Update 3 (Read This First) :
Yes, this was caused by the object "profile" not having been saved. For those getting the same symptoms, the moral is "If a ForeignKey field seems to be getting set to None when you assign a real object to it, it's probably because that other objects hasn't been saved."
Even if you are 100% sure that it was saved, check again ;-)
Hi,
I'm using content_type / generic foreign keys in a class in Django.
The line to create an instance of the class is roughly this :
tag = SecurityTag(name='name',agent=an_agent,resource=a_resource,interface=an_interface)
Where both agent and resource are content_type fields.
Most of the time, this works as I expect and creates the appropriate object. But I have one specific case where I call this line to create a SecurityTag but the value of the agent field seems to end up as None.
Now, in this particular case, I test, in the preceding line, that the value of an_agent does contain an existing, saved Django.model object of an agent type. And it does.
Nevertheless, the resulting SecurityTag record comes out with None for this field.
I'm quite baffled by this. I'm guessing that somewhere along the line, something is failing in the ORM's attempt to extract the id of the object in an_agent, but there's no error message nor exception being raised. I've checked that the an_agent object is saved and has a value in its id field.
Anyone seen something like this? Or have any ideas?
====
Update : 10 days later exactly the same bug has come to bite me again in a new context :
Here's some code which describes the "security tag" object, which is basically a mapping between
a) some kind of permission-role (known as "agent" in our system) which is a generic content_type,
b) a resource, which is also a generic content_type, (and in the current problem is being given a Pinax "Profile"),
and c) an "interface" (which is basically a type of access ... eg. "Viewable" or "Editable" that is just a string)
class SecurityTag(models.Model) :
name = models.CharField(max_length='50')
agent_content_type = models.ForeignKey(ContentType,related_name='security_tag_agent')
agent_object_id = models.PositiveIntegerField()
agent = generic.GenericForeignKey('agent_content_type', 'agent_object_id')
interface = models.CharField(max_length='50')
resource_content_type = models.ForeignKey(ContentType,related_name='security_tag_resource')
resource_object_id = models.PositiveIntegerField()
resource = generic.GenericForeignKey('resource_content_type', 'resource_object_id')
At a particular moment later, I do this :
print "before %s, %s" % (self.resource,self.agent)
t = SecurityTag(name=self.tag_name,agent=self.agent,resource=self.resource,interface=self.interface_id)
print "after %s, %s, %s, %s" % (t.resource,t.resource_content_type,type(t.resource),t.resource_object_id)
The result of which is that before, the "resource" variable does reference a Profile, but after ...
before phil, TgGroup object
after None, profile, <type 'NoneType'>, None
In other words, while the value of t.resource_content_type has been set to "profile", everything else is None. In my previous encounter with this problem, I "solved" it by reloading the thing I was trying to assign to the generic type. I'm starting to wonder if this is some kind of ORM cache issue ... is the variable "self.resource" holding some kind proxy object rather than the real thing?
One possibility is that the profile hasn't been saved. However, this code is being called as the result of an after_save signal for profile. (It's setting up default permissions), so could it be that the profile save hasn't been committed or something?
Update 2 : following Matthew's suggestion below, I added
print self.resource._get_pk_value() and self.resource.id
which has blown up saying Profile doesn't have _get_pk_value()
So here's what I noticed passing through the Django code: when you create a new instance of a model object via a constructor, a pre-init function called (via signals) for any generic object references.
Rather than directly storing the object you pass in, it stores the type and the primary key.
If your object is persisted and has an ID, this works fine, because when you get the field at a later date, it retrieves it from the database.
However -- if your object doesn't have an ID, the fetch code returns nothing, and the getter returns None!
You can see the code in django.contrib.contenttypes.generic.GenericForeignKey, in the instance_pre_init and __get__ functions.
This doesn't really answer my question or satisfy my curiosity but it does seem to work if I pull the an_agent object out of the database immediately before trying to use it in the SecurityTag constructor.
Previously I was passing a copy that had been made earlier with get_or_create. Did this old instance somehow go out of date or scope?
