I have two tables 'Contact' and other is "Subscriber".. I want to Compare Contact_id of both and want to show only those Contact_id which is present in Contact but not in Subscriber.These two tables are in two different Models.
Something like this should work:
Contact.objects.exclude(
id__in=Subscriber.objects.all()
).values_list('id', flat=True)
Note that these are actually two SQL queries. I'm sure there are ways to optimize it, but this will usually work fine.
Also, the values_list has nothing to do with selecting the objects, it just modifies "format" of what is returned (list of IDs instead of queryset of objects - but same database records in both cases).
If you are excluding by some field other then Subscriber.id (e.g: Subscriber.quasy_id):
Contact.objects.exclude(
id__in=Subscriber.objects.all().values_list('quasy_id', flat=True)
).values_list('id', flat=True)
Edit:
This answer assumes you don't have a relationship between your Contact and Subscriber models. If you do, then see #navit's answer, it is a better choice.
Edit 2:
That flat=True inside exclude is actually not needed.
I assume you have your model like this:
class Subscriber(models.Model):
contact = models.ForeignKey(Contact)
You can do what you want like this:
my_list = Subscriber.objects.filter(contact=None)
This retrieves Subscribers which don't have a Contact. Retrieveing a list of Contacts is straightforward.
If you want to compare value of fields in two different tables(which have connection with ForeignKey) you can use something like this:
I assume model is like below:
class Contact(models.Model):
name = models.TextField()
family = models.TextField()
class Subscriber(models.Model):
subscriber_name = models.ForeignKey(Contact, on_delete=models.CASCADE)
subscriber_family = models.TextField()
this would be the query:
query = Subscriber.objects.filter(subscriber_name =F(Contact__name))
return query
Related
We have a limitation for order_by/distinct fields.
From the docs: "fields in order_by() must start with the fields in distinct(), in the same order"
Now here is the use case:
class Course(models.Model):
is_vip = models.BooleanField()
...
class CourseEvent(models.Model):
date = models.DateTimeField()
course = models.ForeignKey(Course)
The goal is to fetch the courses, ordered by nearest date but vip goes first.
The solution could look like this:
CourseEvent.objects.order_by('-course__is_vip', '-date',).distinct('course_id',).values_list('course')
But it causes an error since the limitation.
Yeah I understand why ordering is necessary when using distinct - we get the first row for each value of course_id so if we don't specify an order we would get some arbitrary row.
But what's the purpose of limiting order to the same field that we have distinct on?
If I change order_by to something like ('course_id', '-course__is_vip', 'date',) it would give me one row for course but the order of courses will have nothing in common with the goal.
Is there any way to bypass this limitation besides walking through the entire queryset and filtering it in a loop?
You can use a nested query using id__in. In the inner query you single out the distinct events and in the outer query you custom-order them:
CourseEvent.objects.filter(
id__in=CourseEvent.objects\
.order_by('course_id', '-date').distinct('course_id')
).order_by('-course__is_vip', '-date')
From the docs on distinct(*fields):
When you specify field names, you must provide an order_by() in the QuerySet, and the fields in order_by() must start with the fields in distinct(), in the same order.
Let's say we have a two models like these:
Artist(models.Model):
name = models.CharField(max_length=50)
Track(models.Model):
title = models.CharField(max_length=50)
artist = models.ForeignKey(Artist, related_name='tracks')
How can I filter this relationship to get the first foreign record?
So I've tried something like this, but it didn't work (as expected)
artists = Artist.objects.filter(tracks__first__title=<some-title>)
artists = Artist.objects.filter(tracks[0]__title=<some-title>)
Is there any way to make this work?
Here's a solution not taking performance into consideration.
Artist.objects.filter(tracks__in=[a.tracks.first() for a in Artist.objects.all()], tracks__title=<some_title>)
No list approach, as requested.
Artist.objects.filter(tracks__in=Track.objects.all().distinct('artist').order_by('artist', 'id'), tracks__title=<some_title>)
The order_by 'id' is important to make sure distinct gets the first track based on insertion. The order_by 'artist' is a requirement for sorting distinct queries. Read about it here: https://www.postgresql.org/docs/9.0/static/sql-select.html#SQL-DISTINCT
I have these two models that I would like to return the sum of. I get an database error about the subquery returning more than one row. What would be the best way to compare both without using a for statement?
AuthorizationT(models.Model)
ar_id = models.BigIntegerField(blank=True, null=True)
status_flag = models.BigIntegerField(blank=True, null=True)
BillT(models.Model)
paid_id = models.BigIntegerField(blank=True, null=True)
recvd = models.FloatField(blank=True, null=True)
Query I tried
paidbill= BillT.objects.values_list('paid_id', flat=true)
AuthorizationT.objects.values().filter(ar_id=paidbill, status_flag=0).aggregate(Sum('recvd'))
In SQL I know it would be
select sum(recvd) from authorization_t a, bill_t b where a.ar_billid0= b.paid_id and a.status_flag=0
I'm looking for the equivalent in queryset
I think you won't be able to achieve without a for loop because I think you need to join the tables as there is a filtration on both tables and you want to sum a field from the first table. The way to join tables would be prefetch_related() or select_related() but they utilize foreign keys.
