Develop Reference

Django: How do you compare a QuerySet with fields on a ForeignKey object's property?

I am trying to query a model against a field on a ForeignKey object's property.
I have the following models:
class Song(models.Model):
name = models.CharField(max_length=20)
limit = models.IntegerField()
class Recording(models.Model):
song = models.ForeignKey(Song, on_delete=models.CASCADE)
status = models.CharField(
max_length=1,
choices=STATUS_CHOICES,
default=OPEN
)
I would like to query Songs that have Recordings with status OPEN with a count of more than 'limit' (the field on Song). Looking over the django aggregation docs I tried something along the lines of:
# View
get(self):
songs_count = Count('recording', filter=Q(recording__status='O'))
songs = Song.objects.annotate(songs_count=songs_count)
results = songs.filter(songs_count__gt=< each song.limit... >)
Can someone point the way on how to build this query?
I greatly appreciate any and all feedback.

You can work with an F object [Django-doc] to refer to a field, so:
from django.db.models import F, Q
Songs.objects.annotate(
songs_count=Count('recording', filter=Q(recording__status='O'))
).filter(songs_count__gt=F('limit'))

'ReverseManyToOneDescriptor' object has no attribute 'filter' Django

Hi there Im trying to retrieve a specific object from the related model so as to render data to my view specific to that particular object, in my case I have a custom user model and a related model called Seller.
Models
from django.db import models
from django.contrib.auth.models import AbstractUser
# Create your models here.
class CustomUser(AbstractUser):
is_customer = models.BooleanField(default=False)
is_seller = models.BooleanField(default=False)
class Seller(models.Model):
user = models.ForeignKey(CustomUser, on_delete=models.CASCADE, blank=True, null=True)
store_name = models.CharField(max_length=120)
address = models.CharField(max_length=180)
phone = models.IntegerField(blank=True, null=True)
email = models.CharField( max_length=180, blank=True, null=True )
def __str__(self):
return self.store_name
View
#method_decorator( seller_required , name='dispatch')
class SellerDashBoardView(ListView):
model = Seller
template_name = 'seller_dashboard.html'
def get_context_data(self, *args, **kwargs):
user = CustomUser.seller_set.filter(store_name=self.request.user.username)
context = super(SellerDashBoardView, self).get_context_data( **kwargs)
context['products'] = Product.objects.filter(seller=user)[:6]
return context

This is because when you want to filter ManyToOne reverse Relation, you have to make exact the same query as you would've been done with a direct relation:
CustomUser.objects.filter(seller__store_name="Whole Foods")
# Note that would return a queryset not a single user!
# If you want a CustomUser object you will have to use either get or index the query
The doc example and explanations are provided here:
https://docs.djangoproject.com/en/3.1/topics/db/examples/many_to_one/
It is also better to use prefetch_related method to tell djano ORM that it does not have to make as many queries as number of related objects, that query should be done in 2 database queries instead of lenght of your related query:
CustomUser.objects.prefetch_related("seller_set").filter(seller__store_name="Whole Foods")
The doc link:
https://docs.djangoproject.com/en/3.1/ref/models/querysets/#prefetch-related
You probably would like to use ...seller_set.filter when you already got a CustomUser object. So if you want to filter its sellers you would use that:
...
user.seller_set.filter(store_name="Whole Foods")
That would provide you the Seller objects queryset filtered by a store name related to a specific user. Basically the same query as this:
Seller.objects.filter(user_pk=user.pk, store_name="Whole Foods")

Cannot resolve keyword 'last_activity' into field

As title says I was trying to sort a list of posts using the django order_by method and since the field I used was later added to the list (The field was not created inside the model) it failed.
Is there anything I can do about it other than adding the field to the model which is something I really don't wanna do?
Here is the model code
class post(models.Model):
title = models.CharField(max_length=236)
content = models.TextField()
post_board = models.ForeignKey(board, on_delete=models.CASCADE)
author = models.ForeignKey(User, on_delete=models.CASCADE)
release_date = models.DateField(auto_now_add=True)
views = models.IntegerField(default=0)
def __str__(self):
return self.title
The function that adds the extra field:
def forumdisplay(request, boardslug=None):
context = { 'board': None }
if boardslug:
context['board'] = board.objects.all().filter(slug=boardslug).first()
if context['board']:
context['posts'] = post.objects.all().filter(post_board=context['board'])
for eachpost in context['posts']:
eachpost.reply_count = len(reply.objects.all().filter(reply_to=eachpost))
eachpost.last_activity = eachpost.release_date
if eachpost.reply_count:
eachpost.last_activity = reply.objects.all().filter(reply_to=eachpost).order_by('release_date').first().release_date
context['posts'] = context['posts'].order_by('last_activity')
alter_posts(context['posts'])
else:
pass
return render(request, "board/forumdisplay.html", context)
The error I got:
Request Method: GET
Request URL: http://127.0.0.1:8000/forumdisplay/news/
Django Version: 3.0.4
Exception Type: FieldError
Exception Value:
Cannot resolve keyword 'last_activity' into field. Choices are: author, author_id, content, id, post_board, post_board_id, release_date, reply, title, views```

You can't.
order_by that you are trying to use is actually will be translated into SQL command to be executed on database, and while database has no column called last_activity so you can't apply this function to it.
what is the problem to add a new column to your DB and make it nullable?

