My problem is as follows:
I am implementing a labeling system for a machine learning problem.
So in short: A complex object should get a simple label information (like a tag).
There should be just one label per object and the set of labels is limited and static.
(e.g.: I want to label all attributs of one animal objects to the information CAT, DOG, etc.)
So I have an item object. I want to save this as a tupel with one of my label-objects (myAnimal, label). This object should only carry ONE information (e.g. DOG). How can I accomplish that?
I thought of an object that holds some booleans and the one boolean I want gets set, but that seems to be not a nice solution since multiple booleans could be set.
I googled for a simple enum-like solution but found nothing satisfying.
It would be nice if you could help me out here ;)
Since your labels are static and pre-defined:
TAGS = ((1,'DOG'),(2,'CAT'),(3,'HORSE')) # and so on
class MyThing(models.Model):
name = models.CharField(max_length=200)
tag = models.IntegerField(choices=TAGS)
With this model, your thing can only have one tag, and you can get the associated tag for your object thus:
foo = MyThing.objects.order_by('?')[0] # get some random object
print 'My object is a ',foo.get_tag_display()
What about a simple model with some relations ?
class LabeledItem(models.Model):
my_object= models.OneToOneField(Item)
label = models.CharField()
The label property could also be a OneToOneField to for example a Label model which has a name as field property.
Related
I haven't had much luck finding other questions that helped with this, but apologies if I missed something and this is a duplicate.
I'm trying to add to some ManyToMany fields, without having to explicitly type out the names of the fields in the code (because the function I'm working on will be used to add to multiple fields and I'd rather not have to repeat the same code for every field). I'm having a hard time using ._meta to reference the model and field objects correctly so that .add() doesn't throw an "AttributeError: 'ManyToManyField' object has no attribute 'add'".
This is simplified because the full body of code is too long to post it all here, but in models.py, I have models defined similar to this:
class Sandwich(models.Model):
name = models.CharField(max_length=MAX_CHAR_FIELD)
veggies = models.ManyToManyField(Veggie)
meats = models.ManyToManyField(Meat)
class Veggie(models.Model):
name = models.CharField(max_length=MAX_CHAR_FIELD)
class Meat(models.Model):
name = models.CharField(max_length=MAX_CHAR_FIELD)
Once instances of these are created and saved, I can successfully use .add() like this:
blt = Sandwich(name='blt')
blt.save()
lettuce = Veggies(name='lettuce')
lettuce.save()
tomato = Veggies(name='tomato')
tomato.save()
bacon = Meat(name='bacon')
bacon.save()
blt.veggies.add(lettuce)
blt.veggies.add(tomato)
blt.meats.add(bacon)
But if I try to use ._meta to get blt's fields and add to them that way, I can't. ie something like this,
field_name='meats'
field = blt._meta.get_field(field_name)
field.add(bacon)
will throw "AttributeError: 'ManyToManyField' object has no attribute 'add'".
So, how can I use ._meta or a similar approach to get and refer to these fields in a way that will let me use .add()? (bonus round, how and why is "blt.meats" different than "blt._meta.get_field('meats')" anyway?)
Why do you want to do
field = blt._meta.get_field(field_name)
field.add(bacon)
instead of
blt.meats.add(bacon)
in the first place?
If what you want is to access the attribute meats on the blt instance of the Sandwich class because you have the string 'meats' somewhere, then it's plain python you're after:
field_string = 'meats'
meats_attribute = getattr(blt, field_string, None)
if meats_attribute is not None:
meats_attribute.add(bacon)
But if your at the point where you're doing that sort of thing you might want to revise your data modelling.
Bonus round:
Call type() on blt.meats and on blt._meta.get_field(field_name) and see what each returns.
One is a ManyToManyField, the other a RelatedManager. First is an abstraction that allows you to tell Django you have a M2M relation between 2 models, so it can create a through table for you, the other is an interface for you to query those related objects (you can call .filter(), .exclude() on it... like querysets): https://docs.djangoproject.com/en/4.1/ref/models/relations/#django.db.models.fields.related.RelatedManager
As the title suggests, what would be the best way to go about adding a third attribute to Django's model enum choice so that I could access the property in the same manner as value or label. For instance, let's call this third attribute text
what I want:
class Vehicle(models.Model):
class VehicleType(??):
HONDA_CIVIC = 1, _("New car"), _("Vroom vroom")
FORD_MODEL_T = 2, _("Old car"), _("not so fast")
type = models.IntegerField(choices=VehicleType.choices, default=VehicleType.FORD_MODEL_T)
vehicle = Vehicle.objects.create()
vehicle.type.text
>>> not so fast
Is this possible without overwriting the base ChoicesMeta? I've tried a version as outlined in the python enum docs by updating __new__ however this doesn't seem to work. (And yes, I know I could change it to models.TextChoices and nix the int value, but I'm curious if this is easily possible)
I have some Django models that record people's listening habits (a bit like Last.fm), like so:
class Artist(models.Model):
name = models.CharField()
class Song(models.Model):
artist = models.ForeignKey(Artist)
title = models.CharField()
class SongPlay(models.Model):
song = models.ForeignKey(Song)
user = models.ForeignKey(User)
time = models.DateTimeField()
class User(models.Model):
# doesn't really matter!
I'd like to have a user page where I can show the top songs that they've listened to in the past month. What's the best way to do this?
