Pony.fm/database/migrations/2013_08_18_045248_create_favourites.php

<?php

	use Illuminate\Database\Migrations\Migration;

	class CreateFavourites extends Migration {
		public function up() {
			Schema::create('favourites', function($table){
				$table->increments('id');
				$table->integer('user_id')->unsigned()->index();

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

				$table->timestamp('created_at');

				$table->foreign('user_id')->references('id')->on('users')->on_delete('cascade');
				$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('favourites', function($table){
				$table->dropForeign('favourites_user_id_foreign');
				$table->dropForeign('favourites_track_id_foreign');
				$table->dropForeign('favourites_album_id_foreign');
				$table->dropForeign('favourites_playlist_id_foreign');
			});

			Schema::drop('favourites');
		}
	}