#28211: Inefficient query produced when using OR'ed Q objects
-------------------------------------+-------------------------------------
Reporter: Tom | Owner: nobody
Type: | Status: new
Cleanup/optimization |
Component: Database layer | Version: 1.10
(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:
Old description:
> When using OR'ed Q objects in a `.filter()` call Django could be more
> intelligent about the query it produces.
>
> For example, the following two queries both produce `LEFT OUTER JOIN`:
>
> `SomeModel.objects.filter(Q(related_objects__field=1) |
> Q(related_objects__other_field=1)`
>
> `SomeModel.objects.filter(Q(related_objects__field=1) | Q())`
>
> In the case of the second query it could be reduced to a `INNER JOIN` as
> the `OR` is redundant and it is functionally the same as a
> `.filter(related_objects__field=1)`.
>
> It is also quite a common pattern to do:
>
> ```
> filters = Q()
> if condition:
> filters |= Q(x=1)
> if other_condition:
> filters |= Q(y=2)
> ```
>
> And with the current implementation it will always produce a query that
> assumes `filters` is a valid `OR`. Django should/could be more
> intelligent and detect if there is only one `OR` condition, and reduce
> it.
New description:
When using OR'ed Q objects in a `.filter()` call Django could be more
intelligent about the query it produces.
For example, the following two queries both produce `LEFT OUTER JOIN`:
`SomeModel.objects.filter(Q(related_objects__field=1) |
Q(related_objects__other_field=1)`
`SomeModel.objects.filter(Q(related_objects__field=1) | Q())`
In the case of the second query it could be reduced to a `INNER JOIN` as
the `OR` is redundant and it is functionally the same as a
`.filter(related_objects__field=1)`.
It is also quite a common pattern to do:
{{{
filters = Q()
if condition:
filters |= Q(x=1)
if other_condition:
filters |= Q(y=2)
}}}
And with the current implementation it will always produce a query that
assumes `filters` is a valid `OR`. Django should/could be more intelligent
and detect if there is only one `OR` condition, and reduce it.
--
--
Ticket URL: <https://code.djangoproject.com/ticket/28211#comment:1>
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