I've read the documentation and looked at other questions posted here, but I can't find or figure out whether this is possible in Django.
I have a model relating actors and movies:
class Role(models.Model):
title_id = models.CharField('Title ID', max_length=20, db_index=True)
name_id = models.CharField('Name ID', max_length=20, db_index=True)
role = models.CharField('Role', max_length=300, default='?')
This is a single table that has pairs of actors and movies, so given a movie (title_id), there's a row for each actor in that movie. Similarly, given an actor (name_id), there's a row for every movie that actor was in.
I need to execute a query to return the list of all title_id's that are related to a given title_id by a common actor. The SQL for this query looks like this:
SELECT DISTINCT r2.title_id
FROM role as r1, role as r2
WHERE r1.name_id = r2.name_id
AND r1.title_id != r2.title_id
AND r1.title_id = <given title_id>
Can something like this be expressed in a single Django ORM query, or am I forced to use two queries with some intervening code? (Or raw SQL?)
Normally I would break this into Actor and Movie table to make it easier to query, but your requirement is there so I will give it a go
def get_related_titles(title_id)
all_actors = Role.objects.filter(title_id=title_id).values_list('pk', flat=True)
return Role.objects.filter(pk__in=all_actors).exclude(title_id=title_id) # maybe u need .distinct() here
this should give you one query, validate it this way:
print(get_related_titles(some_title_id).query)
Related
I am new to using Many-Many fields and I really could not find a good example that explained on how to go on with this task.
I currently have two models modelJob and modelSkillSubscription now modelJob contains a Many-To-Maney fields of skills.
What I would like to do is
retrieve modelSkillSubscription if they contain any of the skills that I have obtained. Say modelJob contains [SkillA,SkillB,SkillC]. I would like to pass this to a filter and obtain all modelSkillSubscription that contains any of the skills from the List avoiding duplicates.
class modelJob(models.Model):
skills = models.ManyToManyField(modelSkill,blank=True)
class modelSkillSubscription(models.Model):
employer = models.ForeignKey(modelEmployer, on_delete=models.CASCADE, default=None, blank=True)
skills = models.ManyToManyField(modelSkill, blank=True)
Any suggestions on how I can accomplish this ?
You can filter the SkillSubscription models based on an existing Job instance (I'd drop the leading model, making the model name shorter and compliant with Python “CamelCase” class naming conventions):
job = Job.objects.get(id=1)
subscriptions = (SkillSubscription.objects
.filter(skills__in=job.skills.all())
.distinct()
)
This selects all subscriptions that have at least one skill in common with the job.
You can also wrap the job selection in the same query if you know the filter criteria:
subscriptions = (SkillSubscription.objects
.filter(skills__in=Job.objects.filter(
# your filter criteria
)
.values('skills'))
.distinct()
)
I thought about my problem for days and i need a fresh view on this.
I am building a small application for a client for his deliveries.
# models.py - Clients app
class ClientPR(models.Model):
title = models.CharField(max_length=5,
choices=TITLE_LIST,
default='mr')
last_name = models.CharField(max_length=65)
first_name = models.CharField(max_length=65, verbose_name='Prénom')
frequency = WeekdayField(default=[]) # Return a CommaSeparatedIntegerField from 0 for Monday to 6 for Sunday...
[...]
# models.py - Delivery app
class Truck(models.Model):
name = models.CharField(max_length=40, verbose_name='Nom')
description = models.CharField(max_length=250, blank=True)
color = models.CharField(max_length=10,
choices=COLORS,
default='green',
unique=True,
verbose_name='Couleur Associée')
class Order(models.Model):
delivery = models.ForeignKey(OrderDelivery, verbose_name='Delivery')
client = models.ForeignKey(ClientPR)
order = models.PositiveSmallIntegerField()
class OrderDelivery(models.Model):
date = models.DateField(default=d.today())
truck = models.ForeignKey(Truck, verbose_name='Camion', unique_for_date="date")
So i was trying to get a query and i got this one :
ClientPR.objects.today().filter(order__delivery__date=date.today())
.order_by('order__delivery__truck', 'order__order')
But, i does not do what i really want.
I want to have a list of Client obj (query sets) group by truck and order by today's delivery order !
The thing is, i want to have EVERY clients for the day even if they are not in the delivery list and with filter, that cannot be it.
I can make a query with OrderDelivery model but i will only get the clients for the delivery, not all of them for the day...
Maybe i will need to do it with a Q object ? or even raw SQL ?
Maybe i have built my models relationships the wrong way ? Or i need to lower what i want to do... Well, for now, i need your help to see the problem with new eyes !
Thanks for those who will take some time to help me.
After some tests, i decided to go with 2 querys for one table.
One from OrderDelivery Queryset for getting a list of clients regroup by Trucks and another one from ClientPR Queryset for all the clients without a delivery set for them.
I that way, no problem !
My data model consists of three main entities:
class User(models.Model):
...
class Source(models.Model):
user = models.ForeignKey(User, related_name='iuser')
country = models.ForeignKey(Country, on_delete=models.DO_NOTHING)
description = models.CharField(max_length=100)
class Destination(models.Model):
user = models.ForeignKey(User, related_name='wuser')
country = models.ForeignKey(Country)
I am trying to create a queryset which is join all sources with destinations by user (many to many). In such a way I would have a table with all possible source/destination combinations for every user.
In SQL I would simple JOIN the three tables and select the appropriate information from each table.
My question is how to perform the query? How to access the query data?
In django queries are done on the model object, its well documented. The queries or querysets are lazy and when they execute they generally return a list of dict, each dict in the list contains the field followed by the value eg: [{'user':'albert','country':'US and A :) ','description':'my description'},....].
