[Django] #30151: last() and [] operator give different results
Django
-----------------------------------------+------------------------
Reporter: NMO13 | Owner: nobody
Type: Uncategorized | Status: new
Component: Uncategorized | Version: 1.11
Severity: Normal | Keywords:
Triage Stage: Unreviewed | Has patch: 0
Needs documentation: 0 | Needs tests: 0
Patch needs improvement: 0 | Easy pickings: 0
UI/UX: 0 |
-----------------------------------------+------------------------
I have a model RSSFeed. To get the last element in my DB, I do:
{{{
RSSFeed.objects.last()
# Output: <RSSFeed: www.sooperarticles.com>
}}}
I slice it to get the first 10 element in the query
{{{
first_ten_feeds = RSSFeed.objects.all()[:10]
}}}
Using first and the bracket operator is consistent:
first_ten_feeds.first()
# Output: <RSSFeed: pressetext News>
first_ten_feeds[0]
# Output: <RSSFeed: pressetext News>
But using last and the bracket operator is not consistent:
{{{
first_ten_feeds[9]
# Output: <RSSFeed: FinanzNachrichten.de: Nachrichten zu IT-
Dienstleistungen>
first_ten_feeds.last()
# Output: <RSSFeed: www.sooperarticles.com>
}}}
Why? I expect to get the same result for last() and [] above.
RSSFeed.objects.last() and first_ten_feeds.last()
seem to give the same result but that does not make sense to me.
I already openend a SO question with the same content:
https://stackoverflow.com/questions/54477472/last-and-operator-give-
different-results
There I was suggested to open a bug.
--
Ticket URL: <https://code.djangoproject.com/ticket/30151>
Django <https://code.djangoproject.com/>
The Web framework for perfectionists with deadlines.
Django
Reporter: NMO13 | Owner: nobody
Type: Uncategorized | Status: new
Component: Uncategorized | Version: 1.11
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 NMO13:
Old description:
> I have a model RSSFeed. To get the last element in my DB, I do:
>
> {{{
> RSSFeed.objects.last()
> # Output: <RSSFeed: www.sooperarticles.com>
> }}}
>
> I slice it to get the first 10 element in the query
>
> {{{
> first_ten_feeds = RSSFeed.objects.all()[:10]
> }}}
>
> Using first and the bracket operator is consistent:
>
> first_ten_feeds.first()
> # Output: <RSSFeed: pressetext News>
> first_ten_feeds[0]
> # Output: <RSSFeed: pressetext News>
>
> But using last and the bracket operator is not consistent:
>
> {{{
> first_ten_feeds[9]
> # Output: <RSSFeed: FinanzNachrichten.de: Nachrichten zu IT-
> Dienstleistungen>
>
> first_ten_feeds.last()
> # Output: <RSSFeed: www.sooperarticles.com>
> }}}
>
> Why? I expect to get the same result for last() and [] above.
>
>
> RSSFeed.objects.last() and first_ten_feeds.last()
>
> seem to give the same result but that does not make sense to me.
>
> I already openend a SO question with the same content:
> https://stackoverflow.com/questions/54477472/last-and-operator-give-
> different-results
> There I was suggested to open a bug.
New description:
I have a model RSSFeed. To get the last element in my DB, I do:
{{{
RSSFeed.objects.last()
# Output: <RSSFeed: www.sooperarticles.com>
}}}
I slice it to get the first 10 element in the query
{{{
first_ten_feeds = RSSFeed.objects.all()[:10]
}}}
Using first and the bracket operator is consistent:
first_ten_feeds.first()
# Output: <RSSFeed: pressetext News>
first_ten_feeds[0]
# Output: <RSSFeed: pressetext News>
But using last and the bracket operator is not consistent:
{{{
first_ten_feeds[9]
# Output: <RSSFeed: FinanzNachrichten.de: Nachrichten zu IT-
Dienstleistungen>
first_ten_feeds.last()
# Output: <RSSFeed: www.sooperarticles.com>
}}}
Why? I expect to get the same result for last() and [] above.
RSSFeed.objects.last() and first_ten_feeds.last() seem to give the same
result but that does not make sense to me.
I already openend a SO question with the same content:
https://stackoverflow.com/questions/54477472/last-and-operator-give-
different-results
There I was suggested to open a bug.
--
--
Ticket URL: <https://code.djangoproject.com/ticket/30151#comment:1>
Django
Reporter: NMO13 | Owner: nobody
Type: Uncategorized | Status: new
Component: Uncategorized | Version: 1.11
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 NMO13:
Old description:
> I have a model RSSFeed. To get the last element in my DB, I do:
>
> {{{
> RSSFeed.objects.last()
> # Output: <RSSFeed: www.sooperarticles.com>
> }}}
>
> I slice it to get the first 10 element in the query
>
> {{{
> first_ten_feeds = RSSFeed.objects.all()[:10]
> }}}
>
> Using first and the bracket operator is consistent:
>
> first_ten_feeds.first()
> # Output: <RSSFeed: pressetext News>
> first_ten_feeds[0]
> # Output: <RSSFeed: pressetext News>
>
> But using last and the bracket operator is not consistent:
>
> {{{
> first_ten_feeds[9]
> # Output: <RSSFeed: FinanzNachrichten.de: Nachrichten zu IT-
> Dienstleistungen>
>
> first_ten_feeds.last()
> # Output: <RSSFeed: www.sooperarticles.com>
> }}}
>
> Why? I expect to get the same result for last() and [] above.
>
>
> RSSFeed.objects.last() and first_ten_feeds.last() seem to give the same
> result but that does not make sense to me.
>
> I already openend a SO question with the same content:
> https://stackoverflow.com/questions/54477472/last-and-operator-give-
> different-results
> There I was suggested to open a bug.
New description:
I have a model RSSFeed. To get the last element in my DB, I do:
{{{
RSSFeed.objects.last()
# Output: <RSSFeed: www.sooperarticles.com>
}}}
I slice it to get the first 10 element in the query
{{{
first_ten_feeds = RSSFeed.objects.all()[:10]
}}}
Using first and the bracket operator is consistent:
{{{
first_ten_feeds.first()
# Output: <RSSFeed: pressetext News>
first_ten_feeds[0]
# Output: <RSSFeed: pressetext News>
}}}
But using last and the bracket operator is not consistent:
{{{
first_ten_feeds[9]
# Output: <RSSFeed: FinanzNachrichten.de: Nachrichten zu IT-
Dienstleistungen>
first_ten_feeds.last()
# Output: <RSSFeed: www.sooperarticles.com>
}}}
Why? I expect to get the same result for last() and [] above.
RSSFeed.objects.last() and first_ten_feeds.last() seem to give the same
result but that does not make sense to me.
I already openend a SO question with the same content:
https://stackoverflow.com/questions/54477472/last-and-operator-give-
different-results
There I was suggested to open a bug.
--
--
Ticket URL: <https://code.djangoproject.com/ticket/30151#comment:2>
Django
-------------------------------------+-------------------------------------
Reporter: NMO13 | Owner: nobody
Type: Bug | Status: closed
Component: Database layer | Version: 1.11
(models, ORM) |
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
Changes (by Tim Graham):
* status: new => closed
* component: Uncategorized => Database layer (models, ORM)
* type: Uncategorized => Bug
* resolution: => invalid
Comment:
As far as I can tell from the code you gave, the slice is operating on an
unordered queryset. There's no guarantee as to what ordering the database
will return. `last()` gives ordering by primary key if the queryset isn't
ordered.
--
Ticket URL: <https://code.djangoproject.com/ticket/30151#comment:3>