If you use timestamps feature in Laravel, then you got the free feature of auto-update on created_at and update_at columns when the model is created or updated. Now, what if you want the same thing for you own customs created_by and updated_by columns? You want them to be automatically updated with the logged in user's id. Well, you can use observer or hook into model's lifecycle in boot or booted methods of the model. Let's use example of Post model as follows:

<?php

namespace App\Models;

use Illuminate\Database\Eloquent\Model;

class Post extends Model
{

    protected static function boot()
    {

        parent::boot();

        // updating created_by and updated_by when model is created
        static::creating(function ($model) {
            if (!$model->isDirty('created_by')) {
                $model->created_by = auth()->user()->id;
            }
            if (!$model->isDirty('updated_by')) {
                $model->updated_by = auth()->user()->id;
            }
        });

        // updating updated_by when model is updated
        static::updating(function ($model) {
            if (!$model->isDirty('updated_by')) {
                $model->updated_by = auth()->user()->id;
            }
        });
    }

}

In the above code, we hook into creating and updating lifecycle of the Post model. This works perfectly and is certainly convenient if you have only few models to apply this feature to. But what if you have many models? You have to apply the above code to all the models. Yes, it will work, but you know, it is not DRY.

The bootable trait, which is also used by Laravel's SoftDeletes trait, can save you a ton in this situation. Laravel' Eloquent model will boot a trait's method with the name of pattern boot[TraitName]. If you take a look into Laravel's source code, you can find the snippet below.

    /**
     * Bootstrap the model and its traits.
     *
     * @return void
     */
    protected static function boot()
    {
        static::bootTraits();
    }

    /**
     * Boot all of the bootable traits on the model.
     *
     * @return void
     */
    protected static function bootTraits()
    {
        $class = static::class;

        $booted = [];

        foreach (class_uses_recursive($class) as $trait) {
            $method = 'boot'.class_basename($trait);

            if (method_exists($class, $method) && ! in_array($method, $booted)) {
                forward_static_call([$class, $method]);

                $booted[] = $method;
            }

        }
    }

The above code tells us the trait with the name of boot[traitName] will also be invoked when the model is booted.

Knowing this, we now can create a new trait called CreatedUpdatedBy with a method of bootCreatedUpdatedBy as follows.

<?php

namespace App\Traits;

trait CreatedUpdatedBy
{
    public static function bootCreatedUpdatedBy()
    {
        // updating created_by and updated_by when model is created
        static::creating(function ($model) {
            if (!$model->isDirty('created_by')) {
                $model->created_by = auth()->user()->id;
            }
            if (!$model->isDirty('updated_by')) {
                $model->updated_by = auth()->user()->id;
            }
        });

        // updating updated_by when model is updated
        static::updating(function ($model) {
            if (!$model->isDirty('updated_by')) {
                $model->updated_by = auth()->user()->id;
            }
        });
    }
}

Next, we can easily use it in any model that we want to apply it to just like when we use SoftDeletes trait. For example in our Post method, it should be looked like this.

<?php

namespace App\Models;

use App\Traits\CreatedUpdatedBy;
use Illuminate\Database\Eloquent\Model;

class Post extends Model
{
    use CreatedUpdatedBy;

}

Whenever the Post model is created or updated, the created_by and/or updated_by will be automatically updated. Cool! Isn't it? 😎

Note that the above is just one example of using bootable traits in the Eloquent model to automatically update created_by and updated_by. However, there are many applications of it. For example, you can use it to automatically delete related models, update slugs, and many others you can think of.