Django no such column ForeignKey

I'm doing a Django project (kind of social network) and want to have a page where I can see all my posts, which I did.
I allways get the error: no such column: uploaded_by
in models.py
from django.db import models
from django.contrib.auth.models import User
class ContentItem(models.Model):
upload_date = models.DateTimeField(auto_now=True)
title = models.CharField(max_length=100, default='no title')
description = models.CharField(max_length=400, default='no description')
image = models.ImageField(upload_to='image_board/posts/', default='null')
uploaded_by = models.ForeignKey(User, default='0')
def __str__(self):
return self.title
in views.py
def view_my_favorites(request):
all_posts = ContentItem.objects.raw('SELECT * FROM image_board_ContentItem WHERE uploaded_by = request.user.username')
template = loader.get_template('favorites.html')
context = {
'all_posts': all_posts,
}
return HttpResponse(template.render(context, request))
I want to get the user name of the user who is loged in, how can i whrite this in the sql query?
Thaks guys :)

Your actual issue is probably caused by neglecting to make and run migrations after adding the uploaded_by field.
But there are a huge number of other things wrong here.
Firstly, you are comparing the uploaded_by column with a non-existent column, request.user.username. You need to use the actual value of that variable.
Secondly, you are comparing a foreign key - uploaded_by - with a string, username. These will never match.
Thirdly, you are using a raw query. There is absolutely no need to do that here.
Your query is trivial to express in the Django query syntax. You should do:
all_posts = ContentItem.filter(uploaded_by=request.user)
or even simpler:
all_posts = request.user.contentitem_set.all()

Django ordering in admin [duplicate]

I'm trying to sort a Django Admin list page by a specific value in the objects' related foreign key set.
Specifically, in the below code, I want the ContentAdmin view to show a list of all content objects sorted by the "Twitter Score" (The Score object with name "Twitter").
In the django app I have the following models:
class Content(models.Model):
body = models.CharField(max_length=564)
title = models.CharField(max_length=64)
class Score(models.Model):
name = models.CharField(max_length=64)
score = models.IntegerField()
content = models.ForeignKey('Content')
And in the admin.py I have the following:
class ContentAdmin(admin.ModelAdmin):
list_display = ('title', 'show_twitter_score',)
def show_twitter_score(self, obj):
twitter_score = obj.score_set.get(name='Twitter')
return 'Twitter: ' + str(twitter_score.score)
GOAL: The admin panel for ContentAdmin displays the content objects ordered by "Twitter" scores
Thanks everyone!

I solved this by extending the get_queryset method of the ContentAdmin class. After that, it was just a matter of getting the right ORM query
def get_queryset(self, request):
qs = super(ContentAdmin, self).get_queryset(request)
return qs.filter(score__name='Twitter').order_by('-score__score')
For Django 1.5 and earlier, the method was queryset.
def queryset(self, request):
qs = super(ContentAdmin, self).queryset(request)
return qs.filter(score__name='Twitter').order_by('-score__score')

If I understand correctly, you can try this from ModelAdmin.list_display in Django's documentation:
Usually, elements of list_display that aren't actual database fields can't be used in sorting (because Django does all the sorting at the database level).
However, if an element of list_display represents a certain database field, you can indicate this fact by setting the admin_order_field attribute of the item.
For example:
class Person(models.Model):
first_name = models.CharField(max_length=50)
color_code = models.CharField(max_length=6)
def colored_first_name(self):
return '<span style="color: #%s;">%s</span>' % (self.color_code, self.first_name)
colored_first_name.allow_tags = True
colored_first_name.admin_order_field = 'first_name'
class PersonAdmin(admin.ModelAdmin):
list_display = ('first_name', 'colored_first_name')
The above will tell Django to order by the first_name field when trying to sort by colored_first_name in the admin.
You can try this workaround in your code for the sorting.

Since django admin uses the db to sort you cant sort on the function you are showing in the list.
What you can do is to add the column you want to show to the queryset that django admin is using to list your models, this way you can have sorting.
To add the column you need you have to use the queryset extra method.
This should do the trick :)
Content.objects.all().extra(select={'twitter_score': 'SELECT score from content_score WHERE content_score.id = content_content.id'})
BONUS ROUND:
Content.objects.all().extra(select={'twitter_score': 'SELECT 'Twitter score:' || score from content_score WHERE content_score.id = content_content.id'})