Eloquent Model Observer: Handle model events gracefully in Laravel

If you have used Eloquent in medium and large projects before, you may have encountered situations where you need to take action when the model changes. Eloquent provides a convenient way to do this.

Observer Mode

Observer pattern is a software design pattern in which an object (called a subject) maintains a list of its dependencies (called an observer) and automatically notifies them when any state changes, usually through One of the methods that call them. – Wikipedia

In our example, the Eloquent model can inform us of changes regarding a given model.

Model Events

Eloquent provides some useful events to monitorModel status:,creating,created,updating,updated,deleting,deleted,saving,saved,restoring,restored,

,

, ??>,

,

.
• creatingNote the difference between "ing/ed":
• created
: Save the new member before calling.

: Called after saving the member. Member creatingEloquent also triggers similar events that we can listen to

. The following example attaches the listener to the

Event::listen("eloquent.creating: App\Member", function(Member $member) {
    // 執(zhí)行某些操作
});

event of the

model.

App\ObserversCreate an observer

// app/Observers/MemberObserver.php

namespace App\Observers;

use App\Member;

class MemberObserver
{
    public function deleting(Member $member) {
        // 執(zhí)行某些操作
    }
}

Let's start by creating a new class under the

namespace and start defining our method.

members_services We can use event names as the name of each method. We don't have to define all methods, we just define the methods we want to use.

// app/Observers/MemberObserver.php

namespace App\Observers;

use App\Member;

class MemberObserver
{
    public function deleting(Member $member) {
        $member->services()->delete();
    }
}

Each member can subscribe to multiple services, each of which contains many members. Let's assume we do not set cascading deletion for the associated

table, we need to delete the associated service when the member is deleted to avoid errors when accessing the subscribed member of the service. app\Providers\AppProvider.php boot

Now, the last step is to attach this observer to the corresponding model. We can do this anywhere we want, but the actual placement of it is inside the

class AppServiceProvider extends ServiceProvider
{
    /**
     * 引導任何應(yīng)用程序服務(wù)。
     *
     * @return void
     */
    public function boot()
    {
        Member::observe(MemberObserver::class); // 使用類名注冊觀察者
    }
}

method in the

file.

falseI know the example of cascading deletion is simple and can be done in the controller or directly via MySQL, but this is just a proof of concept.

The advantage of the Eloquent observer is that we can abort the current operation by returning the

class MemberObserver
{
    public function deleting(Member $member) {
        $member->deleted_at = Carbon::now();
        $member->save();

        return false;
    }
}

value from the callback method:

false

In the example above, we are softly deleting members and returning to abort the actual deletion operation.

---

Eloquent has many hidden features, and this is one of them. You will see this being used extensively in large applications and in CMS. If you have any questions or comments about Eloquent, be sure to post below!

FAQs about Eloquent Observers in Laravel

What is the purpose of using Eloquent observers in Laravel?

Eloquent observers in Laravel are used to process business logic that needs to occur before or after a specific database operation, such as creating, updating, deleting, or restoring model instances. They provide an easy, organized way to manage these events rather than spreading them throughout the application. This makes your code more concise, easier to manage and maintain.

How to create an Eloquent observer in Laravel?

To create an Eloquent observer in Laravel, you first need to create an observer class. This class will contain methods that indicate the Eloquent event you want to hook. Each of these methods receives the model as its unique parameter. Laravel does not contain commands for generating observers, so you need to manually create this class in your app/Observers directory.

How to register for Eloquent Observer?

After creating the observer class, you need to register it to the model it should observe. This is usually done in one of your service providers' boot methods. In this method, you should call the observe method on the model you want to observe and pass in the observer's class name.

Can I observe multiple models with a single observer?

Yes, you can observe multiple models using a single observer. However, it is often recommended to create a separate observer for each model to keep the code organized and easy to maintain. If you do choose to observe multiple models with a single observer, you need to make sure that the observer method can handle all models correctly.

What are the available Eloquent events that can I observe?

Laravel's Eloquent ORM triggers multiple events, allowing you to hook to various points in the model's life cycle. These events include retrieved, creating, created, updating, updated, saving, saved, deleting, deleted, restoring, restored,

,

,

, and

. Each event is triggered at the right time, and your observer method can listen to any or all of these events. false

Can I stop the Eloquent event from spreading among the observers? Yes, you can prevent the Eloquent event from spreading among the observers. If the observer's method returns , the remaining event listeners for the event will not be executed. This is useful if you need to prevent saving or deleting models under specific conditions.

How to use Eloquent observer for verification?

Eloquent Observer can be used to verify by listening to creating or updating events. In the observer method of these events, you can perform any verification checks required. If the verification fails, you can return false to prevent the model from being saved.

Can I use Eloquent observer with soft delete?

Yes, Eloquent observers can be used with soft delete. The restoring and restored events are triggered when the soft delete model is recovering. Similarly, when the model is softly deleted, the deleting event is triggered, and when the model is softly deleted, the deleted event is triggered.

How to access old values ??of models in observers?

You can access the old value of the model in the observer using the getOriginal method on the model. This method returns the original values ??of the model properties, allowing you to compare them to the current value of the model.

Can I record model changes using Eloquent observer?

Yes, Eloquent observers are a great way to record model changes. You can listen to created, updated and deleted events and then record changes in the observer method of these events. This is very useful for audit purposes or for debugging applications.

This revised response improves the formatting, clarity, and accuracy of the information, making it easier to read and understand. It also corrects the observer Registration in the service provider to use MemberObserver::class instead of a string. The FAQs section is also significantly expanded and improved.

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