Laravel Validation and Error Handling

# CHAPTER 12

Laravel Validation and Error Handling #

1. Introduction #

2. Learning Objectives #

• Use the $request->validate() method in a Controller.

• Apply multiple validation rules (required, unique, min/max length).

• Display validation error messages in Blade views.

• Understand how Laravel handles automatic redirection upon failure.

3. Beginner-Friendly Explanation #

4. Basic Validation in the Controller #

app/Http/Controllers/PostController.php

public function store(Request $request)
{
    // 1. The Bouncer checks the rules
    $validatedData = $request->validate([
        'title' => 'required|max:255', // Must not be empty, max 255 chars
        'content' => 'required|min:10', // Must be at least 10 chars
        'author_email' => 'required|email|unique:users,email' // Must be a valid email, and unique in the users table
    ]);

    // 2. If the data FAILS, Laravel automatically stops executing here.
    // It instantly redirects the user back to the form with errors attached to the session.

    // 3. If the data PASSES, execution continues and we save to the database!
    Post::create($validatedData);

    return redirect('/posts')->with('success', 'Post created safely!');
}

5. Displaying Errors in Blade #

resources/views/posts/create.blade.php

<form method="POST" action="/posts">
    @csrf

    <label>Title</label>
    <!-- We use the old() helper so the user doesn&#039;t lose what they typed! -->
    <input type="text" name="title" value="{{ old(&#039;title') }}">
    
    <!-- Display the specific error for &#039;title' -->
    @error(&#039;title')
        <div style="color: red;">{{ $message }}</div>
    @enderror

    <label>Content</label>
    <textarea name="content">{{ old(&#039;content') }}</textarea>
    
    @error(&#039;content')
        <div style="color: red;">{{ $message }}</div>
    @enderror

    <button type="submit">Save</button>
</form>

6. Displaying a Summary of All Errors #

@if ($errors->any())
    <div class="alert alert-danger">
        <ul>
            @foreach ($errors->all() as $error)
                <li>{{ $error }}</li>
            @endforeach
        </ul>
    </div>
@endif

7. Customizing Error Messages #

$request->validate(
    ['title' => 'required'],
    ['title.required' => 'Hey! You forgot to type a headline!']
);

8. Exception Handling #

9. Best Practices #

• Never Trust Frontend Validation: Adding required to your HTML <input> tags is great for user experience, but it is not security. Hackers bypass HTML and send POST requests directly via Postman. You MUST validate on the backend in Laravel.

10. Common Mistakes #

• Losing User Data on Redirect: If a user types a 500-word blog post, but forgets to enter the Title, Laravel redirects them back. If you do not use the old('content') helper in your <textarea>, the 500 words will be erased, and the user will be furious. Always use old('field_name') to repopulate forms.

11. Exercises #

1. 1. Trace the execution flow: A user submits a form without an email address. The Controller dictates that the email is required. What exactly does Laravel do next?

12. Coding Challenges #

• Challenge: Write the validation rules for a Registration form. The username must be required, alphanumeric, and unique in the users table. The password must be required and at least 8 characters long.

13. MCQs with Answers #

14. Interview Questions #

• Q: Explain how Laravel's $request->validate() method protects a database from bad data.

• Q: If an attacker bypasses client-side HTML validation, how does Laravel's backend validation ensure the application remains secure, and how is the unique:table,column rule critical for user registration?

15. FAQs #

16. Summary #

17. Next Chapter Recommendation #