django: Models with multiple Foreign Key queries - django

I have finished a proof-of-concept django project and now want to redesign the models to be more robust.
The basic model is called a PhraseRequest:
class PhraseRequest(models.Model):
user = models.ForeignKey(User)
timestamp = models.DateTimeField()
phrase = models.TextField()
Now the complication comes in that one PhraseRequest has a bunch of associated models, PhraseRequestVote, Phrase (a response), PhraseRequestComment&c.
Now when I list say, the top ten Phrase Requests in order of votes, my template has a for-each loop which is fed the ten PhraseRequest objects. It then populates the HTML with the request, and all it's associated data.
So far I have been adding to each PhraseRequest's dictionary to achieve this:
for r in phrase_requests:
r.votes = PhraseRequestVote.objects.filter(request=r)
r.n_votes = sum([v.weight for v in r.votes])
r.comments = PhraseRequestComment.objects.filter(request=r)
#and so on
Intuitively, this doesn't seem right - There must be a "correct" way to do this. Do I need to redesign the models? The query?

You can make function in your model and order it in your view. Like this
models.py
class model_name(models.Model)
........
def votes(self):
return Vote_Name.objects.filter(phrase_id=self).count()

Related

retrieve distinct values of manytomanyfield of another manytomanyfield

I have a simple question but multiple google searches left me without a nice solution. Currently I am doing the following:
allowed_categories = self.allowed_view.all().difference(self.not_allowed_view.all())
users = []
for cat in allowed_categories:
for member in cat.members.all():
users.append(member)
return users
I have a ManyToManyField to Objects that also have a ManyToManyField for instances of Users. In the code above, I am trying to get all the users from all those categories and get a list of all Users.
Later I would like the same in a method allowed_to_view(self, user_instance) but that's for later.
How would I achieve this using Django ORM without using nested for-loops?
[edit]
My models are as follows:
class RestrictedView(models.Model):
allowed_view = models.ManyToManyField(Category)
not_allowed_view = models.ManyToManyField(Category)
class Category(models.Model):
name = models.CharField(max_length=30)
members = models.ManyToManyField(User)
So, I've made the following one-liner with only one query towards the database. It took me some time...
users = User.objects.filter(pk__in=self.allowed_view.all().values("users").difference(self.not_allowed_view.all().values("users")))
This gives me a nice queryset with only the users that are in the allowed_view and explicitly not in the not_allowed_view.
Without seeing you database structure / models.py file its hard to say, but you can do a search on member objects like so:
members_queryset = Member.objects.filter(
category = <allowed categories>,
...
)
users += list(members.all())

Dynamic Django Model based on query

Hello folks Im new to Django(I have just the finished the tutorial) but I think i understand the basic concepts of it .Im writing here because Im trying to do something "difficult" for my current experience with django and searching the internet didnt give me a solution .What im trying to do is to create a dynamic model based on the number of entries of another model .To be more exact lets say i got the following model :
class criteria(models.Model):
criteria_text = models.CharField(max_length=200)
monotonicity = models.CharField(max_length=1,choices=(('+','ASCEDING'),('-','DESCENDING')),default='+',verbose_name='Monotonicity')
worst = models.IntegerField(default=0)
best = models.IntegerField(default=0)
What i want to do is create all the criteria models instances i want through the django admin panel and then query for all the creteria_text instances in the database and make a model with an attribute for every criteria_text instance.
So lets say I add the following criteria to the database(these are criteria_text attributes of criteria objects: Color,Weight,Price .
I want to end up with a model like this :
class Alternative(models.Model):
Color = models.IntegerField(default=0)
Weight = models.IntegerField(default=0)
Price = models.IntegerField(default=0)
The thing is that in my application this one has to happen a lot of times so i cannot make model each time someone adds an Alternative based on different criteria .
After searching i found that i can define dynamic models using the following format :
attrs = {
'name': models.CharField(max_length=32),
'__module__': 'myapp.models'
}
Animal = type("Animal", (models.Model,), attrs)
So the question is how can I define "attrs" based on a query that gets all the criteria in the database ?Can i define a relationship of this dynamic model with another model ? Also the models already created should be updated if a user adds more criteria .
Is something like this possible ?
If so please show me the path .
I don't think defining dynamic models is a good solution here (or anywhere, really). Rather, you need a relationship that can have as many items as there are criteria instances.
It might be something like this:
class Alternative(models.Model):
name = models.CharField(...)
choices = models.ManyToManyField("Criteria", through="AlternativeChoice")
class AlternativeChoice(models.Model):
alternative = models.ForeignKey('Alternative')
criteria = models.ForeignKey('Criteria')
value = models.IntegerField(default=0)
The real logic will belong in the form, where you will need to create options for each criteria entry, and validate the AlternativeChoice dependent on the related criteria.

