#19135: Example in "Spanning Multi-valued relationships" is mixed
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Reporter: anonymous | Owner: nobody
Type: Uncategorized | Status: closed
Component: Documentation | Version: 1.4
Severity: Normal | Resolution: invalid
Keywords: | Triage Stage: Unreviewed
Has patch: 0 | Needs documentation: 0
Needs tests: 0 | Patch needs improvement: 0
Easy pickings: 0 | UI/UX: 0
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Changes (by claudep):
* status: new => closed
* resolution: => invalid
Old description:
> '''The example writes:'''
>
> That may sound a bit confusing, so hopefully an example will clarify. To
> select all blogs that contain entries with both "Lennon" in the headline
> and that were published in 2008 (the same entry satisfying both
> conditions), we would write:
>
> Blog.objects.filter(entry__headline__contains='Lennon',
> entry__pub_date__year=2008)
>
> To select all blogs that contain an entry with "Lennon" in the headline
> as well as an entry that was published in 2008, we would write:
>
> Blog.objects.filter(entry__headline__contains='Lennon').filter(
> entry__pub_date__year=2008)
>
> From my understanding, the two examples are mixed up: the first example
> should be for the second explanation and vice versa. First example is a
> union of two sets: filter(setA, setB), the second example is an
> intersection of two sets: filter(setA).filter(setB).
New description:
'''The example writes:'''
That may sound a bit confusing, so hopefully an example will clarify. To
select all blogs that contain entries with both "Lennon" in the headline
and that were published in 2008 (the same entry satisfying both
conditions), we would write:
{{{
Blog.objects.filter(entry__headline__contains='Lennon',
entry__pub_date__year=2008)
}}}
To select all blogs that contain an entry with "Lennon" in the headline as
well as an entry that was published in 2008, we would write:
{{{
Blog.objects.filter(entry__headline__contains='Lennon').filter(
entry__pub_date__year=2008)
}}}
From my understanding, the two examples are mixed up: the first example
should be for the second explanation and vice versa. First example is a
union of two sets: filter(setA, setB), the second example is an
intersection of two sets: filter(setA).filter(setB).
--
Comment:
No, the example is right. The first filter will apply both conditions on
the same join, while the second one will create a separate join for each
condition, hence the results might be larger.
--
Ticket URL: <https://code.djangoproject.com/ticket/19135#comment:2>
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