cascading-deletes.php

<?php
// I have Groups. A group can have many discussions. A single discussion can have many posts.
// models/Group.php
    public function delete()
    {
        // Check for discussions belonging to the group first
        if ($this->discussions) {
            foreach ($this->discussions as $discussion) {
                $discussion->delete();
            }
        }
        // Remove entry in group_user pivot table
        $this->users()->delete();

        // Now delete the group
        return parent::delete();
    }

// models/Discussion.php
    function delete()
    {
        // Check for posts to discussion first
        if ($this->posts) {
            foreach ($this->posts as $post) {
                $post->delete();
            }
        }
        // Now delete the discussion
        return parent::delete();
    }

// The Post model does pretty much the same as the Discussion model.