Automatically deleting NESTED related rows in Laravel 5.4 (Eloquent ORM) - php

Question

Let's assume I have a Book. This Book has Chapters and those Chapters in this Book have Subchapters.
So I have three models:
Book > Chapter > Subchapter
When I delete the Book ($book->delete();), I also want to delete the related Chapters of this Book and also the related Subchapters of all the Chapters from the Book.
Here (Automatically deleting related rows in Laravel (Eloquent ORM)) I found out about Eloquent Events. Whenever a Book is deleted, before that, the Chapter gets deleted because we hook in:
class Book extends Eloquent
{
public function chapters()
{
return $this->has_many('Chapter');
}
protected static function boot() {
parent::boot();
static::deleting(function($book) {
$book->chapters()->delete();
});
}
}
So I thought, I only have to implement the same code in my Chapter-Model, only exchanging "Book" with "Chapter" and "Chapter" with "Subchapter":
class Chapter extends Eloquent
{
public function subChapters()
{
return $this->has_many('SubChapter');
}
protected static function boot() {
parent::boot();
static::deleting(function($chapter) {
$chapter->subChapters()->delete();
});
}
}
This works fine when I delete a Chapter. All the Subchapters will also be deleted.
When I delete the Book it works fine with the Chapters. All the Chapters will also be deleted.
However it only deletes Chapters when I delete the Book. It does not delete the related Subchapters of the deleted Chapters.
Can anybody help me?

Answer 1

That's because when you delete multiple objects at the same time it doesn't trigger the boot deleting function for each model so you should loop through the objects and delete them one by one:
class Book extends Eloquent
{
public function chapters()
{
return $this->has_many(Chapter::class);
}
protected static function boot() {
parent::boot();
static::deleting(function($book) {
foreach($book->chapters as $chapter){
$chapter->delete();
}
});
}
}
/********************************/
class Chapter extends Eloquent
{
public function subChapters()
{
return $this->has_many(SubChapter::class);
}
protected static function boot() {
parent::boot();
static::deleting(function($chapter) {
foreach($chapter->subChapters as $subChapter){
$subChapter->delete();
}
});
}
}
However my recommendation is to set cascading foreign key relation between the tables so the DBMS is going to delete the related rows automatically, the sample code below shows you how to do it in migration files:
Schema::create('chapters', function (Blueprint $table) {
$table->increments('id');
$table->integer('book_id')->unsigned();
$table->string('title');
$table->timestamps();
$table->foreign('book_id')
->references('id')
->on('books')
->onDelete('cascade')
->onUpdate('cascade');
});
Do the same for subChapters.
Hope It helps...

Answer 2

This is because $book->chapters() will just return an instance of Builder. When you call delete() on the builder it will simply just run the query needed to delete those models and not new them up and then delete them which will mean that the deleting event on the Chapter will never be fired.
To get around this you can do something like:
protected static function boot() {
parent::boot();
static::deleting(function($book) {
$book->chapters->each(function ($chapter) {
$chapter->delete();
});
});
}
Hope this helps!

Answer 3

The correct way to do that is to use onDelete('cascade'). In the chapters table migration:
$table->foreign('book_id')
->references('id')
->on('books')
->onDelete('cascade');
In the subchapters migration:
$table->foreign('chapter_id')
->references('id')
->on('chapters')
->onDelete('cascade');
In this case, you don't need to write any code and all chapters and subchapters will be deleted automatically.