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queyrset-refactor: Added error reporting if somebody tries to order by a multi-valued field.

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git-svn-id: http://code.djangoproject.com/svn/django/branches/queryset-refactor@7220 bcc190cf-cafb-0310-a4f2-bffc1f526a37
This commit is contained in:
Malcolm Tredinnick 2008-03-11 05:21:50 +00:00
parent 62bdb6eae8
commit 619576002d
3 changed files with 18 additions and 2 deletions
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6
django/db/models/sql/query.py
View File

@ -509,8 +509,10 @@ class Query(object):
pieces = name.split(LOOKUP_SEP) pieces = name.split(LOOKUP_SEP)
if not alias: if not alias:
alias = self.get_initial_alias() alias = self.get_initial_alias()
field, target, opts, joins = self.setup_joins(pieces, opts, alias, result = self.setup_joins(pieces, opts, alias, False, False)
False) if isinstance(result, int):
raise FieldError("Cannot order by many-valued field: '%s'" % name)
field, target, opts, joins = result
alias = joins[-1][-1] alias = joins[-1][-1]
col = target.column col = target.column

7
docs/db-api.txt
View File

@ -541,6 +541,13 @@ primary key if there is no ``Meta.ordering`` specified. For example::
...since the ``Blog`` model has no default ordering specified. ...since the ``Blog`` model has no default ordering specified.
You can only order by model fields that have a single value attached to them
for each instance of the model. For example, non-relations, ``ForeignKey`` and
``OneToOneField`` fields. Explicitly, you can't order by a ``ManyToManyField``
or a reverse ``ForeignKey`` relation. There's no naturally correct ordering
for many-valued fields and a lot of the alternatives are not psosible to
express in SQL very efficiently.
**New in Django development version:** If you don't want any ordering to be **New in Django development version:** If you don't want any ordering to be
applied to a query, not even the default ordering, call ``order_by()`` with no applied to a query, not even the default ordering, call ``order_by()`` with no
parameters. parameters.

7
tests/regressiontests/queries/models.py
View File

@ -418,6 +418,13 @@ FieldError: Infinite loop caused by ordering.
>>> Ranking.objects.all().order_by('rank') >>> Ranking.objects.all().order_by('rank')
[<Ranking: 1: a3>, <Ranking: 2: a2>, <Ranking: 3: a1>] [<Ranking: 1: a3>, <Ranking: 2: a2>, <Ranking: 3: a1>]
# Ordering by a many-valued attribute (e.g. a many-to-many or reverse
# ForeignKey) doesn't make sense (there's no natural ordering).
>>> Item.objects.all().order_by('tags')
Traceback (most recent call last):
...
FieldError: Cannot order by many-valued field: 'tags'
# If we replace the default ordering, Django adjusts the required tables # If we replace the default ordering, Django adjusts the required tables
# automatically. Item normally requires a join with Note to do the default # automatically. Item normally requires a join with Note to do the default
# ordering, but that isn't needed here. # ordering, but that isn't needed here.