The best I've come up with so far is:
SongPlay.past_month
.filter(user=user)
.values('song__title', 'song__id', 'song__artist__name')
.annotate(plays=Count('song'))
.order_by('-plays')[:20]
Above, past_month is a manager that just filters plays from the last month. Assume that we've already got the correct user object to filter by as well.
I guess my two questions are:
How can I get access to the original object as well as the plays annotation?
This just gives me certain values, based on what I pass to values. I'd much rather have access to the original object – the model has methods I'd like to call.
How can I group from SongPlay to Artist?
I'd like to show a chart of artists, as well as a chart of songs.
You can use the same field in both values and annotate.
You have the primary key of the Song object (you could just use song instead of song__id), so use
Song.objects.get(id=...)
For your second question, do a separate query with song__artist as the field in values and annotate:
from django.db.models import Count
SongPlay.past_month
.filter(user=user)
.values('song__artist')
.annotate(plays=Count('song__artist'))
.order_by('-plays')[:20]
agf has already showed you how to group by song_artist. What I would do to get the actual Song object is store it in memcached, or if the method you are calling is rather simplistic make it a static method or a class method. You might could also initialize a Song object with the data from the query and not actually save it to get access to this method. Might help to know the details of the methods you want to call from the Song object.
I want to create an object in Django before calling the save method. This object will be created from a ForeignKey Value, I've changed the foreignkey field to look like an input field in order to write a value instead of selecting it.
I have 2 classes in 2 different model files
class Category(models.Model):
title = models.ForeignKey(Title, verbose_name="Title")
and
class Title(models.Model):
title = models.CharField("Title", primary_key=True, max_length=200)
When I create a category, I have to pick or write a title that already exists in the database and when I try to create a category with a new title I get this error :
Select a valid choice. That choice is not one of the available choices.
What I want to do is creating a title based on what I write in the ForeignKey field before creating the category so it can be used immediately.
I tried to redefine the save method to save the title object before saving the category but it didn't work.
Any help will be really appreciated.
Thank you
The save is performed after the form validation, you can make the category obj creation during the validation.
Have a look at the form fields' clean methods that you can override on django docs http://docs.djangoproject.com/en/dev/ref/forms/validation/#cleaning-and-validating-fields-that-depend-on-each-other
Thank you for your code, I've just tested it. But it's not exactly what I'm looking for, I will explain what I want to do.
Let's say that we have Category and Article classes in our model, each one has a title. To make this title reusable, I created another application that will manage fields, I created the class Title and I added it as foreignkey to Category and Article forms.
I switched the select box to an input field using raw_id_fields.
Now, when I create a category or an article, I have to select or write a title, when this title exists, it works perfectly but when it doesn't exist I want to create it before creating the category so it can use it.
I tried to do that in the save method, in the pre_save signal and in the clean method but I always get the error "Select a valid choice. That choice is not one of the available choices."
I'm using a hard coded solution to create the title now, I want just to see if it will work, these are the lines that I inserted in the different methods to create the title before creating the category :
t = Title(title = "MyTitle")
t.save()
I tried to create a Category with MyTitle as title but I get the same error, when I try to create another one using an existing title, it works and the title "MyTitle" is created. That's mean that the creation of the object happens after the form verification. What I want is just doing this before. The title object should be created before the verification.
Thank you very much for your help
You should probably consider putting the code to create Category entries in the model's manager:
class CategoryManager(Manager):
def create_category(category, title):
t = Title.objects.get_or_create(title=title)
return self.create(title=t)
class Category(models.Model):
title = models.ForeignKey(Title, verbose_name="Title")
objects = CategoryManager()
Then use create_category every time you want to create a Category.
I am currently using Django forms with the Google App Engine and I have a model which is as follows:
class Menu(db.Model):
name = db.StringProperty(required=True)
is_special = db.BooleanProperty()
menu_items = db.ListProperty(MenuItem)
I have a MenuForm which is the following:
class MenuForm(djangoforms.ModelForm):
class Meta:
model = Menu
exclude = ['added_by','menu_items']
When I run this I get the following error:
Exception Type: ValueError
Exception Value: Item type MenuItem is not acceptable
I want to crate the form and have it omit the menu_items property as for one I don't think there is an in built control for the multiple choice, like a group of check boxes. Either way I cannot understand with this property in the exclude items why it is throwing this error.
TIA
Andrew
Your problem comes well before the "create a form" task begins: ListProperty does not allow a list of model entities (although I can't find this clearly documented in the app engine docs, I'm still looking in the docs for a good, clear, unambiguous statement about that). Try changing it into (say) a list of strings, and you'll see everything works (I believe a dropdown is what you get if you don't exclude such a property).
Edit: found the spot in the docs where the issue is mentioned, although it's quaintly phrased -- quoting with added emphasis:
The list can contain values of any of
the value types supported by the
datastore.
...point is, you can have in the list objects of any of the value types... not reference ones, i.e., entities that are instances of some model.
Could you use a list of key strings, instead...?