I'm writing a method in a model and I need to access an attribute from another model.
from django.db import models
class Image(models.Model):
name = models.CharField(max_length=30)
image = models.ImageField(upload_to = slug_path)
def __str__(self):
return "%s %s" % (self.first_name, self.last_name)
def slug_path(self):
# Need Article.slug from Article class here for constructing path
pass
class Article(models.Model):
headline = models.CharField(max_length=100)
pub_date = models.DateField()
reporter = models.ForeignKey(Reporter, on_delete=models.CASCADE)
slug = models.SlugField(max_length=50)
def __str__(self):
return self.headline
I want to write a method in the Image class that will have access to the slug of the Article it is included in via the one to many relation. Is this possible or is there a different way I should be going about this entirely?
Say if only one image can be related to one article, you need to add a field article in the image model which would be foreign key to Article model
article = models.ForeignKey(Article)
Now,
def slug_path(self):
slug = self.article.slug
return slug
Anyway, you can do it in a similar way for many to many fields etc.
Add a relationship to Image corresponding to the Article object, like you did with Article and Reporter.
article = models.ForeignKey(Article, on_delete=models.CASCADE)
Then to get/return the slug:
def slug_path(self):
return self.article.slug
Related
I am making an app that is pretty much similar to google classroom in django.
I have a Course model and an assignment model, and I want to connect an assignment to the specified course.
These are my models
class Assignment(models.Model):
course = models.ForeignKey(Course, on_delete=models.CASCADE)
name = models.CharField(max_length=100)
date_created = models.DateTimeField(default=timezone.now)
class Course(models.Model):
title = models.CharField(max_length=100)
subject = models.CharField(max_length=100)
image = models.ImageField(default='no_course_image.jpg', upload_to='course_images')
owner = models.ForeignKey(User, on_delete=models.CASCADE)
students_invited = models.ManyToManyField(User, null=True, blank=True)
assignments = models.ManyToManyField(Assignment, null=True, blank=True)
date_published = models.DateTimeField(default=timezone.now)
class Meta:
verbose_name_plural = 'Course'
ordering = ['-date_published']
def __str__(self):
return '{} - {}'.format(self.title, self.owner)
But i am getting an error when I specify the course field in the assignment model with the ForeignKey!
Could you please help me with how to connect the assignment to the Course model?
Thank you
ForeignKey is used to setup a many to one relationship. As you are trying to setup a ManyToManyField it won't work in this situation as you can see in the Django documentation
ForeignKey¶
class ForeignKey(to, on_delete, **options)¶
A many-to-one relationship. Requires two positional arguments:
the class to which the model is related and the on_delete option.
In fact you don't even need to set the relation in the Assignment Model as Django will take care of creating a third table linking the two together by their primary keys. You can see this in the documentation
from django.db import models
class Publication(models.Model):
title = models.CharField(max_length=30)
class Meta:
ordering = ['title']
def __str__(self):
return self.title
class Article(models.Model):
headline = models.CharField(max_length=100)
publications = models.ManyToManyField(Publication)
class Meta:
ordering = ['headline']
def __str__(self):
return self.headline
So every time you add the assignment to the course like so
>>> c1 = Course(title='Python Course')
>>> c1.save()
>>> a1 = Assignment(name='Python Assignment')
>>> a1.save()
>>> c1.assignments.add(a1)
And the relation will automatically be created and c1.assignments.all() will return all the assignments linked to the course
If you need to go the other way around then you would use a1.course_set.add(c1). When using the model that doesn't have the ManyToManyField object tied to it you need to use the *_set notation where * will be replaced by the model name in lower case. Can read more about Related Objects references in the docs here
When you try to create the Model Assignment with reference to the model Course, the Course Model has not yet created and vice versa and you will get an error either of the model is not defined
You can use the quotes for it
class Assignment(models.Model):
course = models.ForeignKey('Course', on_delete=models.CASCADE)
name = models.CharField(max_length=100)
date_created = models.DateTimeField(default=timezone.now)
You can use a custom through model enter link description here
I guess the Course model has to be written before the Assignment model.
I'm trying to create a directory of sites, I'm new in Django. What I need is: one site can have many payment processors and one payment processors (Paypal, Payza, etc) can belong to many sites. I'm trying to create a table relationship to represents this. My models are like this:
# Models.py
class Sites(models.Model):
name = models.CharField(max_length=75)
link = models.CharField(max_length=150)
description = models.TextField(blank=True, null=True)
def __str__(self):
return self.name
class PaymentProcessors(models.Model):
name = models.CharField(max_length=75)
def __str__(self):
return self.name
class Sites_PaymentProcessors(models.Model):
site = models.ManyToMany(Sites)
payment_processor = models.ManyToMany(PaymentProcessors)
First, I'd like to know if my models are right. If not, how can I fix it?
Second, I'm using Django Admin site to create the sites and payment processors, how can I populate automatically my Sites_PaymentProcessors table with the relation between Sites and Payment_Processors when I add a new Site?
