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.
Related
In my Django app, I want to insert a record with a composite primary key. Apparently this should be possible by making use of "unique_together". I'm quite sure this code was working in the past, but for some reason it does not seem to be working now. This code used to run on a Linux VM, and now I'm hosting it in Google App Engine. However I don't see how this can be the cause for this error.
class TermsAndConditionsDocument(models.Model):
organization = models.ForeignKey(Organization, on_delete=models.CASCADE, verbose_name=_("Organization"))
language = models.CharField(_('Language'),choices=LANGUAGE_CHOICES, max_length=5, help_text=_("The language of the content."))
content = models.TextField()
class Meta:
unique_together = ('organization', 'language')
The error:
IntegrityError at /transactions/settings/terms_and_conditions
null value in column "id" violates not-null constraint
DETAIL: Failing row contains (null, nl-BE, <p>B</p>, 10).
According to what I've read, using "unique_together" should cause Django to not need or include an ID as primary key. I checked the database, and the ID field DOES exist. I do not understand where the database constraint and the ID field are still coming from?
Apparently, as pointed out in the comments, a primary key "id" field is always added, even if you don't need it. It's supposed to get out of your way, so you don't even notice its existence. In my case, it required me to give it a value when I created a new record, which is not how things are supposed to work.
A while back I migrated this database from one Postgres database to another Postgres database. I used an SQL dump and load method for this. Some sequences seem to have been lost during that migration.
Because there are no sequences, some fields now lacked autoincrement capabilities, explaining the IntegrityError on insertion.
In order to fix this, I did the following:
1) Export the current data:
manage.py dumpdata > data.json
2) Drop your database and create a new empty one.
3) Run database migrations:
manage.py migrate
4) Load the data again, excluding some default data already recreated by Django.
manage.py loaddata --exclude auth.permission --exclude contenttypes data.json
This procedure seems to have recreated the sequences while also keeping the data.
The unique_together only creates a DB constraint (https://docs.djangoproject.com/en/2.2/ref/models/options/#unique-together).
You could create a custom primary key with the option primary_key https://docs.djangoproject.com/en/2.2/ref/models/fields/#django.db.models.Field.primary_key but you could only do that for one field.
But I suggest to just keep the auto increment id field, this works better with Django.
For the error are you saving a model? or doing a raw import?
I have a model that have a URLField field and I need to make a migration that turns this field into a foreign key, where the string is a unique field of the other object, and, if the object does not exist create it.
for example, turn this:
class Event_UserVisit(Event_Base):
dest_url = models.URLField(max_length=1000)
into this:
class Event_UserVisit(Event_Base):
dest_url = models.ForeignKey(Page)
I've never done a manual migration like this and didn't find any tutorial or instructions to do something like this.
obviously doing a naive migration return errors like this:
django.db.utils.ProgrammingError: column "source_url_id" cannot be cast automatically to type integer
what's the best approach to do it?
note: I need to do this on a production db with lots of data, so I can't have long down time and can't lose any data.
thanks! :)
I don't think you can do this at the ORM level in one go (unless someone corrects me) You would need create a new FK maybe dest_url2 run migrations, then write a script to migrate the data. Next,delete dest_url again run migrations. Then rename dest_url2 to dest_url Django will detect the name change here.
However, I don't understand why you are linking an FK ID on page to a field called dest_url. A PK in Page should not be a 1000 max URL! It has no order and would make indexing hard and slow down your app. It would make more sense do have...
class Event_UserVisit(Event_Base):
page = models.ForeignKey(Page, related_name='eventvisits')
The I assume Page looks something like this...
class Page(models.Model):
dest_url = models.URLField(max_length=1000)
This is a follow-up question on Delete field from standard Django model. In short: a field can be dynamically deleted from a model that is already created, in this case the field User.email . So field email would be deleted from User without changing the code for User. See code below for example.
I can dynamically delete a a field from a model(1), but that happens when the server starts and is undone when it exists. Since syncdb doesn't require the server to be running, and generally seems to ignore the deletion code (somehow), this approach doesn't prevent the field from appearing in the database(2).
Is there a way to do delete the field from the model (without changing the file it's in, as it's a Django model), in a way that also makes it not appear in the database?
Thanks in advance!
Mark
EDIT: I problem is not that I am deleting the text "m = models.IntegerField()" from the model file and want the field removed from the database. The problem is that I am using the code below to remove a field from a model that has already been declared in another file. I do not think that creating a migration with South for every time I run syncdb is a solution(3).
Additional information:
1) Currently, the code is in models.py, but I suppose Where to put Django startup code? works.
2) I can delete it on post_syncdb signal with custom query, but I hope for something more elegant... Or elegant at all, more accurately.
3) If it even works at all, because obviously syncdb is still seeing the 'removed' field), so I think South would to as it's still somehow there.
This is the code (models.py):
class A(models.Model):
m = models.IntegerField()
for i, f in enumerate(A._meta.fields):
if f.name == 'm':
del A._meta.fields[i]
break
class B(A):
n = models.IntegerField()
for i, f in enumerate(B._meta.fields):
if f.name == 'm':
del B._meta.fields[i]
break
EDIT: I checked (with print) and the deletion code is executed on syncdb. It is executed before tables are created
django does a lot of meta class magic and i would guess that the meta class is responsible for defining the database table to back your model. Subsequently just deleting the field is not enough to alter the generated table.
as several people have pointed out, south is the way to deal with these problems.
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()
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?