related field nested lookup error

I have the following models:
class Profile(models.Model):
user = models.ForeignKey(User)# User can have more than one profile
class Order(models.Model):
ship_to = models.ForeignKey(Profile)
class Shipping(models.Model):
order = models.ForeignKey(Order)# one order can have more than one shipping
shipping_company = models.ForeignKey(Shipping_company)
class Shipping_company(models.Model):
name = ...
So now i have the following structure:
User > Receiver > Order > Shipping > Shipping_company
The question is: How can i get all User models, who ordered with specific Shipping company?
If i make a query like this
User.objects.filter(receiver__order__shipping__shipping_company__pk=1)
i get
FieldError: Relation fields do not support nested lookups
if i make something like this
sh_comp = items.objects.get(pk=1) # __unicode__ returns "FedEx"
User.objects.filter(receiver__order__shipping__shipping_company=sh_comp)
the result is
ValueError: Cannot query "FedEx": Must be "Receiver" instance.
This seemed to be a simple and trivial task, but i can't make it work.
One approach that can be taken is as following(I am only considering the four models you have presented in your question),
You have foreign key of Shipping company in Shipping model. So you can make use of model function here on Shipping_company model.
Take a look at this model function
class Shipping_company(models.Model):
fields...
def get_profiles(self):
shippings = Shipping.objects.filter(shipping_company=self)
users = list(set([x.order.ship_to for x in shippings]))
Explanation:
shippings = Shipping.objects.filter(shipping_company=self)
will return all the shippings for one Shipping company(FedEx in your case). Further loop through the shippings to get ship_to from order field.
PS: You can take it as reference and design your own solution.
Walkthrough:
Lets say there is shipping company 'FedEx'. So we do,
fedex = Shipping_company.objects.get(name='FedEx')
Now, when you call get_profiles on fedex, like
fedex.get_profiles()
what will happen is this.
fedex instance refers to self in get_profiles() function now.
Using self(fedex), we filter out shippings by fedex.
Then we loop through those shippings to get order per shipping and each of that order has a ship_to(profile) foreign key.
I guess, you are getting confused because of the return statement.
In elaborate fashion the whole function will look something like this
def get_profiles(self):
users = list()
shippings = Shipping.objects.filter(shipping_company=self)
for shipping in shippings:
order = shipping.order
#Now you have an order per shipping, so you do
if not order.ship_to in users:
users.append(order.ship_to)
return users

