Django db.connection.cursor.fetchone() returns emty result, when raw SQL doesn't

I have method in a cusom QuerySet that performs raw SQL query to database.

class QuerySet(models.query.QuerySet):
    def get_short(self, language_code='en'):
        """Returns shortest name for given language"""
        cursor = connection.cursor()
        cursor.execute('''SELECT t.name FROM translation t, name n
                            WHERE n.id IN (%s)
                            AND t.link_id = n.id
                            AND t.lang_id = %s
                            ORDER BY CHAR_LENGTH(t.name)
                            LIMIT 1''', [','.join(["'%s'" % obj.pk for obj in self]), get_language(language_code).pk])
        name = cursor.fetchone()
        if name:
            return name[0]

But it returns empty result. cursor.fetchone() return None instead of value. Wh开发者_Python百科en I execute raw SQL on the same database:

SELECT t.name FROM translation t, name n
                              WHERE n.id IN ('166','167')
                              AND t.link_id = n.id
                              AND t.lang_id = 40
                              ORDER BY  CHAR_LENGTH(t.name)
                              LIMIT 1

It returns properly value.

Where I wrong? Please, help!

Try without the ", ".join to format your first parameter.

cursor.execute('''SELECT t.name FROM translation t, name n
                            WHERE n.id IN %s
                            AND t.link_id = n.id
                            AND t.lang_id = %s
                            ORDER BY CHAR_LENGTH(t.name)
                            LIMIT 1''', [tuple(obj.pk for obj in self), get_language(language_code).pk])