Pony.fm/database/migrations/2013_08_01_051337_create_comments.php

<?php

use Illuminate\Database\Migrations\Migration;

class CreateComments extends Migration {
	public function up() {
		Schema::create('comments', function($table){
			$table->increments('id');
			$table->integer('user_id')->unsigned();
			$table->string('ip_address', 46);
			$table->text('content');

			$table->timestamps();
			$table->timestamp('deleted_at')->nullable()->index();

			$table->integer('profile_id')->unsigned()->nullable()->index();
			$table->integer('track_id')->unsigned()->nullable()->index();
			$table->integer('album_id')->unsigned()->nullable()->index();
			$table->integer('playlist_id')->unsigned()->nullable()->index();

			$table->foreign('profile_id')->references('id')->on('users');
			$table->foreign('user_id')->references('id')->on('users');
			$table->foreign('track_id')->references('id')->on('tracks');
			$table->foreign('album_id')->references('id')->on('albums');
			$table->foreign('playlist_id')->references('id')->on('playlists');
		});
	}

	public function down() {
		Schema::table('comments', function($table){
			$table->dropForeign('comments_user_id_foreign');
			$table->dropForeign('comments_track_id_foreign');
			$table->dropForeign('comments_album_id_foreign');
			$table->dropForeign('comments_playlist_id_foreign');
		});
		Schema::drop('comments');
	}
}