how to delete all eloquent child one by one. its hierarchy like category => course => chapter => exams

I have one issue when i delete parent i want to delete all child of from different modal.i want when i delete category delete all course of category and delete all chapter of course and delete all exams of chapter

I have 4 Models [ Category,Course,Chapter,Exam ]

category child is course course child is chapter chapter child is exams

//Category modal 

public function courses()
{
    return $this->hasMany(Course::class);
}

// Course Model 

public function category()
{
    return $this->belongsTo(Category::class);
}


public function chapters()
{
    return $this->hasMany(CourseChapter::class);
}

// Chapter model

public function course()
{
    return $this->belongsTo(Course::class);
}

public function exams()
{
    return $this->hasMany(Exam::class);
}

There are two ways you can do it:

1 - The Migration Way

Inside each of your migrations where you have a foreign key write it like this:

Courses Migration:

$table->foreignId('category_id)->constrained()->cascadeOnDelete();

This will make sure as soon as a category is deleted, all the related courses are deleted. Repeat the same process for rest of them like:

// chapter
$table->foreignId('course_id')->constrained()->cascadeOnDelete();

// exam
$table->foreignId('chapter_id')->constrained()->cascadeOnDelete();

2 - The Model Way

You will need to implement Laravel's cascading delete feature inside each model, here is how you have can implement this:

// Category model
class Category extends Model
{
    public function courses()
    {
        return $this->hasMany(Course::class);
    }

    protected static function boot()
    {
        parent::boot();

        static::deleting(function ($category) {
            $category->courses()->delete();
        });
    }
}

// Course model
class Course extends Model
{
    public function category()
    {
        return $this->belongsTo(Category::class);
    }

    public function chapters()
    {
        return $this->hasMany(Chapter::class);
    }

    protected static function boot()
    {
        parent::boot();

        static::deleting(function ($course) {
            $course->chapters()->delete();
        });
    }
}

// Chapter model
class Chapter extends Model
{
    public function course()
    {
        return $this->belongsTo(Course::class);
    }

    public function exams()
    {
        return $this->hasMany(Exam::class);
    }

    protected static function boot()
    {
        parent::boot();

        static::deleting(function ($chapter) {
            $chapter->exams()->delete();
        });
    }
}

// Exam model
class Exam extends Model
{
    public function chapter()
    {
        return $this->belongsTo(Chapter::class);
    }
}