I want to sort a QuerySet of contacts by a related field. But I do not know how.
I tried it like this, but it does not work.
foundContacts.order_by("classification.kam")
Actually in a template I can access the kam value of a contact through contact.classification.kam since it is a OneToOne relationship.
The (simplified) models look like this:
class Classification(models.Model):
kam = models.ForeignKey(User)
contact = models.OneToOneField(Contact)
class Contact(models.Model):
title = models.ForeignKey(Title, blank=True, null=True)
first_name = models.CharField(max_length=200)
last_name = models.CharField(max_length=200)
It should be:
foundContacts.order_by("classification__kam")
Here is a link for the Django docs on making queries that span relationships: https://docs.djangoproject.com/en/dev/topics/db/queries/#lookups-that-span-relationships
You can also see some examples in the order_by reference:
https://docs.djangoproject.com/en/dev/ref/models/querysets/#django.db.models.query.QuerySet.order_by
as the documentation indicates, it should be used as in queries about related models
https://docs.djangoproject.com/en/3.0/ref/models/querysets/#order-by
foundContacts.order_by("classification__kam")
I've struggled a lot with this problem, this is how I solved it:
contact ordered by "kam" (Classification) field:
show_all_contact = Contact.objects.all().order_by(title__kam)
classification ordered by Users email (no sense in it, but only show how it works):
show_all_clasification = Classification.objects.all().order_by(kam__email)
Related
Given these models:
class Profile(models.Model):
name = models.CharField(max_length=50)
class BlogPost(models.Model):
name = models.CharField(max_length=50)
created_by = models.ForeignKey(Profile, related_name='posts')
class Comment(models.Model):
blog = models.ForeignKey(BlogPost, related_name='comments')
body_text = models.TextField()
created_by = models.ForeignKey(Profile, null=True, blank=True, on_delete=models.SET_NULL)
Given a profile, I want to find all of the blog posts created by that profile, where there are either no comments, or only the creator of the post has commented.
For example:
profile = Profile.objects.get(id={id})
profile.posts.exclude(~Q(comments__created_by=profile))
I thought .exclude(~Q(comments__created_by=profile) would exclude all posts where a comment exists that has been created by someone other than the profile, but that's not working out. (It is finding posts where the created_by is null, and also posts where the profile has commented along with other users - which I'm trying to exclude from the set)
What you need is this:
comments_by_others_in_profile_posts = Comment.objects \
.filter(blog__created_by=profile) \
.exclude(created_by=profile)
profile.posts.exclude(comments=comments_by_others_in_profile_posts)
You can also try it like this (i believe this way it can be a little bit faster, but need to see the queries EXPLAIN output):
profile.posts.exclude(id__in=comments_by_others_in_profile_posts.values_list('blog', flat=True))
Well you were almost there, just need to include the conditions from your instincts. A good way to go about this is to use the django shell and a bunch of test data that matches your permutations. For more complex queries, its a good idea to write a unit test first.
profile.posts.filter(Q(comments__isnull=True)|~Q(comments__created_by=profile, comments__created_by__isnull=False))
Just starting in Python/Django framework so sorry if this is dumb... but i cant find any solution.
class Dealer(models.Model):
name = models.CharField(max_length=200)
contacts = models.ManyToManyField(Contact)
class Contact(models.Model):
name = models.CharField(max_length=200)
dealers = models.ManyToManyField(Dealer)
I have this relation set up however when I run SyncDB it doesnt work. It tells me that Contact is not defined on this line
contacts = models.ManyToManyField(Contact)
Im more familiar with compiled languages. Is there anyway to tell python that the contact class exists, or better yet is there a special syntax im missing for defining this kind of relation.
I dont see a need for a two way ManyToMany in both the models, as they are a M:N relationship (2 way relationship).
