MVC model validation

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.

Include `@Html.ValidationMessageFor(m => m.FirstName)` etc in the view (and include the relevant scripts for client side validation. In the controller you also need `if(!ModelState.IsValid) { return View(model); }` — , Oct 27 '16 at 08:44
Possible duplication of this ticket. http://stackoverflow.com/questions/5739362/modelstate-addmodelerror-how-can-i-add-an-error-that-isnt-for-a-property — karman, Oct 27 '16 at 08:50
@karman i don't understand the answer to that ticket nor do i understand how to use that on my own problem — Ryan white, Oct 27 '16 at 08:51
Errors are added by this way. ModelState.AddError method http://stackoverflow.com/questions/5739362/modelstate-addmodelerror-how-can-i-add-an-error-that-isnt-for-a-property — karman, Oct 27 '16 at 08:53
That still isn't help me understand it, but as @StephenMuecke has explained it to me i understand it better. — Ryan white, Oct 27 '16 at 08:54

score 1 · Accepted Answer · edited Sep 23 '17 at 05:33

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);
}

Sorry i forgot the code to my controller, ill update my question now. — Ryan white, Oct 27 '16 at 08:45
so i have my model passed into my ccontrolr, and i have the IsValid, but its after this point i get confused — Ryan white, Oct 27 '16 at 08:47
Not much good without including the relevant `@Html.ValidationMessageFor()` for each property in the view :) — , Oct 27 '16 at 08:47
@StephenMuecke so the @html.validationMessageFor(), how exactly do i use this? i do apologize for all the nooby questions, i have never handled MVC before. — Ryan white, Oct 27 '16 at 08:49
@Ryanwhite - See my comment to your question - you just need one for each property (and use `@Html.LabelFor(m => m.FirstName)` not `Label()`) And use `return View(model);` - always pass a model — , Oct 27 '16 at 08:51

MVC model validation

1 Answers1

For your example:

Controller:

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