I would slightly change the models to accomodate ManyToManyFields like this:
class Sites(models.Model):
name = models.CharField(max_length=75)
link = models.CharField(max_length=150)
description = models.TextField(blank=True, null=True)
def __str__(self):
return self.name
class PaymentProcessors(models.Model):
name = models.CharField(max_length=75)
sites = models.ManyToManyField('Sites', related_name='payment_processors')
def __str__(self):
return self.name
Now, if you want custom fields or store more information along with the relationship, you can make use of the through table
For example, if you want to associate the amount limit or something more custom:
class Sites(models.Model):
name = models.CharField(max_length=75)
link = models.CharField(max_length=150)
description = models.TextField(blank=True, null=True)
def __str__(self):
return self.name
class PaymentProcessors(models.Model):
name = models.CharField(max_length=75)
sites = models.ManyToManyField('Sites', related_name='payment_processors', through='SitePaymentProcessor')
def __str__(self):
return self.name
from django.core.validators import MaxValueValidator
class SitePaymentProcessor(models.Model):
site = models.ForeignKey('Site')
payment_processors = models.ForeignKey('PaymentProcessors')
amount_limit = models.IntegerField(default=1000,
validators=[
MaxValueValidator(100)
])
Now, again this is just an example.
Now, registering the admin classes would enable you to populate data into the models via the admin interface.
To auto-populate a large dataset, I would consider using fixtures rather than populating elements individually.
Based on an "Article" model, I'm trying to display a "related content" list in the template by filtering its model field named "category". This "category" field has a ManyToMany relationship to another model named "Category".
It's looks like a very simple task but I can't figure out how to achieve my purpose. By now, a list could be displayed but seems nothing was filtered out.
Below is my DetailView class with a "get_context_data()" method which can product a template tag for displaying a list. Apparently the "F()" class is not the solution.
class ArticleDetail(generic.DetailView):
model = Article
template_name = 'article/detail.html'
def get_context_data(self, **kwargs):
context = super(ArticleDetail, self).get_context_data(**kwargs)
context_related = Article.objects.filter(F('category')).distinct()
context['related'] = context_related
return context
Besides, I also tried to filter with arguments like "category" and "category__exact=F('category')" but still failed.
And here are the models (simplified for question):
class Article(models.Model):
title = models.CharField(max_length=100)
content_text = models.TextField()
category = models.ManyToManyField('Category', blank=True)
def __unicode__(self):
return self.title
class Category(models.Model):
title = models.CharField(max_length=100, unique=True)
def __unicode__(self):
return self.title
No, that's not what F() is for at all.
You don't explain exactly what you do want though. I presume you're looking for other articles in the same categories as the current article. That's easy enough:
Article.objects.filter(category__in=self.object.categories.all())
I have this setup in my models:
class Author(models.Model):
name = models.CharField(max_length=100)
class Topic(models.Model):
name = models.CharField(max_length=100)
class Article(models.Model):
name = models.CharField(max_length=100)
authors = models.ManyToManyField(Author, null=True, blank=True)
topics = models.ManyToManyField(Topic, null=True, blank=True)
Given an author, I want to know which topics he wrote about:
def author_info(request, pk):
author = get_object_or_404(Author, pk=pk)
topics = ????
If I had specified a through field, I could use that, but now Django makes the through field for me, and since its supposed to be transparent, Id rather not reference the field (unless there is a proper Django construction for that).
Use Lookups that span relationships:
topics = Topic.objects.filter(article__authors=author).distinct()
Note: you have to use distinct here, because the same topic can be selected by different articles.
In Django I'm trying to write a ModelForm for a ContactForm and when I try to load the page containing the form it says that it doesn't exist. Then when I try to render the other form I had previously written it says that
Caught AttributeError while rendering: 'CashtextsForm' object has no attribute 'subject'
'Subject' is a field in the form that I was trying to render in ContactForm. So is there some certain order I have to list them in models.py? Here's that code:
# Create your models here.
from django.db import models
from django.forms import ModelForm
class Cashtexts(models.Model):
cashTexts = models.CharField(max_length=100, blank=True) #change me to a website filter
superPoints = models.CharField(max_length=100, blank=True)#chance to "superPoints _Username"
varolo = models.CharField(max_length=100, blank=True)
swagbucks = models.CharField(max_length=100, blank=True)
neobux = models.CharField(max_length=100, blank=True)
topline = models.CharField(max_length=100, blank=True)
Paidviewpoint = models.CharField(max_length=100, blank=True)
cashcrate = models.CharField(max_length=100, blank=True)
def __unicode__(self):
return self.cashcode
class Contact(models.Model):
sender = models.EmailField()
subject = models.CharField(max_length=25)
message = models.TextField()
class CashtextsForm(ModelForm):
class Meta:
model = Cashtexts
def __unicode__(self):
return self.subject
class ContactForm(ModelForm):
class Meta:
model = Contact
I previously had them arranged as Model-Modelform, Model-Modelform but hereit shows them as the way I now currently have them.
Also Is there any advantages to write just forms? Right now I'm more comfortable writing model forms over forms(I dont imagine they are much differnt) but if I only wrote model forms would I be missing out on features? So is there anything I missed on how t write multiple forms in models.py or did I have them written worng? or can i not create them via the command syncdb?
The __unicode__(self) method should be part of your Contact class
class Contact(models.Model):
sender = models.EmailField()
subject = models.CharField(max_length=25)
message = models.TextField()
def __unicode__(self):
return self.subject
It doens't make sense inside CashtextsForm as that does not "know" a subject attribute.
Yes, your form really does not have subject, just remove __unicode__ definition and everything will be ok.
This is because of declarative style of django code. If you want to inspect your objects use pdb module and dir builtin.
You will use ModelForm subclasses almost every time, but sometimes you will need a form which can not be built from model. In this case django will help you to describe such form and to use form clean and field validation.
the subject field is defined in the model and not in the modelform, since a modelform can be initialized without a model instance it is not safe to do something like this:
def __unicode__(self):
return self.instance.subject
What you can do (but I do not really see the point of doing this):
def __unicode__(self):
if getattr(self, 'instance') is not None:
return self.instance.subject
return super(CashtextsForm, self).__unicode__()