Html.HiddenFor() is used when I want to persist a field on the page but dont want the user to notice it, like the Id field and such, but does it initialize a value for the Id field? If the Id field already has a value, what does it do then? I am currently taking a course in ASP.Net MVC and I am implementing a controller that both edits and creates new customers. In order to do so, I pass a viewModel to my controller and I check if my Customer object in this viewModel has an Id that isn't equal to 0, if it is equal to 0, then this is a new customer that I need to add to my database, else I need to edit it since it actually is present in my database. So in this case, what does Html.HiddenFor() do? If I remove the Html.HiddenFor() tag from my view, when I am editing a customer, instead of being edited, it creates a new customer. Why is that? The customer I am editing already has an Id which is the key in my database, so how come his Id was treated as 0 in my controller, and so what does Html.HiddenFor() REALLY do? I have seen questions about HiddenFor before and have read the documentation but still cant get what it actually does, especially when there is indeed a field with a value other than 0(the Id field)
My Customer Class:
public class Customer
{
public int Id { get; set; }
[Required] //means that it wont be nullable
[StringLength(255)] //max len 255 instead of inf
public string Name { get; set; }
public bool IsSubscribedToNewsletter { get; set; }
[Display(Name = "Membership Type")]
public MembershipType MembershipType { get; set; } //navigation property, allows us to navigate from one type to another
[Display(Name = "Membership Type")]
public byte MembershipTypeId { get; set; } //foreign key of membership object for optimization purposes
[Display(Name = "Date of Birth")]
public DateTime? Birthdate { get; set; } //nullable
}
The Save Method in my CustomersController
[HttpPost] //make sure not httpget, if modify data, never let it be httpget
public ActionResult Save(CustomerFormViewModel viewModel) //or use updatecustomerdto (small class we create with only properties we want to update
{
if (viewModel.Customer.Id == 0)
{
_context.Customers.Add(viewModel.Customer);
}
else
{
Customer customerInDb = _context.Customers.Single(c => c.Id == viewModel.Customer.Id); //customer object in db
//need to update its properties to be like those in viemodelcustomer
//TryUpdateModel(customerInDb,"",new string[] { "Name", "Id" }); //dont use this approach since security conecerns
//name id is whitelisted as the only things to be updated
//OR
//Mapper.Map(customer, customerInDb)
customerInDb.Name = viewModel.Customer.Name;
customerInDb.Birthdate = viewModel.Customer.Birthdate;
customerInDb.MembershipTypeId = viewModel.Customer.MembershipTypeId;
customerInDb.IsSubscribedToNewsletter = viewModel.Customer.IsSubscribedToNewsletter;
}
_context.SaveChanges(); //must save changes after creating a change in the database
return RedirectToAction("Index", "Customers");
}
My CustomerFormView where the Html.HiddenFor element resides in the line before the last one
@model VidlyProject.ViewModels.CustomerFormViewModel
@{
ViewBag.Title = "New";
Layout = "~/Views/Shared/_Layout.cshtml";
}
<h2>New Customer</h2>
@using (Html.BeginForm("Save", "Customers"))
{
<!--we surround it in using since beginform creates a <form> tag not </form> so we need to close it afterwards-->
<div class="form-group">
<!--bootstrap class for a responsive form-->
@Html.LabelFor(m => m.Customer.Name) <!--label-->
@Html.TextBoxFor(m => m.Customer.Name, new { @class = "form-control" }) <!--next paramter is an anonymous object, where each element is rendered as an html attribute-->
@**\@class not class because class is reserved in c#-->**@
</div>
<div class="form-group">
@Html.LabelFor(m => m.Customer.Birthdate)
@*OR <lable for="Birthdate">Date Of Birth</label>*@
@*format string to format the date *@
@Html.TextBoxFor(m => m.Customer.Birthdate, "{0: d MMM yyyy}", new { @class = "form-control" })
</div>
<div class="form-group">
@Html.LabelFor(m => m.Customer.MembershipTypeId)
@Html.DropDownListFor(m => m.Customer.MembershipTypeId,
new SelectList(Model.MembershipTypes, @*initialize a drop down list*@
"Id", @*Name of property in membershiptype class that holds the value for each item*@
"Name"), @*Property that holds the text of each item*@
"Please select a membership type", @*message at the beginning of the dropdown*@
new { @class = "form-control"})
</div>
<div class="checkbox">
<label>
@Html.CheckBoxFor(m => m.Customer.IsSubscribedToNewsletter, new { @class = "form-check-input" }) Subscribed to the Newsletter?
</label>
</div>
@Html.HiddenFor(c => c.Customer.Id) <!--so that we set an id and the id isnt zero-->
<button type="submit" class="btn btn-primary">Save</button>
}
