I have a legacy database that we want to replace, and Django is still new
to us. There are some 40,000 items in the old db, and each item has an
item_number that is not necessarily the primary key; that way, the users
can maintain their own sku number system and we can maintain data integrity
without either of us getting in the other's way. And it also helps
guarantee data integrity as we migrate the data from the old db to our new
db, since Django will assign PK's and manage FKs as it goes, and leave the
item_numbers intact.
I'm running into trouble though, because Django Views and Forms all assume
that, when performing a lookup, the input is going to be a primary key. For
example, I have an item where item.item_number = '515874'. So when I put
that item_number in, Django looks for an item where item.pk = 515874 and
raises a ValidationError--because there is no such item. The actual PK for
item '515874' is 41293. So I need to take the user's input, use it to get
the right item based on its item_number, and give it back to Django to use
instead.
CreateView and {{ form.as_table }} default to populating a dropdown, which
would mean that the whole item_num/pk problem would go away... but with
Django querying *all* 40,000 items, the page literally took 20 seconds to
load. So the users are going to need to type in item_numbers which I'll
have to convert to PKs.
Overriding form_valid() and clean() weren't working, because the
no-such-item ValidationError had already been raised before either method
could be called. Defining a custom field and overriding that field's
validate method seems to be the right way to go, but I'm still running into
issues. The validate method is being called and is returning the correct
value, but Django seems to be throwing it away. When I step through it with
the debugger, I see the item where (item.id = 41293 and item.item_number =
'515874') is correctly being returned. But when Django calls clean() next,
that item is nowhere to be found and it's busy cleaning '515874', which was
the original input. And then it breaks.
This particular view/ModelForm is a simple tool for non-programmers to be
able to evaluate a small part of a background process.
class ItemsTestCollection(models.Model):
"""An item to be tested in Box Opt."""
item = models.ForeignKey('item.Item', on_delete=models.CASCADE)
qty = models.IntegerField()
case = models.ForeignKey('EvaluateTestCase', on_delete=models.CASCADE)
box = models.ForeignKey('BoxResults', on_delete=models.CASCADE, null=True)
class ItemNumField(forms.CharField):
def validate(self, value):
# item = Item.objects.get(item_number=value)
# value = item.id
# return value
return Item.objects.get(item_number=value)
class AddItem(forms.ModelForm):
item = ItemNumField()
class Meta:
model = ItemsTestCollection
fields = ['item', 'qty', 'case']
class AddItemsToEvaluateCreateView(CreateView):
model = ItemsTestCollection
form_class = AddItem
template_name = 'utils\evaluate.html'
def get_queryset(self):
return ItemsTestCollection.objects.filter(case_id=self.kwargs['pk'])
def get_object(self, queryset=None):
return EvaluateTestCase.objects.get(pk=self.kwargs['pk'])
def get_success_url(self):
if 'add_more' in self.request.POST:
return reverse('utils:evaluate', kwargs={'pk': self.kwargs['pk']})
elif 'optimize' in self.request.POST:
return reverse('utils:results', kwargs={'pk': self.kwargs['pk']})
else:
return '/'
def get_context_data(self, **kwargs):
context = super().get_context_data()
context['case_id'] = self.kwargs['pk']
context['items_in_order'] =
ItemsTestCollection.objects.filter(case_id=self.kwargs['pk'])
return context
ValueError at /utils/box-optimization/add-items/118
Cannot assign "'515874'": "ItemsTestCollection.item" must be a "Item" instance.
Request Method: POST
Request URL: http://localhost:8000/utils/box-optimization/add-items/118
Django Version: 2.0.5
Exception Type: ValueError
Exception Value:
Cannot assign "'515874'": "ItemsTestCollection.item" must be a "Item" instance.
