Django: reorder by model IDs

orderer.py

from typing import Type, List

from django.db import models, connection


class OrdererByID:
    """Helper class to update rows in table according to order of list of IDs provided."""

    def __init__(self, *, model: Type[models.Model], field_name: str) -> None:
        self.reorder_query = f"""
            UPDATE "{model._meta.db_table}"
            SET "{field_name}" = "input_data"."order"
            FROM (
              SELECT
                unnest(%s) AS id,
                unnest(%s) AS order
            ) AS "input_data"
            WHERE ("{model._meta.db_table}"."id" = "input_data"."id")
        """

    def update_order(self, ids: List[str], *, start_from: int = 1) -> int:
        if not ids:
            return 0

        with connection.cursor() as cursor:
            cursor.execute(self.reorder_query, [ids, list(range(start_from, start_from + len(ids)))])
            return cursor.rowcount


class SomeModel(models.Model):
    ...
    order = models.IntegerField()  # this field can be vary
    ...


orderer = OrdererByID(model=SomeModel, field_name='order')
orderer.update_order([5, 2, 7, 3, 4])

# ... leads to followign result in DB:
# [
#     SomeModel(id=5, order=1),
#     SomeModel(id=2, order=2),
#     SomeModel(id=7, order=3),
#     SomeModel(id=3, order=4),
#     SomeModel(id=4, order=5),
# ]

# You may need to refresh objects from DB or just update attrs
# (not implemented in this snippet)