#28211: Inefficient query produced when using OR'ed Q objects
-------------------------------------+-------------------------------------
Reporter: Tom | Owner: nobody
Type: | Status: new
Cleanup/optimization |
Component: Database | Version: 1.10
layer (models, ORM) |
Severity: Normal | Keywords:
Triage Stage: | Has patch: 0
Unreviewed |
Needs documentation: 0 | Needs tests: 0
Patch needs improvement: 0 | Easy pickings: 0
UI/UX: 0 |
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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>
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