Exercise - Add new pizza form

10 minutes

In this unit, you'll finish the Pizza List page by adding a form to create new pizzas. You'll also add page handlers to handle the form submission and deletion of pizzas.

Add a form to create new pizzas

Let's start by adding properties to the PizzaListModel class to represent the user's input. You'll add the appropriate page handler, too.

Open Pages\PizzaList.cshtml.cs and add the following property to the PizzaListModel class:
```
[BindProperty]
public Pizza NewPizza { get; set; } = default!;
```
In the preceding code:
- A property named NewPizza is added to the PizzaListModel class.
  - NewPizza is a Pizza object.
- The BindProperty attribute is applied to the NewPizza property.
  - The BindProperty attribute is used to bind the NewPizza property to the Razor page. When an HTTP POST request is made, the NewPizza property will be populated with the user's input.
- The NewPizza property is initialized to default!.
  - The default! keyword is used to initialize the NewPizza property to null. This prevents the compiler from generating a warning about the NewPizza property being uninitialized.
Now add the page handler for HTTP POST. In the same file, add the following method to the PizzaListModel class:
```
public IActionResult OnPost()
{
    if (!ModelState.IsValid || NewPizza == null)
    {
        return Page();
    }

    _service.AddPizza(NewPizza);

    return RedirectToAction("Get");
}
```
In the preceding code:
- The ModelState.IsValid property is used to determine if the user's input is valid.
  - The validation rules are inferred from attributes (such as Required and Range) on the Pizza class in Models\Pizza.cs.
  - If the user's input is invalid, the Page method is called to re-render the page.
- The NewPizza property is used to add a new pizza to the _service object.
- The RedirectToAction method is used to redirect the user to the Get page handler, which will re-render the page with the updated list of pizzas.
Save the file. If you're using GitHub Codespaces, the file saves automatically.
Return to the terminal running dotnet watch and press Ctrl+R to reload the app.

Now that there's a page handler to handle the form submission, let's add the form to the Razor Page.

Open Pages\PizzaList.cshtml and replace the  with the following code:

<form method="post">
<div asp-validation-summary="ModelOnly" class="text-danger"></div>
<div class="form-group">
    <label asp-for="NewPizza.Name" class="control-label"></label>
    <input asp-for="NewPizza.Name" class="form-control" />
    <span asp-validation-for="NewPizza.Name" class="text-danger"></span>
</div>
<div class="form-group">
    <label asp-for="NewPizza.Size" class="control-label"></label>
    <select asp-for="NewPizza.Size" class="form-control" id="PizzaSize">
        <option value="">-- Select Size --</option>
        <option value="Small">Small</option>
        <option value="Medium">Medium</option>
        <option value="Large">Large</option>
    </select>
    <span asp-validation-for="NewPizza.Size" class="text-danger"></span>
</div>
<div class="form-group form-check">
    <label class="form-check-label">
        <input class="form-check-input" asp-for="NewPizza.IsGlutenFree" /> @Html.DisplayNameFor(model => model.NewPizza.IsGlutenFree)
    </label>
</div>
<div class="form-group">
    <label asp-for="NewPizza.Price" class="control-label"></label>
    <input asp-for="NewPizza.Price" class="form-control" />
    <span asp-validation-for="NewPizza.Price" class="text-danger"></span>
</div>
<div class="form-group">
    <input type="submit" value="Create" class="btn btn-primary" />
</div>
</form>

In the preceding code:

The asp-validation-summary attribute is used to display validation errors for the entire model.
Each form field (<input> and <select> elements) and each <label> is bound to the corresponding NewPizza property using the asp-for attribute.
The asp-validation-for attribute is used to display any validation errors for each form field.
The @Html.DisplayNameFor method is used to display the display name for the IsGlutenFree property. This is a Razor helper method that's used to display the display name for a property. Doing the label this way ensures that the checkbox is selected when the user clicks the label.
A submit button labeled Create is added to the form to post the form data to the server. At runtime, when the user selects this Create button, the browser sends the form as an HTTP POST request to the server.

At the bottom of the page, add the following code:
```
@section Scripts {
<partial name="_ValidationScriptsPartial" />
}
```
This injects the client-side validation scripts into the page. The client-side validation scripts are used to validate the user's input before the form is submitted to the server.
Save the file. In the browser, the Pizza List page refreshes with the new form. If you're using GitHub Codespaces, the file saves automatically, but you'll need to refresh the browser tab manually.
Enter a new pizza and select the Create button. The page should refresh and display the new pizza in the list.

Add a page handler to delete pizzas

There's one last piece to add to the Pizza List page: a page handler to delete pizzas. The buttons to delete pizzas are already on the page, but they don't do anything yet.

Back in Pages\PizzaList.cshtml.cs, add the following method to the PizzaListModel class:
```
public IActionResult OnPostDelete(int id)
{
    _service.DeletePizza(id);

    return RedirectToAction("Get");
}
```
In the preceding code:
- The OnPostDelete method is called when the user clicks the Delete button for a pizza.
  - The page knows to use this method because the asp-page-handler attribute on the Delete button in Pages\PizzaList.cshtml is set to Delete.
- The id parameter is used to identify the pizza to delete.
  - The id parameter is bound to the id route value in the URL. This is accomplished with the asp-route-id attribute on the Delete button in Pages\PizzaList.cshtml.
- The DeletePizza method is called on the _service object to delete the pizza.
- The RedirectToAction method is used to redirect the user to the Get page handler, which will re-render the page with the updated list of pizzas.
Save the file. If you're using GitHub Codespaces, the file saves automatically.
Test the Delete button for a pizza. The page should refresh and the selected pizza should be removed from the list.

Congratulations! You've successfully created a Razor Page that displays a list of pizzas, allows the user to add new pizzas, and also allows the user to delete pizzas.

Exercise - Add new pizza form

Add a form to create new pizzas

Add a page handler to delete pizzas

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