raven hamlet
I am trying to write something like this:
somequeryset.order_by("some_field").update(rank="...")
where the "..." is such that all the objects in the queryset have their field "rank" set to a value that is an enumeration of the position of the objects in order determined by the order_by() method. That is, if the order is object_1, object_2, ..., object_n I would like to have their rank field reflect the order, so that object_1.rank = 1, object_2.rank = 2, etc.
Is it possible?
worldly hearth
I am trying to write something like this:
```python
somequeryset.order_by("some_...
Have you looked at the bulk_update method?
raven hamlet
Have you looked at the bulk_update method?
I have. Still, the part of my question about extracting the information about the order and use is to set the rank field on every instance in the queryset, stands.
worldly hearth
I have. Still, the part of my question about extracting the information about th...
Just making sure. I would pull the data out of the database according to your order_by. Then use enumerate to iterate over the collection. Use that index to update the rank for the objects in memory. Then call bulk_update with those updated instances.
To be efficient, you could slim the queryset down with .only('id', 'rank')
raven hamlet
Thanks, so the enumeration would be done in plain Python? There's no ORM/Postgres way to do it?
worldly hearth
Otherwise you might by able to use the RowNumber expression in an annotate with F expressions.
raven hamlet
Otherwise you might by able to use the RowNumber expression in an annotate with ...
Oh that looks dandy!
worldly hearth
And worst case, you can use raw sql
raven hamlet
I guess I'll need to see if any of the two approaches fares much better, benchmark-wise.
worldly hearth
You're right to avoid pulling it into python if possibile. But if it's a large dataset, things might get hairy updating that much data.
raven hamlet
true that. Thanks very much, that helped!
worldly hearth
You're welcome. If there's a bug difference between the two let me know. I'm curious now
raven hamlet
@worldly hearth By the way I see you're a mod. Perhaps it would be nice to let posts on these forums be mark-able as "solved my issue". 😁