protected function _generateMigrationFile($version, $contentUp = "", $contentDown = "")
    {
        $classVersion = preg_replace('/[^0-9A-Za-z]/', '', $version);
        $className = 'Migration_' . $classVersion;
        $classData = "<?php

use Phalcon\Migrations\MigrationScript as Migration;

class " . $className . " extends Migration\n" .
            "{\n\n" .
            "\tpublic function up()\n" .
            "\t{\n" . $contentUp .
            "\n\t}" .
            "\n\n" .
            "\tpublic function down()\n" .
            "\t{\n" . $contentDown .
            "\n\t}" .
            "\n}\n";
        $classData = str_replace("\t", "    ", $classData);

        file_put_contents($this->migrationsDir . '/' . $version . '.php', $classData);

        return $classData;
    }