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.
Related
I'm trying to learn Google App Engine's NDB and I'm confused about the structure of models.
My situation is similar to a CMS platform with Post Types (like in WordPress), so I have "Blogs" and "Pages". All of these Post Types require the same set of attributes: Parent, Name, Slug, Template, Content, Status, and Date.
So far, I gather that I need to create a Model for these like this:
class Post(ndb.Expando):
parent = ndb.StringProperty()
name = ndb.StringProperty()
slug = ndb.StringProperty()
template = ndb.StringProperty()
content = ndb.StringProperty(indexed=False)
status = ndb.StringProperty()
date = ndb.DateTimeProperty(auto_now_add=True)
(I'm using Expando because I will be adding "unknown" attributes in my application)
But with this structure, all of my posts (in every Post Type) will be within the same "kind", so queries will take longer (if I'm not mistaken).
How can I create many Models (kinds) with the same attributes?
Do I copy & paste the above Model under different class names?
Is it possible to create new Models dynamically (similar to "Custom Post Types" in WordPress)? Does it work if I use ndb.Key('Blog', blogid) instead of declaring a Model?
Do I create a Model called class PostType(ndb.Model) that stores the "Post Types" and give them ancestors of Posts? (If I'm not mistaken, this would cause problems because updating a Post would "lock" the entire ancestor tree for a second or so)
My primary goal is efficiency. Thanks!
Updates:
As written by Dan and mgilson, adding sub-classes of the main Post class Model is a good way to solve this:
class Post(ndb.Expando):
parent = ndb.StringProperty()
name = ndb.StringProperty()
slug = ndb.StringProperty()
template = ndb.StringProperty()
content = ndb.StringProperty(indexed=False)
status = ndb.StringProperty()
date = ndb.DateTimeProperty(auto_now_add=True)
class Blog(Post):
pass
However, this requires writing the Models statically. Is there a way to accomplish this dynamically (without declaring them as Models beforehand)?
Update:
Following the advice given below, I decided to keep all of my entities under the same kind. I might decide later on to change this to subclasses (separate kinds for each "Post Type") if my queries get messy. Thank you all for your great advice!
How can I create many Models with the same attributes?
You can subclass:
class SpecialPost(Post):
"""Special post type that is a different kind than Post."""
Though it's often easy enough to use the same kind and just add an extra field that represents the kind of post which you can filter on in queries.
Is it possible to create new Models dynamically (similar to "Custom Post Types" in WordPress)? Does it work if I use ndb.Key('Blog', blogid) instead of declaring a Model?
I'm not 100% sure that I understand what you're asking here. You can dynamically create models the same way you can dynamically create classes in python (using type), but you probably don't want to be doing this. Getting those dynamically created models (and keeping track of their names) will probably end up giving you serious headaches.
Basically a simple example of subclassing, which #mgilson mentioned already.
class Post(ndb.Expando):
parent = ndb.StringProperty()
name = ndb.StringProperty()
slug = ndb.StringProperty()
template = ndb.StringProperty()
content = ndb.StringProperty(indexed=False)
status = ndb.StringProperty()
date = ndb.DateTimeProperty(auto_now_add=True)
class Blog(Post):
someint = ndb.IntegerProperty()
blog = Blog(status='new', someint=2)
key = blog.put()
print key.kind()
As for dynamically creating models, from the Model's Constructor doc:
An application won't normally call Model(), but is likely to call the
constructor of a class that inherits from Model. This creates a new
instance of this model, also known as an entity.
Even if possible (I didn't dig too deep inside ndb/models.py to say with certainty that it's not) it doesn't appear a clear thing. Personally I'd stay away from that and instead re-think the need for such dynamically created models.
Hello,
I have bound a ModelForm to one of my model that contains a ForeignKey to another model everything driven by a CreateView. What I want to achieve is to create the model object corresponding to the foreign key if it doesn't exist before the form is overall validated and the final object created in database.
Below the models I use:
class UmsAlerting(models.Model):
alert_id = models.IntegerField(primary_key=True, editable=False)
appli = models.ForeignKey('UmsApplication')
env = models.ForeignKey('UmsEnvironment')
contact = models.ForeignKey('UmsContacts')
custom_rule = models.ForeignKey('UmsCustomRules', null=True, blank=True)
class UmsApplication(models.Model):
appli_id = models.IntegerField(primary_key=True)
trigram_ums = models.CharField(max_length=4L)
class UmsContacts(models.Model):
contact_id = models.IntegerField(primary_key=True)
mail_addr = models.CharField(max_length=100L)
class UmsEnvironment(models.Model):
env_id = models.IntegerField(primary_key=True)
env_name = models.CharField(max_length=5L)
The model bound to the form is UmsAlerting. The model object I want to create if it doesn't exist is UmsContacts. I managed to use the field's clean method in my ModelForm of the contact field and use the get_or_create method like below:
def clean_contact(self):
data = self.cleaned_data['contact']
c, _ = UmsContacts.objects.get_or_create(mail_addr=data)
return c
It perfectly works when the contact is already in the database but when it needs to be created my form return a ValidationError on the contact field saying "This field cannot be null". If I submit the same form a second time without changing anything the UmsAlerting object is well created with no validation error.
My guess is that, for a reason I don't get, when get_or_create is used to create a UmsContacts object it cannot be used to create the new UmsAlerting object. So in clean_contact method the get is working and returns the UmsContacts object but the create part doesn't. It'd be like the UmsContacts object is saved when the whole form is validated but not before as I'd want it to.
Anyone could help me find out what is the problem ? Is using the clean method not the best idea ? Is there another strategy to use to take around this problem ?
Thanks in advance for your help.
It's probably because the object you are creating expects value for contact_id. If you use contact_id field for just setting object id -then you do not have to create it at all. Django takes care of Id's automatically.
Also. field clean method should return cleaned data not object. That creates whole lot more problems on its own.
I am starting to create a webapp using Django and MongoDB. Everything is working fine when I create a model and save it into the Database. Now, I do a "Class.objects.get()" to get the object I need from my DB and I have one field called "media" which is a ListField(). I had tried doing either:
Concert.media.append(list)
or
Concert.media.extend(list)
and then
Concert.save()
This is my "Concert" object in my models.py:
class Concert(models.Model):
main_artist = models.CharField(max_length=50)
concert_id = models.AutoField(primary_key=True)
openers = ListField(EmbeddedModelField('Opener'))
concert_date = models.DateField()
slug = models.SlugField(unique=True)
media = ListField()
And when I go to see the results in does not update the object. No values where saved. If someone can help me I going to give a super cyber fist bump.
Concert is a class, not an instance. You can't save a class. You need to make an instance of the class and save that. Something like
c = Concert()
c.media.append(list)
c.save()
(btw, just as a note, list is a bad variable name because list is a type in python. Never use types as variable names (though everyone is guilty of this at one point or another, including me.))
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'd like to find how to select all objects whose ManyToMany field contains another object. I have the following models (stripped down)
class Category(models.Model):
pass
class Picture(models.Model):
categories = models.ManyToManyField(Category)
visible = models.BooleanField()
I need a function to select all the Pictures in one or more Categories:
def pics_in_cats(cat_ids=()):
pass
BUT it needs to return a QuerySet if possible so that I can do something like:
pics_in_cats((1,2,3)).filter(visible=True)
It could be done by loading all the relevant Category objects and merging their picture_set attributes, but that seems inefficient. I'd also like to avoid falling back to raw SQL if possible.
Thanks in advance
Why write a custom function and not use something like this? (untested)
pics = Picture.objects.filter(categories__in = [1,2,3]).filter(visible=True)