How can i get a list of objects from a postgresql view table to display

this is a model of the view table.
class QryDescChar(models.Model):
iid_id = models.IntegerField()
cid_id = models.IntegerField()
cs = models.CharField(max_length=10)
cid = models.IntegerField()
charname = models.CharField(max_length=50)
class Meta:
db_table = u'qry_desc_char'
this is the SQL i use to create the table
CREATE VIEW qry_desc_char as
SELECT
tbl_desc.iid_id,
tbl_desc.cid_id,
tbl_desc.cs,
tbl_char.cid,
tbl_char.charname
FROM tbl_desC,tbl_char
WHERE tbl_desc.cid_id = tbl_char.cid;
i dont know if i need a function in models or views or both. i want to get a list of objects from that database to display it. This might be easy but im new at Django and python so i having some problems
Django 1.1 brought in a new feature that you might find useful. You should be able to do something like:
class QryDescChar(models.Model):
iid_id = models.IntegerField()
cid_id = models.IntegerField()
cs = models.CharField(max_length=10)
cid = models.IntegerField()
charname = models.CharField(max_length=50)
class Meta:
db_table = u'qry_desc_char'
managed = False
The documentation for the managed Meta class option is here. A relevant quote:
If False, no database table creation
or deletion operations will be
performed for this model. This is
useful if the model represents an
existing table or a database view that
has been created by some other means.
This is the only difference when
managed is False. All other aspects of
model handling are exactly the same as
normal.
Once that is done, you should be able to use your model normally. To get a list of objects you'd do something like:
qry_desc_char_list = QryDescChar.objects.all()
To actually get the list into your template you might want to look at generic views, specifically the object_list view.
If your RDBMS lets you create writable views and the view you create has the exact structure than the table Django would create I guess that should work directly.
(This is an old question, but is an area that still trips people up and is still highly relevant to anyone using Django with a pre-existing, normalized schema.)
In your SELECT statement you will need to add a numeric "id" because Django expects one, even on an unmanaged model. You can use the row_number() window function to accomplish this if there isn't a guaranteed unique integer value on the row somewhere (and with views this is often the case).
In this case I'm using an ORDER BY clause with the window function, but you can do anything that's valid, and while you're at it you may as well use a clause that's useful to you in some way. Just make sure you do not try to use Django ORM dot references to relations because they look for the "id" column by default, and yours are fake.
Additionally I would consider renaming my output columns to something more meaningful if you're going to use it within an object. With those changes in place the query would look more like (of course, substitute your own terms for the "AS" clauses):
CREATE VIEW qry_desc_char as
SELECT
row_number() OVER (ORDER BY tbl_char.cid) AS id,
tbl_desc.iid_id AS iid_id,
tbl_desc.cid_id AS cid_id,
tbl_desc.cs AS a_better_name,
tbl_char.cid AS something_descriptive,
tbl_char.charname AS name
FROM tbl_desc,tbl_char
WHERE tbl_desc.cid_id = tbl_char.cid;
Once that is done, in Django your model could look like this:
class QryDescChar(models.Model):
iid_id = models.ForeignKey('WhateverIidIs', related_name='+',
db_column='iid_id', on_delete=models.DO_NOTHING)
cid_id = models.ForeignKey('WhateverCidIs', related_name='+',
db_column='cid_id', on_delete=models.DO_NOTHING)
a_better_name = models.CharField(max_length=10)
something_descriptive = models.IntegerField()
name = models.CharField(max_length=50)
class Meta:
managed = False
db_table = 'qry_desc_char'
You don't need the "_id" part on the end of the id column names, because you can declare the column name on the Django model with something more descriptive using the "db_column" argument as I did above (but here I only it to prevent Django from adding another "_id" to the end of cid_id and iid_id -- which added zero semantic value to your code). Also, note the "on_delete" argument. Django does its own thing when it comes to cascading deletes, and on an interesting data model you don't want this -- and when it comes to views you'll just get an error and an aborted transaction. Prior to Django 1.5 you have to patch it to make DO_NOTHING actually mean "do nothing" -- otherwise it will still try to (needlessly) query and collect all related objects before going through its delete cycle, and the query will fail, halting the entire operation.
Incidentally, I wrote an in-depth explanation of how to do this just the other day.
You are trying to fetch records from a view. This is not correct as a view does not map to a model, a table maps to a model.
You should use Django ORM to fetch QryDescChar objects. Please note that Django ORM will fetch them directly from the table. You can consult Django docs for extra() and select_related() methods which will allow you to fetch related data (data you want to get from the other table) in different ways.

django inner join query

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.