I have such model
Post (models.Model):
recommended = models.BooleanField (default=False)
when I get all objects from model I have
posts = Post.objects.all()
posts.count() # show equals to 18
posts[0].recommended # equals to False
but when I try to filter it by recommended tag I get total count equals to 0 even in model they all have the same value as I request in filter
posts = Post.objects.filter(recommended=False)
posts.count() # show equals to 0
Looks like there was not any values in this field because there vas crated before I make this field in model
If you want to fetch objects that have either False or NULL value you can do it like this:
Post.objects.exclude(recommended=True)
Although I'd rather suggest to fix your database by issuing an UPDATE query that will change all NULL values to False (do it from django shell):
Post.objects.filter(recommended__isnull=True).update(recommended=False)
It would be also good to alter your table to include NOT NULL in column definition.
Related
Two models Users (built-in) and Posts:
class Post(models.Model):
post_date = models.DateTimeField(default=timezone.now)
user = models.ForeignKey(User, on_delete=models.CASCADE, null=True, related_name='user_post')
post = models.CharField(max_length=100)
I want to have an API endpoint that returns the percentage of users that have posted. Basically I want SUM(unique users who have posted) / total_users
I have been trying to play around with annotate and aggregate, but I am getting the sum of posts for each users, or the sum of users per post (which is one...). How can I get the sum of posts returned with unique users, divide that by user.count and return?
I feel like I am missing something silly but my brain has gone to mush staring at this.
class PostParticipationAPIView(generics.ListAPIView):
queryset = Post.objects.all()
serializer_class = PostSerializer
def get_queryset(self):
start_date = self.request.query_params.get('start_date')
end_date = self.request.query_params.get('end_date')
# How can I take something like this, divide it by User.objects.all().count() * 100, and assign it to something to return as the queryset?
queryset = Post.objects.filter(post_date__gte=start_date, post_date__lte=end_date).distinct('user').count()
return queryset
My goal is to end up with the endpoint like:
{
total_participation: 97.3
}
Thanks for any guidance.
BCBB
EDIT
OK, I am still struggling a bit. I tried to create a serializer that just had a decimal field for participation_percentage like:
percentage_participation = serializers.DecimalField(max_digits=5, decimal_places=2, max_value=100, min_value=0)
Then I calculate in the view, but I get an error:
Got AttributeError when attempting to get a value for field percentage_participation on serializer ParticipationSerializer.
The serializer field might be named incorrectly and not match any attribute or key on the str instance.
Original exception text was: 'str' object has no attribute 'percentage_participation'.
Error was the same if I made it a CharField (in case there was some string coercion?).
So then I tried to move it to a Serializer Method and put all the calculation logic in there. This calculated fine, but if I had to provide a query_set in the view. If provided a model object, it just returned the percentage as many times as the query (say Posts.objects.all() had a total of 100 posts, it returned the percentage 100 times).
So then I tried to override the get_queryset in the view, but I HAVE to return something. If I just return { "meh", "hello" } then I return the percentage from the SerializerMethodField one time and the end result is exactly what I want.
I just have no idea as to WHY or how to do this correctly.
Thanks for your help.
EDIT #2
OK so I realized why I was only getting one, it was iterating over the string I returned, which was one character. When I returned "meh" it gave me three of the percentage, iterating over each character in the string...
I am not understanding from playing around, reading the docs, or using GoogleFu how to do this properly. I just want to be able to perform some kind of summary logic on records from the DB - how can I do this properly?!?!
Thank you for all your time.
BCBB
something like this should work
# get total user count
total_users = User.objects.count()
# get unique set of users with post
total_users_who_posted = Post.objects.filter(...).distinct("user").count()
# calculate_percentage
percentage = {
"total_participation": (total_users_who_posted*100)/ total_users
}
# take caution of divion by zero
I don't think it is possible to use djangos orm to do this completely but you can use the orm to get the user counts (with posts and total):
from django.db.models import BooleanField, Case, Count, When, Value
counts = (User
.objects
.annotate(posted=Case(When(user_post__isnull=False,
then=Value(True)),
default=Value(False),
output_field=BooleanField()))
.values('posted')
.aggregate(posted_users=Count('pk', filter=Q(posted=True)),
total_users=Count('pk', filter=Q(posted__isnull=False)))
# This will result in a dict containing the following:
# counts = {'posted_users': ...,
# 'total_users': ....}
Currently I am filtering empty fields in all entries of the queryset like this:
data_qs = DataValue.objects.filter(study_id=study.id) #queryset
opts = DataValue._meta # get meta info from DataValue model
field_names = list([field.name for field in opts.fields]) # DataValue fields in a list
field_not_empty = list() # list of empty fields
for field in field_names:
for entry in data_qs.values(field):
if entry.get(field) is not None:
field_not_empty.append(field)
break
It works but not sure if it is an appropriate solution....
Does anyone know how to filter empty values in all the queryset? The table have more than 30 fields, so depending on the study ID some querysets may contain the field1 all empty, other study ID may contain all the field2 empty.
Does the Django ORM provide an easy an clean solution to do this?
Thanks in advance
To check if some value in a QuerySet is empty, say the values name is "title".
