#29037: Add a bulk_update method to models
-------------------------------------+-------------------------------------
Reporter: Tom Forbes | Owner: nobody
Type: New feature | Status: new
Component: Database layer | Version: master
(models, ORM) |
Severity: Normal | Resolution:
Keywords: | Triage Stage:
| Unreviewed
Has patch: 0 | Needs documentation: 0
Needs tests: 0 | Patch needs improvement: 0
Easy pickings: 0 | UI/UX: 0
-------------------------------------+-------------------------------------
Description changed by Tom Forbes:
Old description:
> Currently it's not easily or neatly possible to update multiple rows with
> differing values using the ORM. Most people who need to update a number
> of models with a value that's distinct to each model need to issue N
> queries. This is akin to the situation that lead to the addition of
> bulk_create.
>
> Updating multiple rows with differing values in a single query is indeed
> possible in SQL, and Postgres has some specific syntax for it[1]. Other
> databases can use a CASE/WHEN:
>
> {{{#!python
> SomeModel.object.update(
> some_field=Case(
> When(id=1, then=Value('Field value for ID=1')),
> When(id=2, then=Value('Field value for ID=2'))
> )
> )
> }}}
>
> This isn't particularly elegant and cannot take advantage of specific DB
> features (like pg UPDATE FROM), and batching is hard. An API similar to
> bulk_create would be nice:
>
> {{{#!python
> SomeModel.objects.bulk_update(list_of_models, batch_size=100)
> }}}
>
> There is some prior art in the django-bulk-update package[2], which has
> some impressive performance numbers in it's readme.
>
> 1. https://stackoverflow.com/questions/18797608/update-multiple-rows-in-
> same-query-using-postgresql
>
> 2. https://github.com/aykut/django-bulk-update
New description:
Currently it's not easily or neatly possible to update multiple rows with
differing values using the ORM. Most people who need to update a number of
models with a value that's distinct to each model need to issue N queries.
This is akin to the situation that lead to the addition of bulk_create.
Updating multiple rows with differing values in a single query is indeed
possible in SQL, and Postgres has some specific syntax for it[1]. Other
databases can use a CASE/WHEN:
{{{#!python
SomeModel.object.filter(id__in=[1,2]).update(
some_field=Case(
When(id=1, then=Value('Field value for ID=1')),
When(id=2, then=Value('Field value for ID=2'))
)
)
}}}
This isn't particularly elegant and cannot take advantage of specific DB
features (like pg UPDATE FROM), and batching is hard. An API similar to
bulk_create would be nice:
{{{#!python
SomeModel.objects.bulk_update(list_of_models, batch_size=100)
}}}
There is some prior art in the django-bulk-update package[2], which has
some impressive performance numbers in it's readme.
1. https://stackoverflow.com/questions/18797608/update-multiple-rows-in-
same-query-using-postgresql
2. https://github.com/aykut/django-bulk-update
--
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Ticket URL: <https://code.djangoproject.com/ticket/29037#comment:1>
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