Organizing and Using Validation Attributes

Welcome to the final lesson of this course on binding and validating data in Razor Pages. In the previous lessons, we covered the basics of data binding and validation, explored advanced data binding techniques, and learned how to validate data to ensure its integrity.

In this lesson, we will focus on combining things altogether and building a full application using the techniques that we've learned. Let's dive in!

Let's apply these validation attributes to our User model. The User model will include validation for Name and Age.

User.cs

using System.ComponentModel.DataAnnotations;

public class User
{
    [Required(ErrorMessage = "Name is required.")]
    public string Name { get; set; }

    [Range(18, 100, ErrorMessage = "Age must be between 18 and 100.")]
    public int Age { get; set; }
}

In this code:

• The [Required] attribute on the Name property ensures that the name is not left empty, displaying an error message if it is.
• The [Range] attribute on the Age property ensures the age is between 18 and 100; otherwise, an error message will be shown.

As a quick reminder, the [BindProperty] attribute is used to bind form input data to model properties. In our previous lessons, we looked at how to use this attribute to link form data to model properties.

Let's see how we bind data to the UserProfileModel class using the [BindProperty] attribute:

UserProfile.cshtml.cs

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

public class UserProfileModel : PageModel
{
    [BindProperty]
    public User UserInput { get; set; }

    public void OnGet()
    {
        UserInput = new User(); // Initialize with default values
    }

    public IActionResult OnPost()
    {
        if (!ModelState.IsValid)
        {
            ViewData["Message"] = "Input data is invalid, check it and try again.";
            return Page();
        }

        // Save user profile logic

        ViewData["Message"] = "User profile saved successfully.";
        return Page(); // Stay on the same page and display a success message
    }
}

Here:

• The [BindProperty] attribute is used to bind form input data to the UserInput property.
• The OnGet() method initializes the UserInput with default values.
• The OnPost() method handles the form submission and checks if the model state is valid before proceeding with the save logic.