These are my models
class Order(models.Model):
name = ...
class OrderDetail(models.Model)
order = models.OneToOneField(Order,null=False)
comment = ...
class LastUpdate(models.Model)
order = models.OneToOneField(Order,null=False)
date = ...
When I write Order.objects.all().values() it gives me a list which only contains name
But I need to get the name,orderdetail__comment,lastupdate__date values.
I can get them by writing
Order.objects.values('name','orderdetail__comment','lastupdate__date').all()
but there are a lot of related models to the order and I don't want to write all of them.
How can I get the all values of the related fields?
First, you query by
orders = Order.objects.select_related('orderdetail__comment', 'lastupdate__date')
then, get values by
orders.values('name', 'orderdetail__comment', 'lastupdate__date')
Related
I have the following model in django
class params(models.Model):
name = models.CharField(max_length=30, default = 'no_name')
cs_n = models.IntegerField(default=16)
alt_n = models.IntegerField(default=2)
opt_out = models.BooleanField(default=1)
at_n = models.IntegerField(default=4)
I want to create a new model with as many fields as at_n. For example, if the user enter "4" in at_n, I want this to create automatically:
class params(models.Model):
at_1 = models.IntegerField(default=2)
at_2 = models.IntegerField(default=2)
at_3 = models.IntegerField(default=2)
at_4 = models.IntegerField(default=2)
Thanks
This probably isn't a good data model to follow as Django models are intended to closely mirror database tables. For example, you wouldn't want to dynamically update the DDL of a table in a database because doing so places you at risk of messing up data that already exists in said table.
Instead, I think it would be a better approach for you to re-evaluate your data model.
For example, if there was a main object you were trying to tie these attributes to, then make a model for that main object and then make a separate model for main object attributes/values.
From there, you could use view logic to actually validate that the appropriate number of attributes assigned to a particular main object.
I'm thinking something kind of like this:
class MainModel(models.Model):
....
{Your main model attributes}
at_n = models.IntegerField(default=4)
....
class MainModelAttributes(model.Model):
main_model = models.ForeignKey(MainModel)
attr_value = models.IntegerField()
Then in your views.py file, you could use logic to make sure that the number of attributes on the MainModelAttributes model match the number stored in MainModel.at_n.
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())
Let's say we have the following models:
class Author(Model):
...
class Serie(Model):
...
class Book(Model):
authors = ManyToManyField(Author, related_name="books")
serie = ForeignKey(Serie)
...
How can I get the list of authors, with their series ?
I tried different combinations of annotate and prefetch:
list_authors = Author.objects.prefetch(Prefetch("books__series", queryset=Serie.objects.all(), to_attr="series"))
Trying to use list_authors[0].series throws an exception because Author has no series field
list_authors = Author.objects.annotate(series=FilteredExpression("books__series", condition=Q(...))
Trying to use list_authors[0].series throws an exception because Author has no series field
list_authors = Author.objects.annotate(series=F('books__series'))
returns all possible combinations of (author, serie) that have a book in common
As I'm using PostgreSQL for my database, I tried:
from django.contrib.postgres.aggregates import ArrayAgg
...
list_authors = Author.objects.annotate(series=ArrayAgg('books__serie', distinct=True, filter=Q(...)))
It works fine, but returns only the id of the related objects.
list_authors = Author.objects.annotate(series=ArrayAgg(
Subquery(
Serie.objects.filter(
livres__auteurs=OuterRef('pk'),
...
).prefetch_related(...)
)
))
fails because it needs an output_field, and a Model is not a valid value for output_field
BUT
I can get the number of series for an author, so why not the actual list of them:
list_authors = Author.objects.annotate(nb_series=Count("books__series", filter=Q(...), distinct=True)
list_authors[0].nb_series
>>> 2
Thus I assume that what I try to do is possible, but I am at a loss regarding the "How"...
I don't think you can do this with an annotation on the Author queryset - as you've already found you can do F('books__series') but that will not return distinct results. Annotations generally only make sense if the result is a single value per row.
What you could do instead is have a method on the Author model that fetches all the series for that author with a relatively simple query. This will mean one additional query per author, but I can't see any alternative. Something like this:
class Author:
def get_series(self):
return Serie.objects.filter(book__authors=self).distinct()
Then you just do:
list_authors = Author.objects.all()
list_authors[0].get_series()
I have models:
class Z(models.Model):
name = ...
class B(model.Model):
something = model...
other = models.ForeignKey(Z)
class A(models.Model):
date = model.DateTimeField()
objs_b = models.ManyToManyField(B)
def get_obj_b(self,z_id):
self.obj_b = self.objs_b.get(other=z_id)
and query:
qs = A.objects.filter(...)
but if I want get object B related to A I must call get_obj_b:
for item in gs:
item.get_obj_b(my_known_z_id)
It was generate many queries. How to do it simple? I can not change models, and generally I must use filter (not my own manager) function.
If you are using Django 1.4, I would suggest that you use prefetch_related like this:
A.objects.all().prefetch_related('objs_b__other')
This would minimize the number of queries to 2: one for model A, and one for 'objs_b' joined with 'other'
And you can combine it with a filter suggested by pastylegs:
A.objects.filter(objs_b__other__id=z_id).prefetch_related('objs_b__other')
For details see: https://docs.djangoproject.com/en/1.4/ref/models/querysets/#prefetch-related
I have models as follows:
class Place(models.Model):
name = models.CharField(max_length=300)
class Person(models.Model):
name = models.CharField(max_length=300)
class Manor(models.Model):
place = models.ManyToManyField(Place, related_name="place"))
lord = models.ManyToManyField(Person, related_name="lord")
overlord = models.ManyToManyField(Person, related_name="overlord")
I want to get all the Places attached with the relation 'lord' to a particular person, and then get the centre, using a GeoDjango method. This is as far as I've got:
person = get_object_or_404(Person, namesidx=namesidx)
manors = Manor.objects.filter(lord=person)
places = []
for manor in manors:
place_queryset = manor.place.all()
for place in place_queryset:
places.append(place)
if places.collect():
centre = places.collect().centroid
However, this gives me:
AttributeError at /name/208460/gamal-of-shottle/
'list' object has no attribute 'collect'
Can I either (a) do this in a more elegant way to get a QuerySet of places back directly, or (b) construct a QuerySet rather than a list in my view?
Thanks for your help!
The way you're doing this, places is a standard list, not a QuerySet, and collect is a method that only exists on GeoDjango QuerySets.
You should be able to do the whole query in one go by following the relations with the double-underscore syntax:
places = Place.objects.filter(manor__lord=person)
Note that your use of related_name="place" on the Manor.place field is very confusing - this is what sets the reverse attribute from Place back to Manor, so it should be called manors.