All possible source,destination combinations for every user?
I think you will have to use a reverse relation ship to get this done eg:
my_joined_query = User.objects.values('user','source__country','source__description','destination__country')
notice that i'm using the smaller case name of the models Source and Destination which have ForeignKey relationship with User this will join all the three tabels go through the documentation its rich.
Edit:
To make an inner join you will have to tell the query, this can be simply achieved by using __isnull=False on the reverse model name:
my_innerjoined_query = User.objects.filter(source__isnull=False,destination__isnull=False)
This should do a inner join on all the tables.
Then you can select what you want to display by using values as earlier.
hope that helps. :)
I am trying to add an additional custom field to a django model. I have been having quite a hard time figuring out how to do the following, and I will be awarding a 150pt bounty for the first fully correct answer when it becomes available (after it is available -- see as a reference Improving Python/django view code).
I have the following model, with a custom def that returns a video count for each user --
class UserProfile(models.Model):
user = models.ForeignKey(User, unique=True)
positions = models.ManyToManyField('Position', through ='PositionTimestamp', blank=True)
def count(self):
from django.db import connection
cursor = connection.cursor()
cursor.execute(
"""SELECT (
SELECT COUNT(*)
FROM videos_video v
WHERE v.uploaded_by_id = p.id
OR EXISTS (
SELECT NULL
FROM videos_videocredit c
WHERE c.video_id = v.id
AND c.profile_id = p.id
)
) AS Total_credits
FROM userprofile_userprofile p
WHERE p.id = %d"""%(int(self.pk))
)
return int(cursor.fetchone()[0])
I want to be able to order by the count, i.e., UserProfile.objects.order_by('count'). Of course, I can't do that, which is why I'm asking this question.
Previously, I tried adding a custom model Manager, but the problem with that was I also need to be able to filter by various criteria of the UserProfile model: Specifically, I need to be able to do: UserProfile.objects.filter(positions=x).order_by('count'). In addition, I need to stay in the ORM (cannot have a raw sql output) and I do not want to put the filtering logic into the SQL, because there are various filters, and would require several statements.
How exactly would I do this? Thank you.
My reaction is that you're trying to take a bigger bite than you can chew. Break it into bite size pieces by giving yourself more primitives to work with.
You want to create these two pieces separately so you can call on them:
Does this user get credit for this video? return boolean
For how many videos does this user get credit? return int
Then use a combination of #property, model managers, querysets, and methods that make it easiest to express what you need.
For example you might attach the "credit" to the video model taking a user parameter, or the user model taking a video parameter, or a "credit" manager on users which adds a count of videos for which they have credit.
It's not trivial, but shouldn't be too tricky if you work for it.
"couldn't you use something like the "extra" queryset modifier?"
see the docs
I didn't put this in an answer at first because I wasn't sure it would actually work or if it was what you needed - it was more like a nudge in the (hopefully) right direction.
in the docs on that page there is an example
query
Blog.objects.extra(
select={
'entry_count': 'SELECT COUNT(*) FROM blog_entry WHERE blog_entry.blog_id = blog_blog.id'
},
)
resulting sql
SELECT blog_blog.*, (SELECT COUNT(*) FROM blog_entry WHERE blog_entry.blog_id = blog_blog.id) AS entry_count
FROM blog_blog;
Perhaps doing something like that and accessing the user id which you currently have as p.id as appname_userprofile.id
note:
Im just winging it so try to play around a bit.
perhaps use the shell to output the query as sql and see what you are getting.
models:
class Positions(models.Model):
x = models.IntegerField()
class Meta:
db_table = 'xtest_positions'
class UserProfile(models.Model):
user = models.ForeignKey(User, unique=True)
positions = models.ManyToManyField(Positions)
class Meta:
db_table = 'xtest_users'
class Video(models.Model):
usr = models.ForeignKey(UserProfile)
views = models.IntegerField()
class Meta:
db_table = 'xtest_video'
result:
test = UserProfile.objects.annotate(video_views=Sum('video__views')).order_by('video_views')
for t in test:
print t.video_views
doc: https://docs.djangoproject.com/en/dev/topics/db/aggregation/
This is either what you want, or I've completely misunderstood!.. Anywhoo... Hope it helps!
I am working with django and having a hard time grasping how to do complex queries
Here is my model
class TankJournal(models.Model):
user = models.ForeignKey(User)
tank = models.ForeignKey(TankProfile)
ts = models.DateTimeField(auto_now=True)
title = models.CharField(max_length=50)
body = models.TextField()
class Meta:
ordering = ('-ts',)
get_latest_by = 'ts'
I need to pull the username given the tank object.
The user object is the one built into django.. thanks!
EDIT:
I have tried this
print User.objects.filter(tankjournal__tank__exact=id)
It seems to not pull out just the id.. and pull out everything in tankjournal and match it to the tank object
If you already have your tank object you should be able to do:
tank.user.username
To reduce the database queries you might want to consider the use of select_related(), e.g.
tanks = TankJournal.objects.all().select_related()
for tank in tanks:
username = tank.user.username
if you have a specific tank id then:
tank = TankJournal.objects.select_related().get(id=123456)
username = tank.user.username
I may be misunderstanding your question, but a request on User.objects.filter() will return a list of User objects, not User ids. What you've written looks technically correct.
Remember, though, that the model you have sets up a one-to-many between the TankProfile object and the TankJournal. In other words, a single TankProfile can be associated with more than one TankJournal, and therefore to more than one user. Given this, you're query is doing the right thing, returning more than one User.