Related
Can't seem to find much info about this. This is NOT happening in a django test. I'm using DATABASES = { ATOMIC_REQUESTS: True }. Within a method (in mixin I created) called by the view, I'm trying to perform something like this:
def process_valid(self, view):
old_id = view.object.id
view.object.id = None # need a new instance in db
view.object.save()
old_fac = Entfac.objects.get(id=old_id)
new_fac = view.object
old_dets = Detfac.objects.filter(fk_ent__id__exact = old_fac.id)
new_formset = view.DetFormsetClass(view.request.POST, instance=view.object, save_as_new=True)
if new_formset.is_valid():
new_dets = new_formset.save()
new_fac.fk_cancel = old_fac # need a fk reference to initial fac in new one
old_fac.fk_cancel = new_fac # need a fk reference to new in old fac
# any save() action after this crashes with TransactionManagementError
new_fac.save()
I do not understand this error. I already created & saved a new object in db (when I set the object.id to None & saved that). Why would creating other objects create an issue for further saves?
I have tried not instantiating the new_dets objects with the Formset, but instead explicitely defining them:
new_det = Detfac(...)
new_det.save()
But then again, any further save after that raises the error.
Further details:
Essentially, I have an Entfac model, and a Detfac model that has a foreignkey to Entfac. I need to instantiate a new Enfac (distinct in db), as well as corresponding new Detfac for the new Entfac. Then I need to change some values in some of the fields for both new & old objects, and save all that to db.
Ah. The code above is fine.
But turns out, signals can be bad. I had forgotten that upon saving Detfac, there is a signal that goes to another class and that depending on the circumstances, adds a record to another table (sort of an history table).
Since that signal is just a single operation. Something like that:
#receiver(post_save, sender=Detfac)
def quantity_adjust_detfac(sender, **kwargs):
try:
detfac_qty = kwargs["instance"].qte
product = kwargs["instance"].fk_produit
if kwargs["created"]:
initial = {# bunch of values}
adjustment = HistoQuantity(**initial)
adjustment.save()
else:
except TypeError as ex:
logger.error(f"....")
except AttributeError as ex:
logger.error(f"....")
In itself, the fact that THIS wasn't marked as atomic isn't problematic. BUT if one of those exception throws, THEN I get the transactionmanagementerror. I am still not 100% sure why, tough the django docs do mention that when wrapping a whole view in atomic (or any chunk of code for that matter), then try/except within that block can yield unexpected result, because DJango does rely on exception to decide whether or not to commit the transaction as a whole. And the data I was testing with actually threw the exception (type error when creating the HistoQuantity object).
Wrapping the try/exception with a transaction.atomic manager worked however. Guessing that this... removed/handled the throw, thus the outer atomic could work.
Getting around this data store thing that rails provide, I have something that troubles me
Let's say I have a simple post model, with a title, and that for some reason I'd like to store somehow dynamics attributes in another field, call "post_garbage"
In the post model, I have the simple serializer :
class Post < ActiveRecord::Base
serialize :post_garbage
end
As I said, and besides what the rails doc explains, no named accessors are set on this post_garbage field
Playing in the console :
p = Post.first
p.post_garbage["the_stuff"] = "something"
p.save
I get an error, obviously. "the_stuff" is unknown.
Stopping right here, you'd like to dump this data_store thing, safer and easier to create a new field to get the job done (I don't get the utility of it if you have to set an accessor on a data_store field).
* But *
If first an empty hash is saved in this post_garbage field :
p = Post.first
p.post_garbage = {}
p.save
The following becomes possible :
p = Post.first
p.post_garbage["whatever_i_have_in_mind"] = "some value"
p.save
Right after that :
p.post_garbage["it_then_get_dynamic"] = "and that's pretty cool"
p.save
It gets schemaless with no need to specify accessors; kind of provide the expected thing.
So I wonder : many would expect a schemaless thing with the datastore, but it is not said to be used like this by the doc. But it works, with what looks like a bad trick. Wonders…
In the opposite, what's the use of the serialize :post_garbage, if, when empty, it does not returns an empty hash ?
I'd really appreciate some experienced feedback on this one as I feel like I miss something
Thanks a lot
This might have to do with the fact that upon object initialization there is no value in p.post_garbage.
p.post_garbage["the_stuff"] = "something"
Is trying to implicitly treat post_garbage as a hash.
