MVC model validation - asp.net-mvc

Question

So, im currently building an application that needs the user model validating, and if the incorrect properties are filled in to the user it will tell them.
I have the data annotations set up, but im not sure how i relay the error message back to the user?
I have this set up so far on my model and view.
Model
public class DatabaseModel
{
[Required(ErrorMessage = ("A first name is required"))]
public string FirstName { get; set; }
[Required(ErrorMessage = ("A last name is required"))]
public string LastName { get; set; }
[Required(ErrorMessage = ("A valid role is required"))]
public string Role { get; set; }
// TODO - Validate rank to only b 1 - 10
//
[Range(1,10, ErrorMessage = ("A rank between 1 and 10 is required"))]
public int Rank { get; set; }
}
And View
#model RoleCreatorAndEditor.Models.DatabaseModel
#{
ViewData["Title"] = "Index";
}
<h2>User Information</h2>
<p>This is your user information!</p>
#using (Html.BeginForm("Index", "Home", FormMethod.Post)) {
#Html.Label("First Name")
<br>
#Html.TextBoxFor(m => m.FirstName)
<br>
#Html.Label("Last Name")
<br>
#Html.TextBoxFor(m=>m.LastName)
<br>
#Html.Label("Role")
<br>
#Html.TextBoxFor(m => m.Role)
<br>
#Html.Label("Rank")
<br>
#Html.TextBoxFor(m => m.Rank)
<br><br>
<input type="submit" value="Save">
}
My Controller
public class HomeController : Controller
{
// GET: Home
[HttpGet]
public ActionResult Index()
{
DatabaseModel model = new DatabaseModel();
return View(model);
}
[HttpPost]
public ActionResult Index(DatabaseModel model)
{
if (ModelState.IsValid)
{
ListToDatatable convert = new ListToDatatable();
DataTable user = convert.Convert(model);
DatabaseRepository dbRepo = new DatabaseRepository();
dbRepo.Upload(user);
}
return View();
}
}
I believe the model needs to be passed back to the view in order to display the error message, and although i have read through the documentation on asp.net i cannot understand how they just add the error message and the form knows how to display the errors to the user.
I am extremely confused.

Answer 1

You need to use ModelState.IsValid in your Controller and also #Html.ValidationMessageFor(model => model.FirstName) in your view:
public ActionResult Index(ViewModel _Model)
{
// Checking whether the Form posted is valid one.
if(ModelState.IsValid)
{
// your model is valid here.
// perform any actions you need to, like database actions,
// and/or redirecting to other controllers and actions.
}
else
{
// redirect to same action
return View(_Model);
}
}
For your example:
#model RoleCreatorAndEditor.Models.DatabaseModel
#{
ViewData["Title"] = "Index";
}
<h2>User Information</h2>
<p>This is your user information!</p>
#using (Html.BeginForm("Index", "Home", FormMethod.Post)) {
#Html.LabelFor(m=>m.FirstName)
<br>
#Html.TextBoxFor(m => m.FirstName)
#Html.ValidationMessageFor(model => model.FirstName, "", new { #class = "text-danger" })
<br>
#Html.LabelFor(m=>m.LastName)
<br>
#Html.TextBoxFor(m=>m.LastName)
#Html.ValidationMessageFor(model => model.LastName, "", new { #class = "text-danger" })
. . .
<input type="submit" value="Save">
}
Controller:
[HttpPost]
public ActionResult Index(DatabaseModel model)
{
if (ModelState.IsValid)
{
ListToDatatable convert = new ListToDatatable();
DataTable user = convert.Convert(model);
DatabaseRepository dbRepo = new DatabaseRepository();
dbRepo.Upload(user);
}
return View(model);
}