PageModel

Razor Pages use a C# class called PageModel to:

define data properties and associated operations for that model’s Razor page
define page handlers (like OnGet) for requests sent to that page

PageModel supports keeping all page-specifc logic and properties in their own namespace & directory.

A Page with a PageModel

Pages/Index2.cshtml

@page
@using RazorPagesIntro.Pages
@model Index2Model

<h2>Separate page model</h2>
<p>
    @Model.Message
</p>

That page’s code-behind: Pages/Index2.cshtml.cs

using Microsoft.AspNetCore.Mvc.RazorPages;
using Microsoft.Extensions.Logging;
using System;

namespace RazorPagesIntro.Pages
{
    public class Index2Model : PageModel
    {
        public string Message { get; private set; } = "PageModel in C#";

        public void OnGet()
        {
            Message += $" Server time is { DateTime.Now }";
        }
    }
}

Page Handlers

Page handlers are invoked automatically when a request is received. They separate logic from presentation.
Page handlers are defined in the PageModel class file of the associated Razor page.

Example

public Order? Order { get; set; }

public IActionResult OnGet() // Async version also exists
{
    Order = dbContext.Orders.First();
    
    return Page();
}

Example 2

using Microsoft.AspNetCore.Mvc;
using Microsoft.AspNetCore.Mvc.RazorPages;

namespace RazorPagesPizza.Pages;

public class PizzaModel : PageModel
{
    // This binds the model to the PageModel.
    [BindProperty]
    public Pizza NewPizza { get; set; }

    // An HTTP GET page handler
    public void OnGet()
    {
    }
}

Model Binding and Validation

You can bind the model to the PageModel using the BindProperty attribute:

[BindProperty]
public Pizza NewPizza { get; set; }

Both model binding and validation occur before the execution of a page handler automatically in ASP.NET Core. This means you only need to verify the outcome of the validation:

if (!ModelState.IsValid)
{
    // If ModelState is invalid, display the pizza page again to the user.
    return Page();
}

Complete Model

public class PizzaModel: PageModel
{
    
	[BindProperty]
	public Pizza NewPizza { get; set; } = new();

	public void OnGet()
	{
		pizzas = PizzaService.GetAll();
	}

	public async Task<IActionResult> OnPostAsync()
	{
		if (!ModelState.IsValid)
		{
			return Page();
		}
		
		PizzaService.Add(NewPizza);
	
		return RedirectToAction("Get");
	}
	
	public async Task<IActionResult> OnPostDelete(int id)
	{
	    PizzaService.Delete(id);
	
	    return RedirectToAction("Get");
	}
	
}