[英]Django foreign key count filter
我有以下两种模型:
Class Foo(models.model):
param1 = ...
param2 = ...
...
paramN = ...
Class Bar(models.model):
foo = models.ForeignKey(Foo)
...
...
目标:计算所有Foo实例的QuerySet,以便将多个Bar实例连接到它
我一直在寻找解决方案,这似乎对其他所有人都有效
Foo.objects.annotate(num_bar=Count('bar')).filter(num_bar__gt=1)
这给了我一个FieldError
说'bar'
对于Foo
不是一个可能的字段,然后我尝试了'bar_set'
并且也得到了同样的错误
我是否有可能错误地实施它们,或者因为它们很旧而现在已经贬值了? 任何帮助,将不胜感激!
Traceback (most recent call last):
File "<console>", line 1, in <module>
File "/home/ryan/.virtualenvs/project/local/lib/python2.7/site-packages/django/db/models/manager.py", line 127, in manager_method
return getattr(self.get_queryset(), name)(*args, **kwargs)
File "/home/ryan/.virtualenvs/project/local/lib/python2.7/site-packages/django/db/models/query.py", line 794, in annotate
obj.query.add_annotation(annotation, alias, is_summary=False)
File "/home/ryan/.virtualenvs/project/local/lib/python2.7/site-packages/django/db/models/sql/query.py", line 982, in add_annotation
summarize=is_summary)
File "/home/ryan/.virtualenvs/project/local/lib/python2.7/site-packages/django/db/models/aggregates.py", line 20, in resolve_expression
c = super(Aggregate, self).resolve_expression(query, allow_joins, reuse, summarize)
File "/home/ryan/.virtualenvs/project/local/lib/python2.7/site-packages/django/db/models/expressions.py", line 491, in resolve_expression
c.source_expressions[pos] = arg.resolve_expression(query, allow_joins, reuse, summarize, for_save)
File "/home/ryan/.virtualenvs/project/local/lib/python2.7/site-packages/django/db/models/expressions.py", line 448, in resolve_expression
return query.resolve_ref(self.name, allow_joins, reuse, summarize)
File "/home/ryan/.virtualenvs/project/local/lib/python2.7/site-packages/django/db/models/sql/query.py", line 1532, in resolve_ref
self.get_initial_alias(), reuse)
File "/home/ryan/.virtualenvs/project/local/lib/python2.7/site-packages/django/db/models/sql/query.py", line 1471, in setup_joins
names, opts, allow_many, fail_on_missing=True)
File "/home/ryan/.virtualenvs/project/local/lib/python2.7/site-packages/django/db/models/sql/query.py", line 1396, in names_to_path
"Choices are: %s" % (name, ", ".join(available)))
FieldError: Cannot resolve keyword 'bar' into field. Choices are: param1, param2, param3, ..., paramN
我的Django版本是1.8.3
该错误可能有多种原因,我将尝试说明可能的原因:
num_model
。 还检查是否可以得到它们的数量(肮脏的方式:)):
for foo in Foo.objects.all(): if foo.bar_set.count() < 2: #do sth like : foo.bar_set.get() or temp = temp + 1
从您对模型的简短描述(不是您的主代码)开始,找不到其他原因。 您的查询应该可以。
因此,在尝试了很多之后,这是一个可行的解决方案:
Bar.objects.values("foo_id").annotate(Count("foo_id")).filter(pk__count__gt=1)
不能完全确定为什么这样做有效,而另一个则无效,但实际上,它只是获取具有相同foo_id
的Bar
对象的数量,并确保存在多个对象。
如果有人想解释一个可行的原因,而另一个却不可行,那将不胜感激。
由于输入错误,我遇到了同样的问题。 这是我的用例的解决方案
# from django.db.models.sql.aggregates import Count # wrong import
from django.db.models import Count # correct one
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