This will exclude all empty fields
DataValue.objects.filter(study_id=study.id).exclude(title__exact='')
If you only want the empty fields, just filter it
DataValue.objects.filter(study_id=study.id, title__exact='')
Hope it helped.
I have the following model in django:
class task(models.Model):
admin = models.BooleanField()
date = modesl.DateField()
I am trying to achieve a filter which provides me with a query_set that prioritize if admin = True
So assume I have these 3 rows :
admin = True , date = 01-01-2019
admin = False , date = 01-01-2019
admin = False , date = 02-02-2019
The output of the query set will be :
admin = True , date = 01-01-2019
admin = False , date = 02-02-2019
it should filter out the row with 01-01-2019 which admin=False because there is already an admin=True row which should take prioritization.
I could do it by fetching all and removing it from the query_set myself, but want to make sure there is no other way of doing it before.
Rather than looping through the QuerySet and removing them yourself, one thing you could do is:
Fetch all the dates where admin is True
Fetch all the objects where either:
i. admin is True
ii. The date is not in part 1 (e.g. admin is False)
This can be achieved with the following:
from django.db.models import Q
true_dates = task.objects.filter(admin=True).values_list("date", flat=True)
results = task.objects.filter(Q(admin=True)|~Q(date__in=true_dates))
This will most likely be more efficient than looping through your results yourself.
Note that since querysets are 'lazy' (this means only evaluated when they absolutely have to be) this will result in just 1 db hit
Tim's answer is close, but incomplete, because he doesn't use Subquery().
This answer provides the same results, without having an additional query hit the database:
from django.db.models import Subquery, Q
dates = Task.objects.filter(admin=True)
tasks = Task.objects.filter(Q(admin=True) | ~Q(date__in=Subquery(dates.values('date')))
My question is simple: in a Django app, I have a table Users and a table StatusUpdates. In the StatusUpdates table, I have a column user which is a foreign key pointing back to Users. How can I do a search expressing something like:
users.filter(latest_status_update.text__contains='Hello')
Edit:
Please excuse my lack of clarity. The query that I would like to make is something like "Give me all the users whose latest status update contains the text 'hello'". In Django code, I would do the following (which is really inefficient and ugly):
hello_users = []
for user in User.objects.all():
latest_status_update = StatusUpdate.objects.filter(user=user).order_by('-creation_date')[0]
if latest_status_update.text.contains('Hello'):
hello_users.append(user)
return hello_users
Edit 2:
I've already found the solution but since I was asked, here are the important parts of my models:
class User(models.Model):
...
class StatusUpdate(models.Model):
user = models.ForeignKey(User)
text = models.CharField(max_length=140)
creation_date = models.DateTimeField(auto_now_add=True, editable=False)
....
Okay, I think I got it:
from django.db.models import Max, F
User.objects\
.annotate(latest_status_update_id=Max('statusupdate__id'))\
.filter(
statusupdate__id=F('latest_status_update_id'),
statusupdate__text__icontains='hello'
)
For more info, see this section of the Django documentation.
Please note: I ended up changing my strategy a bit and settling for the strategy where the highest ID means the latest update. This is the case because I realized that a User could post two updates the same time and that would break my query.
latest_status_updates = filter(lambda x: x.text.contains('hello'),
[
user.statusupdates_set.order_by('-creation_date').first()
for user in User.objects.all()
]
)
users = list(set([status_update.user for status_update in latest_status_updates]))
EDIT:
Now I first get all LATEST status updates of each user into a list which is then filtered by the text field found in StatusUpdate class. In the second line, I extract users out of the filtered status updates and then produce a unique list of users.
I hope this helps!
Not sure I understand, are you trying to do something like
(StatusUpdates
.objects
.select_related("user")
.filter(text__contains = "hello")
.order_by("-updated")
.first())
This will return the StatusUpdate that was modified last (if you have a field called updated that stores the time of the last modification) which contains "Hello" in the text field. If none of the StatusUpdates contains that string, it will return None.
Then you can do:
latest = (StatusUpdates
.objects
.select_related("user")
.filter(text__contains = "hello")
.order_by("-updated")
.first())
#then if you needed the user too
if latest is not None:
user = latest.user #which does not call the DB again since you selected related`
If this isn't what you needed, please provide more details (models) and clarify your need
So here's a field I have in one of my models:
year = models.ForeignKey(Year, blank=True, null=True)
Now I want to get all the objects of that model whose year field is either null or specific_year.
This is what I tried:
MyModel.objects.filter(year__isnull=True, year=specific_year)
MyModel.objects.filter(year__isnull=True).filter(year=specific_year)
MyModel.objects.filter(year__in=[specific_year, None])
but they all give me an empty result.
I am pretty new to Django, so maybe there is something I'm missing here, but I couldn't find an answer in the docs. So how can I filter for all the objects whose year field is either null or specific_year?
You can use Q objects for complex filtering
from django.db.models import Q
MyModel.objects.filter(Q(year__isnull=True) | Q(year=specific_year))
By default, using , or nested filtering would yield an AND result, whereas you need an OR result, for which you can use Q