Exception Location:
C:\miniconda3\envs\django\lib\site-packages\django\db\models\fields\related_descriptors.py
in __set__, line 197
Python Executable: C:\miniconda3\envs\django\python.exe
Python Version: 3.6.5
Python Path:
['C:\\WMS Repository\\Warehouse Management System',
'C:\\Program Files\\JetBrains\\PyCharm 2017.3.3\\helpers\\pydev',
'C:\\WMS Repository\\Warehouse Management System',
'C:\\Program Files\\JetBrains\\PyCharm 2017.3.3\\helpers\\pydev',
'C:\\Users\\heast\\.PyCharm2018.1\\system\\cythonExtensions',
'C:\\miniconda3\\envs\\django\\python36.zip',
'C:\\miniconda3\\envs\\django\\DLLs',
'C:\\miniconda3\\envs\\django\\lib',
'C:\\miniconda3\\envs\\django',
'C:\\Users\\heast\\AppData\\Roaming\\Python\\Python36\\site-packages',
'C:\\miniconda3\\envs\\django\\lib\\site-packages',
'C:\\Program Files\\JetBrains\\PyCharm '
'2017.3.3\\helpers\\pycharm_matplotlib_backend']
Server time: Mon, 16 Jul 2018 15:46:11 -0400
Environment:
Request Method: POST
Request URL: http://localhost:8000/utils/box-optimization/add-items/118
Django Version: 2.0.5
Python Version: 3.6.5
Installed Applications:
['item.apps.ItemConfig',
'inventory.apps.InventoryConfig',
'fulfillment.apps.FulfillmentConfig',
'manifest.apps.ManifestConfig',
'order.apps.OrderConfig',
'utils.apps.UtilsConfig',
'django.contrib.admin',
'django.contrib.auth',
'django.contrib.contenttypes',
'django.contrib.sessions',
'django.contrib.messages',
'django.contrib.staticfiles']
Installed Middleware:
['django.middleware.security.SecurityMiddleware',
'django.contrib.sessions.middleware.SessionMiddleware',
'django.middleware.common.CommonMiddleware',
'django.middleware.csrf.CsrfViewMiddleware',
'django.contrib.auth.middleware.AuthenticationMiddleware',
'django.contrib.messages.middleware.MessageMiddleware',
'django.middleware.clickjacking.XFrameOptionsMiddleware']
Traceback:
File
"C:\miniconda3\envs\django\lib\site-packages\django\core\handlers\exception.py"
in inner
35. response = get_response(request)
File
"C:\miniconda3\envs\django\lib\site-packages\django\core\handlers\base.py"
in _get_response
128. response = self.process_exception_by_middleware(e,
request)
File
"C:\miniconda3\envs\django\lib\site-packages\django\core\handlers\base.py"
in _get_response
126. response = wrapped_callback(request, *callback_args,
**callback_kwargs)
File
"C:\miniconda3\envs\django\lib\site-packages\django\views\generic\base.py"
in view
69. return self.dispatch(request, *args, **kwargs)
File
"C:\miniconda3\envs\django\lib\site-packages\django\views\generic\base.py"
in dispatch
89. return handler(request, *args, **kwargs)
File
"C:\miniconda3\envs\django\lib\site-packages\django\views\generic\edit.py"
in post
172. return super().post(request, *args, **kwargs)
File
"C:\miniconda3\envs\django\lib\site-packages\django\views\generic\edit.py"
in post
141. if form.is_valid():
File "C:\miniconda3\envs\django\lib\site-packages\django\forms\forms.py" in
is_valid
179. return self.is_bound and not self.errors
File "C:\miniconda3\envs\django\lib\site-packages\django\forms\forms.py" in
errors
174. self.full_clean()
File "C:\miniconda3\envs\django\lib\site-packages\django\forms\forms.py" in
full_clean
378. self._post_clean()
File "C:\miniconda3\envs\django\lib\site-packages\django\forms\models.py"
in _post_clean
396. self.instance = construct_instance(self, self.instance,
opts.fields, opts.exclude)
File "C:\miniconda3\envs\django\lib\site-packages\django\forms\models.py"
in construct_instance
60. f.save_form_data(instance, cleaned_data[f.name])
File
"C:\miniconda3\envs\django\lib\site-packages\django\db\models\fields\__init__.py"
in save_form_data
838. setattr(instance, self.name, data)
File
"C:\miniconda3\envs\django\lib\site-packages\django\db\models\fields\related_descriptors.py"
in __set__
197. self.field.remote_field.model._meta.object_name,
Exception Type: ValueError at /utils/box-optimization/add-items/118
Exception Value: Cannot assign "'515874'": "ItemsTestCollection.item" must
be a "Item" instance.
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