You can actually set this up in your migrations:

$table->foreign('user_id')->references('id')->on('users')->onDelete('cascade');

Source: http://laravel.com/docs/5.1/migrations#foreign-key-constraints

You may also specify the desired action for the "on delete" and "on update" properties of the constraint:

$table->foreign('user_id')
      ->references('id')->on('users')
      ->onDelete('cascade');

Note: This answer was written for Laravel 3. Thus might or might not works well in more recent version of Laravel.

You can delete all related photos before actually deleting the user.

<?php

class User extends Eloquent
{

    public function photos()
    {
        return $this->has_many('Photo');
    }

    public function delete()
    {
        // delete all related photos 
        $this->photos()->delete();
        // as suggested by Dirk in comment,
        // it's an uglier alternative, but faster
        // Photo::where("user_id", $this->id)->delete()

        // delete the user
        return parent::delete();
    }
}

Hope it helps.

Relation in User model:

public function photos()
{
    return $this->hasMany('Photo');
}

Delete record and related:

$user = User::find($id);

// delete related   
$user->photos()->delete();

$user->delete();

As of Laravel 5.2, the documentation states that these kinds of event handlers should be registered in the AppServiceProvider:

<?php
class AppServiceProvider extends ServiceProvider
{
    /**
     * Bootstrap any application services.
     *
     * @return void
     */
    public function boot()
    {
        User::deleting(function ($user) {
            $user->photos()->delete();
        });
    }

I even suppose to move them to separate classes instead of closures for better application structure.

There are 3 approaches to solving this:

1. Using Eloquent Events On Model Boot (ref: https://laravel.com/docs/5.7/eloquent#events)

class User extends Eloquent
{
    public static function boot() {
        parent::boot();

        static::deleting(function($user) {
             $user->photos()->delete();
        });
    }
}

2. Using Eloquent Event Observers (ref: https://laravel.com/docs/5.7/eloquent#observers)

In your AppServiceProvider, register the observer like so:

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

Next, add an Observer class like so:

class UserObserver
{
    public function deleting(User $user)
    {
         $user->photos()->delete();
    }
}

3. Using Foreign Key Constraints (ref: https://laravel.com/docs/5.7/migrations#foreign-key-constraints)

$table->foreign('user_id')->references('id')->on('users')->onDelete('cascade');

In my case it was pretty simple because my database tables are InnoDB with foreign keys with Cascade on Delete.

So in this case if your photos table contains a foreign key reference for the user than all you have to do is to delete the hotel and the cleanup will be done by the Data Base, the data base will delete all the photos records from the data base.

I would iterate through the collection detaching everything before deleting the object itself.

here's an example:

try {
        $user = user::findOrFail($id);
        if ($user->has('photos')) {
            foreach ($user->photos as $photo) {

                $user->photos()->detach($photo);
            }
        }
        $user->delete();
        return 'User deleted';
    } catch (Exception $e) {
        dd($e);
    }

I know it is not automatic but it is very simple.

Another simple approach would be to provide the model with a method. Like this:

public function detach(){
       try {

            if ($this->has('photos')) {
                foreach ($this->photos as $photo) {

                    $this->photos()->detach($photo);
                }
            }

        } catch (Exception $e) {
            dd($e);
        }
}

Then you can simply call this where you need:

$user->detach();
$user->delete();

Or you can do this if you wanted, just another option:

try {
    DB::connection()->pdo->beginTransaction();

    $photos = Photo::where('user_id', '=', $user_id)->delete(); // Delete all photos for user
    $user = Geofence::where('id', '=', $user_id)->delete(); // Delete users

    DB::connection()->pdo->commit();

}catch(\Laravel\Database\Exception $e) {
    DB::connection()->pdo->rollBack();
    Log::exception($e);
}

Note if you are not using the default laravel db connection then you need to do the following:

DB::connection('connection_name')->pdo->beginTransaction();
DB::connection('connection_name')->pdo->commit();
DB::connection('connection_name')->pdo->rollBack();

yeah, but as @supersan stated upper in a comment, if you delete() on a QueryBuilder, the model event will not be fired, because we are not loading the model itself, then calling delete() on that model.

The events are fired only if we use the delete function on a Model Instance.

So, this beeing said:

if user->hasMany(post)
and if post->hasMany(tags)

in order to delete the post tags when deleting the user, we would have to iterate over $user->posts and calling $post->delete()

foreach($user->posts as $post) { $post->delete(); } -> this will fire the deleting event on Post

VS

$user->posts()->delete() -> this will not fire the deleting event on post because we do not actually load the Post Model (we only run a SQL like: DELETE * from posts where user_id = $user->id and thus, the Post model is not even loaded)