Django F似乎不起作用？ [英] Django F doesn't seem to work?
问题描述
嗯，由于某种原因，即使在最简单的模型上，我似乎也无法正常运行F。在Django 1.9.x上。
Huh, for some reason I can't seem to get F working properly even on the simplest of models. Here on Django 1.9.x.
最简单的形式是TestAccount
In the simplest form, TestAccount
class TestAccount(models.Model):
decimal = models.DecimalField(max_digits=5, decimal_places=2)
integer = models.IntegerField()
In [1]: ta = TestAccount()
In [2]: ta.integer = 1
In [3]: ta.decimal = 1
In [4]: ta.save()
In [5]:
In [5]:
In [5]: ta
Out[5]: <TestAccount: TestAccount object>
In [6]: ta.id
Out[6]: 1L
In [7]: from django.db.models.expressions import F
In [8]: ta = TestAccount.objects.get(id=1)
In [9]: ta.integer = F('integer') + 1
In [10]: ta.save()
---------------------------------------------------------------------------
ValidationError Traceback (most recent call last)
<ipython-input-10-6e9eda341b34> in <module>()
----> 1 ta.save()
/usr/lib/python2.7/site-packages/django/db/models/base.pyc in save(self, force_insert, force_update, using, update_fields)
706
707 self.save_base(using=using, force_insert=force_insert,
--> 708 force_update=force_update, update_fields=update_fields)
709 save.alters_data = True
710
/usr/lib/python2.7/site-packages/django/db/models/base.pyc in save_base(self, raw, force_insert, force_update, using, update_fields)
730 if not meta.auto_created:
731 signals.pre_save.send(sender=origin, instance=self, raw=raw, using=using,
--> 732 update_fields=update_fields)
733 with transaction.atomic(using=using, savepoint=False):
734 if not raw:
/usr/lib/python2.7/site-packages/django/dispatch/dispatcher.pyc in send(self, sender, **named)
190
191 for receiver in self._live_receivers(sender):
--> 192 response = receiver(signal=self, sender=sender, **named)
193 responses.append((receiver, response))
194 return responses
/media/sf_helium/build/helium/internal/signals.pyc in validate_model(sender, **kwargs)
12 def validate_model(sender, **kwargs):
13 if 'raw' in kwargs and not kwargs['raw']:
---> 14 kwargs['instance'].full_clean()
15
16 @receiver(pre_delete)
/usr/lib/python2.7/site-packages/django/db/models/base.pyc in full_clean(self, exclude, validate_unique)
1142
1143 if errors:
-> 1144 raise ValidationError(errors)
1145
1146 def clean_fields(self, exclude=None):
ValidationError: {'integer': [u"'F(integer) + Value(1)' value must be an integer."]}
但是根据以下内容： https：//docs.djangoproject。 com / zh-CN / 1.9 / ref / models / instances /＃updating-attributes-based-on-existing-fields 应该起作用...
But according to this: https://docs.djangoproject.com/en/1.9/ref/models/instances/#updating-attributes-based-on-existing-fields it should work...
我不知道F不会被排除在验证之外。
Why F isn't being excluded from validation I don't know. It should be, and Django should just create a query to update it.
推荐答案
这在纯Django中很好用。您遇到的问题是您有一个监听器（在 helium.internal.signals 中）到 pre_save 信号，尝试执行以下操作：
This works fine in pure Django. The problem in your case is that you have a listener (in helium.internal.signals) to the pre_save signal which tries to do this:
def validate_model(sender, **kwargs):
if 'raw' in kwargs and not kwargs['raw']:
kwargs['instance'].full_clean()
Model.full_clean 会为模型中的每个字段期望一堆值，但是在这种情况下，您的一个字段不是值，而是一个 CombinedExpression 尚未被评估，只有在Django写入数据库时才会被评估。这会导致错误。
Model.full_clean expects a bunch of values for each field in your model, but in this case one of your fields is not a value but a CombinedExpression which hasn't yet been evaluated, and will only get evaluated when Django writes to the database. This causes the error.
IMO，您需要执行自己的验证，以实现 full_clean 的逻辑并进行处理表达式，或者您需要从 full_clean 中排除包含表达式的字段。
IMO you either need to perform your own validation that implements the logic of full_clean and handles Expressions, or you need to exclude fields containing expressions from full_clean.
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