model in ActionResult

[HttpPost]
public ActionResult ContactUs(ContactUsModel contactObject)
{
    // This line checks to see if the Model is Valid by verifying each Property in the Model meets the data validation rules
    if(ModelState.IsValid)
    {
    }
    return View(contactObject);
}

The model class

public class ContactUsModel
{
    [Required]
    public string Name { get; set; }
    [Required]
    [EmailAddress] // The value must be a valid email address
    public string Email { get; set; }
    [Required]
    [StringLength(500)] // Maximum length of message is 500 characters
    public string Message { get; set; }
}

Remove an object from validation

Say you have the following model:

public class foo
{
    [Required]
    public string Email { get; set; }

    [Required]
    public string Password { get; set; }

    [Required]
    public string FullName { get; set; }
}

But you want to exclude FullName from the modelvalidation because you are using the model also in a place where FullName is not filled in, you can do so in the following way:

ModelState.Remove("FullName");

Custom Error Messages

If you want to provide Custom Error Messages you would do it like this:

public class LoginViewModel
{
    [Required(ErrorMessage = "Please specify an Email Address")]
    [EmailAddress(ErrorMessage = "Please specify a valid Email Address")]
    public string Email { get; set; }
    
    [Required(ErrorMessage = "Type in your password")]
    public string Password { get; set; }
}

When your Error Messages are in a ResourceFile (.resx) you have to specify the ResourceType and the ResourceName:

public class LoginViewModel
{
    [Required(ErrorMessageResourceType = typeof(ErrorResources), ErrorMessageResourceName = "LoginViewModel_RequiredEmail")]
    [EmailAddress(ErrorMessageResourceType = typeof(ErrorResources), ErrorMessageResourceName = "LoginViewModel_ValidEmail")]
    public string Email { get; set; }
    
    [Required(ErrorMessageResourceType = typeof(ErrorResources), ErrorMessageResourceName = "LoginViewModel_RequiredPassword")]
    public string Password { get; set; }
}

Creating Custom Error Messages in Model and in Controller

Let’s say that you have the following class:

public class PersonInfo
{
    public int ID { get; set; }

    [Display(Name = "First Name")]
    [Required(ErrorMessage = "Please enter your first name!")]
    public string FirstName{ get; set; }

    [Display(Name = "Last Name")]
    [Required(ErrorMessage = "Please enter your last name!")]
    public string LastName{ get; set; }

    [Display(Name = "Age")]
    [Required(ErrorMessage = "Please enter your Email Address!")]
    [EmailAddress(ErrorMessage = "Invalid Email Address")]
    public string EmailAddress { get; set; }
}

These custom error messages will appear if your ModelState.IsValid returns false.

But, you as well as I know that there can only be 1 email address per person, or else you will be sending emails to potentially wrong people and/or multiple people. This is where checking in the controller comes into play. So let’s assume people are creating accounts for you to save via the Create Action.

[HttpPost]
[ValidateAntiForgeryToken]
public ActionResult Create([Bind(Include = "ID, FirstName, LastName, EmailAddress")] PersonInfo newPerson)
{
    if(ModelState.IsValid) // this is where the custom error messages on your model will display if return false
    {
        if(database.People.Any(x => x.EmailAddress == newPerson.EmailAddress))  // checking if the email address that the new person is entering already exists.. if so show this error message
        {
            ModelState.AddModelError("EmailAddress", "This email address already exists! Please enter a new email address!");
            return View(newPerson);
        }
        
        db.Person.Add(newPerson);
        db.SaveChanges():
        return RedirectToAction("Index");
    }

    return View(newPerson);
}

I hope this is able to help somebody!

Model Validation in JQuery.

In cases where you need to ensure model validation using Jquery, .valid() function can be used.

The model class fields

[Required]
[Display(Name = "Number of Hospitals")]
public int Hospitals{ get; set; }
[Required]
[Display(Name = "Number of Beds")]
public int Beds { get; set; }

The View code

@using (Html.BeginForm(new {id = "form1", @class = "form-horizontal" }))
{

<div class="divPanel">
  <div class="row">
    <div class="col-md-3">                
            @Html.LabelFor(m => m.Hospitals)
            @Html.TextBoxFor(m => m.Hospitals, new { @class = "form-control", @type = "number"})
            @Html.ValidationMessageFor(m => m.Hospitals)

    </div>
    <div class="col-md-3">

            @Html.LabelFor(m => m.Beds)
            @Html.TextBoxFor(m => m.Beds, new { @class = "form-control", @type = "number"})
            @Html.ValidationMessageFor(m => m.Beds)
    </div>
<div class="col-md-3">             
        <button type=button  class="btn btn-primary" id="btnCalculateBeds"> Calculate Score</button>
    </div>
 </div>

  </div>
 }

The script for Validation check.

$('#btnCalculateBeds').on('click', function (evt) {
evt.preventDefault();

if ($('#form1').valid()) {
//Do Something.
}
}

Ensure that the jquery.validate and jquery.validate.unobtrusive files are present in the solution.