Call it like this:
            db.add_book(doc_type='book',
            body={'title': 'foobar', '_language': 'it'})

def add_book(self, body, doc_type='book'):
        '''
        Call it like this:
            db.add_book(doc_type='book',
            body={'title': 'foobar', '_language': 'it'})
        '''
        body = validate_book(body)
        body['_insertion_date'] = current_time_millisec()
        return self.es.index(index=self.index_name, doc_type=doc_type, body=body)