ValueError:无法添加*：实例在数据库"default“上，值在数据库"None”上
ValueError:无法添加*：实例在数据库"default“上，值在数据库"None”上
提问于 2011-10-20 21:56:41
In [1]: from editor.models import *
In [4]: from subscriptions.models import *
In [5]: template = StockTemplate.objects.create(name='Template 1')
In [6]: template
Out[6]: <StockTemplate: Template 1>
In [7]: plan = SubscriptionPlan.objects.create(name='Bronze')
In [8]: plan
Out[8]: <SubscriptionPlan: Bronze>
In [12]: plan.templates.add(template)
---------------------------------------------------------------------------
ValueError Traceback (most recent call last)
/home/me/GitProjects/test_git/proj/<ipython console> in <module>()
/home/me/GitProjects/test_git/django-trunk/django/db/models/fields/related.pyc in add(self, *objs)
498 if rel.through._meta.auto_created:
499 def add(self, *objs):
--> 500 self._add_items(self.source_field_name, self.target_field_name, *objs)
501
502 # If this is a symmetrical m2m relation to self, add the mirror entry in the m2m table
/home/me/GitProjects/test_git/django-trunk/django/db/models/fields/related.pyc in _add_items(self, source_field_name, target_field_name, *objs)
558 if not router.allow_relation(obj, self.instance):
559 raise ValueError('Cannot add "%r": instance is on database "%s", value is on database "%s"' %
--> 560 (obj, self.instance._state.db, obj._state.db))
561 new_ids.add(obj.pk)
562 elif isinstance(obj, Model):
ValueError: Cannot add "<StockTemplate: Template 1>": instance is on database "default", value is on database "None"模型
6 class SubscriptionPlan(models.Model):
7 name = models.CharField(max_length=255)
8 templates = models.ManyToManyField(StockTemplate)
9 monthly_fee = models.IntegerField("Monthly Fee", max_length=16, default="0")
10 modified = models.DateTimeField(auto_now=True, editable=False)
11 created = models.DateTimeField(auto_now_add=True, editable=False)
12
13 def __unicode__(self):
14 return "%s" % self.name
18 class StockTemplate(IKImage):
19 name = models.TextField()
20 description = models.TextField(blank=True)
21
22 is_public = models.BooleanField(default=True)
23
24 html = models.FileField(upload_to='stock_templates/html/', \
25 help_text='The file that will be used to render.')
26 #css = models.FileField(upload_to='stock_templates/css/', blank=True)
27
28 img = models.ImageField(upload_to='stock_templates/img/')
29
30 modified = models.DateTimeField(auto_now=True)
31 created = models.DateTimeField(auto_now_add=True)
32
33 objects = StockTemplateManager()
34
35 class IKOptions:
36 spec_module = 'editor.specs'
37 cache_dir = 'stock_templates/img/specs/'
38 image_field = 'img'
39
40 def __unicode__(self):
41 return u"%s" % self.name
42
43 def get_absolute_url(self):
44 return reverse('preview_stock', args=[self.id])这与StockTemplate是IKImage对象的事实有关吗？
回答 2
Stack Overflow用户
回答已采纳
发布于 2011-11-04 01:08:50
这里的问题是，在将模板添加到产品之前，您需要为这两个对象调用方法save：
template.save()
plan.save()
plan.templates.add(template)如果这些对象都没有id (plan和template)，Django就不能添加它。
Stack Overflow用户
发布于 2021-07-13 23:33:22
此错误的一个非常常见的原因是在保存(父)对象之前尝试添加关系。首先，保存对象，然后添加关系。希望这个问题能得到解决。
示例：
a1 = Article(headline='Django lets you build Web apps easily')现在，如果您直接尝试像这样添加关系：
a1.publications.add(p1)它会给出一个错误。
解决方案:先保存它，然后添加关系！！
a1.save()
a1.publications.add(p1)这将会无懈可击。
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原文链接：
https://stackoverflow.com/questions/7837033
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