public function getQueryableProperties()
    {
        $classMetadata = $this->getObjectManager()
                              ->getClassMetadata($this->getEntityClass());

        $fields = $classMetadata->getFieldNames();
        $alias  = $this->getEntityClassAlias();

        foreach ($fields as $key => &$field) {
            $fieldType = $classMetadata->getTypeOfField($field);
            if (!in_array($fieldType, array('string', 'text'))) {
                unset($fields[$key]);
            } else {
                $field = $alias . '.' . $field;
            }
        }

        return $fields;
    }