Forms, Model Binding and Validation in ASP.NET Core

Introduction

Model binding is the magic that turns HTTP form fields into C# objects. Combined with validation and anti-forgery tokens, it powers ShopNest user registration and login safely.

After this article you will

• Build forms with Tag Helpers and model binding
• Use [FromForm], [FromQuery], [FromRoute], [FromBody]
• Enable client-side jQuery unobtrusive validation
• Protect forms with anti-forgery tokens

Prerequisites

• Article 9 — Models and ViewModels
• ShopNest.Web project from prior lessons

Concept deep-dive

When a form posts, the model binder walks the request: form fields → properties by name match. Nested objects use dot notation: Address.City. Collections use indexed names: Phones[0].Number.

<form asp-action="Register" method="post">
  @Html.AntiForgeryToken()
  <input asp-for="Email" />
  <span asp-validation-for="Email"></span>
  <div asp-validation-summary="ModelOnly"></div>
</form>

Enable client validation in _Layout: jquery.validate + jquery.validate.unobtrusive. Custom rules: inherit ValidationAttribute.

Hands-on — ShopNest User Registration Form

1. RegisterViewModel with password confirm custom validation.
2. GET shows form; POST validates and creates user (stub).
3. Display validation summary and field errors.
4. Verify __RequestVerificationToken in request (DevTools).

Common errors & best practices

• Binding fails silently — check property names match input name attributes.
• CSRF: always [ValidateAntiForgeryToken] on POST mutating actions.
• Complex types need [FromForm] when mixing sources.

Interview questions

Q: How does model binding work?
A: Value providers read route/query/form/body; binder sets action parameters and ModelState.

Q: What is anti-forgery?
A: Synchronizer token pattern — hidden field + cookie validated on POST.

Summary

• Model binding maps HTTP data to C# automatically
• Validate with Data Annotations + ModelState
• Anti-forgery prevents CSRF on registration forms

Previous: Models and ViewModels
Next: Tag Helpers

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