Model events and observers in Laravel

Introduction

Model events let you run code automatically when something happens to your data. Observers help organize this code neatly.

You want to send a welcome email when a new user signs up.

You need to log changes whenever a product is updated.

You want to clean up related data when a record is deleted.

You want to automatically set a value before saving a model.

You want to keep your code organized by separating event logic.

Syntax

Laravel

php
// Creating an observer class
class UserObserver {
    public function created(User $user) {
        // code to run after a user is created
    }

    public function updated(User $user) {
        // code to run after a user is updated
    }
}

// Registering the observer in a service provider
User::observe(UserObserver::class);

Observer methods match model events like created, updated, deleted.

Register observers usually in AppServiceProvider or a dedicated provider.

Examples

This observer deletes all comments before a post is deleted.

Laravel

php
class PostObserver {
    public function deleting(Post $post) {
        // Remove related comments before deleting a post
        $post->comments()->delete();
    }
}

Post::observe(PostObserver::class);

This observer sends a notification after a new order is created.

Laravel

php
class OrderObserver {
    public function created(Order $order) {
        // Send notification when order is created
        Notification::send($order->user, new OrderPlaced($order));
    }
}

Order::observe(OrderObserver::class);

Sample Program

This example shows a User model and a UserObserver that logs a message when a user is created. The observer is registered in the AppServiceProvider.

Laravel

<?php

namespace App\Models;

use Illuminate\Database\Eloquent\Model;

class User extends Model
{
    // User model code
}

namespace App\Observers;

use App\Models\User;
use Illuminate\Support\Facades\Log;

class UserObserver
{
    public function created(User $user)
    {
        Log::info("User created: {$user->email}");
    }
}

namespace App\Providers;

use Illuminate\Support\ServiceProvider;
use App\Models\User;
use App\Observers\UserObserver;

class AppServiceProvider extends ServiceProvider
{
    public function boot()
    {
        User::observe(UserObserver::class);
    }
}

// When a new user is created, a log entry is made automatically.

Important Notes

Model events include: creating, created, updating, updated, deleting, deleted, saving, saved, restoring, restored.

Observers keep your code clean by separating event logic from models.

Remember to register observers to activate them.

Summary

Model events let you run code when data changes.

Observers organize event code in separate classes.

Register observers to connect them with models.

Practice

1. What is the main purpose of model events in Laravel?

easy

A. To react automatically when a model is created, updated, or deleted

B. To define database table relationships

C. To create database migrations

D. To write raw SQL queries

Solution

1. Step 1: Understand model events

   Model events are hooks that trigger when a model changes, like creation or deletion.

2. Step 2: Identify their purpose

   They let you run code automatically on these changes, such as logging or notifications.

3. Final Answer:

   To react automatically when a model is created, updated, or deleted -> Option A

4. Quick Check:

   Model events = react on model changes [OK]

Hint: Model events trigger on data changes automatically [OK]

Common Mistakes:

• Confusing events with database migrations
• Thinking events define relationships
• Assuming events run SQL queries directly

2. Which of the following is the correct way to register an observer for a model in Laravel?

easy

A. User::addObserver('UserObserver');

B. User::observe(UserObserver::class);

C. User::registerObserver(UserObserver);

D. User::attachObserver(UserObserver::class);

Solution

1. Step 1: Recall observer registration syntax

   Laravel uses the static method observe() on the model to register observers.

2. Step 2: Match correct syntax

   The correct syntax is Model::observe(ObserverClass::class); which matches User::observe(UserObserver::class);.

3. Final Answer:

   User::observe(UserObserver::class); -> Option B

4. Quick Check:

   Register observer = observe() method [OK]

Hint: Use observe() method with ::class for observers [OK]

Common Mistakes:

• Using wrong method names like registerObserver
• Passing observer as string instead of ::class
• Confusing attachObserver with observe

3. Given this observer method in Laravel:

public function created(User $user) {
    Log::info('User created: ' . $user->id);
}

What happens when a new User model is saved?

medium

A. An error is thrown because created() is invalid

B. The user is deleted immediately

C. Nothing happens automatically

D. A log entry with the new user's ID is created

Solution

1. Step 1: Understand the created() observer method

   The created() method runs after a model is saved for the first time.

2. Step 2: Analyze the method body

   It logs info with the new user's ID, so a log entry is made.

3. Final Answer:

   A log entry with the new user's ID is created -> Option D

4. Quick Check:

   created() logs user ID after save [OK]

Hint: created() runs after first save, logs info [OK]

Common Mistakes:

• Thinking created() deletes the model
• Assuming created() does nothing
• Confusing created() with invalid method

4. What is wrong with this observer registration code?

public function boot() {
    User::observe();
}

medium

A. The observe() method is called without passing the observer class

B. The boot() method should be named bootObserver()

C. User model cannot have observers

D. The observe() method should be called on the observer class

Solution

1. Step 1: Check observe() method usage

   observe() requires the observer class as an argument to register it.

2. Step 2: Identify missing argument

   Here, observe() is called with no arguments, so it will cause an error.

3. Final Answer:

   The observe() method is called without passing the observer class -> Option A

4. Quick Check:

   observe() needs observer class argument [OK]

Hint: Always pass observer class to observe() [OK]

Common Mistakes:

• Calling observe() without arguments
• Renaming boot() incorrectly
• Calling observe() on wrong class

5. You want to log a message every time a Post model is updated, but only if the title has changed. How should you implement this in a PostObserver?

hard

A. Use the deleted(Post $post) method and check if $post->isDirty('title') is true

B. Use the saving(Post $post) method and check if $post->wasChanged('title') is true

C. Use the updated(Post $post) method and check if $post->wasChanged('title') is true

D. Use the created(Post $post) method and check if $post->title is not empty

Solution

1. Step 1: Identify correct event for update

   The updated() method runs after a model is updated, suitable for this task.

2. Step 2: Check how to detect changed attributes

   wasChanged('title') returns true if the title attribute was changed during the update.

3. Step 3: Combine logic

   Inside updated(), check wasChanged('title') to log only when title changed.

4. Final Answer:

   Use the updated(Post $post) method and check if $post->wasChanged('title') is true -> Option C

5. Quick Check:

   updated() + wasChanged('title') detects title changes [OK]

Hint: Use updated() and wasChanged() to detect attribute changes [OK]

Common Mistakes:

• Using created() or deleted() for updates
• Using wasChanged() inside saving() which runs before update
• Checking isDirty() in deleted() event