Your issue here is, Contact is not defined at the point of execution of this code:
contacts = models.ManyToManyField(Contact)
So You need to wrap it in quotes for it to work
contacts = models.ManyToManyField('Contact')
Documentation on that can be found here
I would recommend the following models:
class Dealer(models.Model):
name = models.CharField(max_length=200)
contacts = models.ManyToManyField('Contact')
class Contact(models.Model):
name = models.CharField(max_length=200)
and It would do exactly what you are looking for.
You can read about ManyToMany relationships here. The same link also covers how to handle Reverse m2m queries
If you want to do a two way ManyToMany both, you just only need to do this:
class Dealer(models.Model):
name = models.CharField(max_length=200)
contacts = models.ManyToManyField('Contact', blank=True)
class Contact(models.Model):
name = models.CharField(max_length=200)
dealers = models.ManyToManyField('Dealer', through=Dealer.projects.through, blank=True)
I guess it will work to you.
I have two models: Industry and Employer, as per below:
class Industry(models.Model):
name = models.CharField(max_length=255, unique=True)
class Employer(models.Model):
industry = models.ForeignKey(Industry)
name = models.CharField(max_length=255, unique=True)
The problem is that not all of the industries have employers yet... I want to get a list of all industries that have atleast one employer mapped to them, rather than getting them all. Is this possible with the ORM not with just regular SQL? I tried to find this in the django docs and coudlnt..
This is a classic problem for Django Annotations
Try:
from django.db.models import Count
Industry.objects.annotate(num_employers=Count('employer').filter(num_employers__gt=0)
I have an app with a similar structure as this snippet
class Blog(models.Model):
name = models.CharField(max_length=25)
class Category(models.Model):
name = models.CharField(max_length=25)
blog = models.ForeignKey(Blog)
class Entry(models.Model):
title = models.CharField(max_length=25)
category = models.ForeignKey(Category)
What is the most generic way, that i will be able to use in other apps to fetch all blogs with their category and entries?
I thought about creating a manager for the Blog model, that can fetch all the Categories for that blog, but it's hardcoding the model names
class BlogManager(models.Manager):
def categories(self):
return Category.objects.filter(blog=self)
Any suggestions?
What you want is a Select Related. It returns a QuerySet that will automatically "follow" foreign-key relationships, selecting that additional related-object data when it executes its query. Your query for Blogs would look something like:
Blog.objects.select_related().filter( something )
or
Blog.objects.select_related().get( something )
Why not use a standard way?
Filter using Blog's PK with FK relation.
Category.objects.filter(blog__pk=self.pk)
Django has a unique_for_date property you can set when adding a SlugField to your model. This causes the slug to be unique only for the Date of the field you specify:
class Example(models.Model):
title = models.CharField()
slug = models.SlugField(unique_for_date='publish')
publish = models.DateTimeField()
What would be the best way to achieve the same kind of functionality for a non-DateTime field like a ForeignKey? Ideally, I want to do something like this:
class Example(models.Model):
title = models.CharField()
slug = models.SlugField(unique_for='category')
category = models.ForeignKey(Category)
This way I could create the following urls:
/example/category-one/slug
/example/category-two/slug
/example/category-two/slug <--Rejected as duplicate
My ideas so far:
Add a unique index for the slug and categoryid to the table. This requires code outside of Django. And would the built-in admin handle this correctly when the insert/update fails?
Override the save for the model and add my own validation, throwing an error if a duplicate exists. I know this will work but it doesn't seem very DRY.
Create a new slug field inheriting from the base and add the unique_for functionality there. This seems like the best way but I looked through the core's unique_for_date code and it didn't seem very intuitive to extend it.
Any ideas, suggestions or opinions on the best way to do this?
What about unique_together?
class Example(models.Model):
title = models.CharField()
slug = models.SlugField(db_index=False)
category = models.ForeignKey(Category)
class Meta:
unique_together = (('slug','category'),)
# or also working since Django 1.0:
# unique_together = ('slug','category',)
This creates an index, but it is not outside of Django ;) Or did I miss the point?