Which would end up being similar to
unset_variable = nil
unset_variable['hash_key'] = 'hash_value'
Using the serialize method for an attribute tells Rails it should expect to condense an Object into a key value map and store it in the database as text. But that doesn't necessarily mean your object is instantiated with this as a hash. It could be any object in particular. But that object needs to be assigned to your attribute before it can be serialized. Serialize may work out the magic to store and reconstitute it on load, but it will not make any assumptions about the form of that object if uninitialized. So without any indication of what object post_garbage is Ruby will not expect it to be a hash.
As for why does it not return an empty has when empty? There is a difference between an empty object and a missing object. (ie: {} vs nil). They are not the same thing, often a missing object is treated like an empty object. But there is value in that distinction, which I expect Rails preserves when loading a serialized attribute.
Perhaps you should try initializing it on create with something like this?
class Post < ActiveRecord::Base
serialize :post_garbage
after_initialize :default_values
private
def default_values
self.post_garbage ||= {}
end
end
I understand that Django want to generate forms automatically so you don't have to do so in your template, and I do understand that many people find it cool.
But I have specific requirements and I have to write my forms on my own. I just need something to parse the data, be it a form submitted using a user interface, or an API request, or whatever.
I tried to use ModelForm, but it doesn't seem to work as I want it to work.
I'd like to have something with the following behavior:
possibility to specify the model of the object I am going to create/update
possibility to specify an object in case of an update
possibility to provide new data in a dictionary
if I am creating a new object, missing fields in my data should be replaced by their default values as specified in my model definition
if I am updating an existing object, missing fields in my data should be replaced by the current values of the object I am updating. Another way of saying is, do not update values that are missing in my data dictionary.
data validation should be performed before calling save(), and it should throw a ValidationError with the list of erroneous fields and errors.
Currently, I prefer to do everything manually :
o = myapp.models.MyModel() # or o = myapp.Models.MyModel.objects.get(pk = data['pk'])
o.field1 = data['field1']
o.field2 = data['field2']
…
o.full_clean()
o.save()
It would be nice to have a shortcut :
o = SuperCoolForm(myapp.models.MyModel, data)
o.save()
Do you know if Django does provide a solution for this or am I asking too much?
Thank you!
I created this field in my model:
numero_str = models.AutoField(primary_key=True, unique=True, default = 0)
The default value seems to invalidate the auto increment of AutoField but if I take it out I receive an error saying that the field can't be null. What I don't understand is: if I declareted it as a AutoField, isn't it supposed to generate a sequencial integer automatically? Or should I declare something when saving an item?
To be more especific, my app is basically a form that is send by e-mail and saved in a database. The error occur when sending (in case I take out the default value). It says:
IntegrityError at /solicitacaodetreinamento/
str_solicitacao.numero_str may not be NULL
I found a solution: I deleted the DB file and all the migration of South (include the Initial). Then I recreated the database and made the migrations. This time, using the default primary key, i.e., "id". In my case it was simpler because I had no real data at all (it is not in production), otherwise I would have to export the data, recreate the database and then import the data. Thank you all.
I have a database of exhibition listings related by foreign key to a database of venues where they take place. Django templates access the venue information in the query results through listing.venue.name, listing.venue.url, and so on.
However, some exhibitions take place in temporary venues, and that information is stored in the same database, in what would be listing.temp_venue_url and such. Because it seems wasteful and sad to put conditionals all over the templates, I want to move the info for temporary venues to where the templates are expecting info for regular venues. This didn't work:
def transfer_temp_values(listings):
for listing in listings:
if listing.temp_venue:
listing.venue = Venue
listing.venue.name = listing.temp_venue
listing.venue.url = listing.temp_venue_url
listing.venue.state = listing.temp_venue_state
listing.venue.location = listing.temp_venue_location
The error surprised me:
ValueError at /[...]/
Cannot assign "<class 'myproject.gsa.models.Venue'>": "Exhibition.venue" must be a "Venue" instance.
I rather thought it was. How do I go about accomplishing this?
The error message is because you have assigned the class Venue to the listing, rather than an instance of it. You need to call the class to get an instance:
listing.venue = Venue()