MySQL INSERT ... ON DUPLICATE KEY UPDATE com Django 1.4 para inserção em massa

class BulkInsertManager(models.Manager):
    def _bulk_insert_or_update(self, create_fields, update_fields, values):

        from django.db import connection, transaction
        cursor = connection.cursor()

        db_table = self.model._meta.db_table

        values_sql = []
        values_data =[]

        for value_lists in values:
            values_sql.append( "(%s)" % (','.join([ "%s" for i in range(len(value_lists))]),) )
            values_data.extend(value_lists)

        base_sql = "INSERT INTO %s (%s) VALUES " % (db_table, ",".join(create_fields))

        on_duplicates = []

        for field in update_fields:
            on_duplicates.append(field + "=VALUES(" + field +")")

        sql = "%s %s ON DUPLICATE KEY UPDATE %s" % (base_sql, ", ".join(values_sql), ",".join(on_duplicates))

        cursor.executemany(sql, [values_data])
        transaction.commit_unless_managed()

class User_Friend(models.Model):
    objects = BulkInsertManager() # assign a custom manager to handle bulk insert

    id = models.CharField(max_length=255)
    user = models.ForeignKey(User, null=False, blank=False)
    first_name = models.CharField(max_length=30)
    last_name = models.CharField(max_length=30)
    city = models.CharField(max_length=50, null=True, blank=True)
    province = models.CharField(max_length=50, null=True, blank=True)
    country =  models.CharField(max_length=30, null=True, blank=True)

def save_user_friends(user, friends):
    user_friends = []
    for friend in friends:

        create_fields = ['id', 'user_id', 'first_name', 'last_name', 'city', 'province', 'country']
        update_fields = ['first_name', 'last_name', 'city', 'province', 'country']

        user_friends.append(
            [
                str(user.id), 
                str(friend['id']),
                friend['first_name'],
                friend['last_name'],
                friend['city'],
                friend['province'],
                friend['country'],
            ]
        )

    User_Friend.objects._bulk_insert_or_update(create_fields, update_fields, user_friends)