This leads me to a suggestion that the id fields: bill_id and ar_id should be normalized as it looks like there will be data duplication. Using a relationship would also make making queries simpler.
Since paidbill is a list, you have to use the __in suffix in your query:
AuthorizationT.objects.filter(ar_id__in=paidbill,status_flag=0).aggregate(Sum('recvd'))
If you model the relation of the models (ar_id, paid_id) via a ForeignKey or ManyToMany, you will be able to do this trivially in a single ORM statement
class Post(models.Model):
created_time = models.DateTimeField()
comment_count = models.IntegerField(default=0)
like_count = models.IntegerField(default=0)
group = models.ForeignKey(Group)
class MonthPost(models.Model):
created_time = models.DateTimeField()
comment_count = models.IntegerField(default=0)
like_count = models.IntegerField(default=0)
group = models.ForeignKey(Group)
post = models.OneToOneField(Post)
I use this two models. MonthPost is part of Post.
I want to use MonthPost when filtered date is smaller than month.
_models = Model.extra(
select={'score': 'like_count + comment_count'},
order_by=('-score',)
)
I use extra about above two models. Post works well, but MonthPost doesn't work.
django.db.utils.ProgrammingError: column reference "like_count" is ambiguous
LINE 1: ... ("archive_post"."is_show" = false)) ORDER BY (like_count...
This is the error message.
_models.values_list("post", flat=True)
And then, I want to extract OneToOne field(post) from MonthPost.
I try to use values_list("post", flat=True). It return only id list.
I need to post object list for django rest framework.
I don't' quite understand what you are trying to achieve with your MonthPost model and why it duplicates Post fields. With that being said I think you can get the results you want with this info.
First of all extra is depreciated see the docs on extra. In either case, your select is not valid SQL syntax, your query should look more like this:
annotate(val=RawSQL(
"select col from sometable where othercol =%s",
(someparam,)))
However, what you are after here requires neither extra or RawSql. These methods should only be used when there is no built in way to achieve the desired results. When using RawSql or extra, you must tailor the SQL for your specific backed. Django has built in methods for such queries:
qs = Post.objects.all().annotate(
score=(Count('like_count') + Count('comment_count'))
A values_list() query needs to explicitly list all fields from related models and extra or annotated fields. For MonthPost it should look like this:
MonthPost.objects.all().values_list('post', 'post__score', 'post__created_time')
Finally, if the purpose of MonthPost is simply to list the posts with he greatest score for a given month, you can eliminate the MonthPost model entirely and query your Post model for this.
import datetime
today = datetime.date.today()
# Filter for posts this month
# Annotate the score
# Order the results by the score field
qs = Post.objects\
.filter(created_time__year=today.year, created_time__month=today.month)\
.annotate(score=(Count('like_count') + Count('comment_count'))\
.order_by('score')
# Slice the top ten posts for the month
qs = qs[:10]
The code above is not tested, but should give you a better handle on how to perform these types of queries.
I have tables called 'has_location' and 'locations'. 'has_location' has user_has and location_id and its own id which is given by django itself.
'locations' have more columns.
Now I want to get all locations of some certain user. What I did is..(user.id is known):
users_locations_id = has_location.objects.filter(user_has__exact=user.id)
locations = Location.objects.filter(id__in=users_locations_id)
print len(locations)
but I am getting 0 by this print. I have data in db. but I have the feeling that __in does not accept the models id, does it ?
thanks
Using __in for this kind of query is a common anti-pattern in Django: it's tempting because of its simplicity, but it scales poorly in most databases. See slides 66ff in this presentation by Christophe Pettus.
You have a many-to-many relationship between users and locations, represented by the has_location table. You would normally describe this to Django using a ManyToManyField with a through table, something like this:
class Location(models.Model):
# ...
class User(models.Model):
locations = models.ManyToManyField(Location, through = 'LocationUser')
# ...
class LocationUser(models.Model):
location = models.ForeignKey(Location)
user = models.ForeignKey(User)
class Meta:
db_table = 'has_location'
Then you can fetch the locations for a user like this:
user.locations.all()
You can query the locations in your filter operations:
User.objects.filter(locations__name = 'Barcelona')
And you can request that users' related locations be fetched efficiently using the prefetch_related() method on a query set.
You are using has_location's own id to filter locations. You have to use location_ids to filter locations:
user_haslocations = has_location.objects.filter(user_has=user)
locations = Location.objects.filter(id__in=user_haslocations.values('location_id'))
You can also filter the locations directly through the reverse relation:
location = Location.objects.filter(has_location__user_has=user.id)
What do your models look like?
For your doubt, __in does accept filtered ids.
For your current code, the solution:
locations = Location.objects.filter(id__in=has_location.objects.filter(user=user).values('location_id'))
# if you just want the length of the locations, evaluate locations.count()
locations.count()
# if you want to iterate locations to access items afterwards
len(locations)