I have following models:
class EnMovielist(models.Model):
content_ID = models.CharField(max_length=30)
release_date = models.CharField(max_length=30)
running_time = models.CharField(max_length=10)
actress = models.CharField(max_length=300)
series = models.CharField(max_length=30)
studio = models.CharField(max_length=30, null=True)
director = models.CharField(max_length=30)
def __str__(self):
return self.content_ID
class EnActress(models.Model):
name = models.CharField(max_length=100, null=True)
movielist = models.ManyToManyField(EnMovielist, related_name='movies')
def __str__(self):
return self.name
I got error when I try to this in Django shell,
b = EnActress.objects.values_list('name', flat=True)
a = EnMovielist.objects.filter(actress__contains=b).values_list('content_ID')
b.movielist.add(a)
AttributeError: 'QuerySet' object has no attribute 'movielist'
How can I django queryset add into many-to-many field?
I have no idea why this is happening.. Any help appreciated! :)
You should not be using values_list if you intend to add a new relation afterwards. From the docs:
values() and values_list() are both intended as optimizations for
a specific use case: retrieving a subset of data without the
overhead of creating a model instance
[Emphasis mine]
It's hard to tell what you're up to without having a good description of what you want to achieve.
You should call m2m add from instance and adding entity should be also model instance. Otherwise your expression doesn't make sense.
b = EnActress.objects.get(pk=some_pk) # get an instance, not queryset
a = EnMovielist.objects.get(pk=some_pk) # also instance
b.movielist.add(a)
Related
class Patient(models.Model):
user = models.OneToOneField(User, related_name='patient', on_delete=models.CASCADE)
id_type = models.CharField(max_length=300)
id_number = models.CharField(max_length=300)
creation_date = models.DateField(default=datetime.date.today)
class Allergie(models.Model):
name = models.CharField(max_length=300, default="X")
class PatientAllergies(models.Model):
patient = models.ForeignKey(Patient, related_name="patient_allergies", on_delete=models.CASCADE)
allergie = models.ForeignKey(Allergie, on_delete=models.CASCADE, null=True)
professional_contract = models.ForeignKey(ProfessionalContract, null=True ,on_delete=models.CASCADE)
Is it possible to retrieve a patient objecto with a property that is a list of all his allergies, including name and id with these models?
you have the PatientAllergies as a chain,
so
patientAllergies = PatientAllergies.objects.get(patient.id_number='0000')
patientAllergies.allergie #you get the single allergie model connect with it, take care it is a foreignKey so it is singolar and not many
patientAlleriges.patient.user #will give you access to all the data of the user
You can achieve this with prefetch_related and Prefetch like so:
Patient.objects.prefetch_related(
Prefetch('patient_allergies__allergie', to_attr='allergies')
)
EDIT: Just learned that to_attr will not work on multiple levels of prefetch. Another approach I can think of is use a model property for Patient that returns its related allergies like this:
class Patient(models.Model):
#property
def allergies(self):
return Allergie.objects.filter(patientallergies_set__patient=self)
Then in your serializer, the allergies field can use the Allergies serializer
I have models as shown below,
class Manufacturer(models.Model):
name = models.CharField(max_length=100)
class Car(models.Model):
manufacturer = models.ForeignKey(Manufacturer, on_delete=models.CASCADE)
name = models.CharField(max_length=300)
#property
def latest_variant(self):
return self.carvariant_set.last()
class CarVariant(models.Model):
car = models.ForeignKey(Car, on_delete=models.CASCADE)
name = models.CharField(max_length=300)
and I am making a query to get the latest variant of all cars, I am getting much duplicated queries.
I couldn't eliminate it with prefetch_related
Car.objects.all().prefetch_related('carvariant_set')
How can I eliminate the duplicated queries?
If you use .prefetch_related it will populate the carvariant_set value, but only for a .all() query, not for a .last(), that will trigger a new query.
What we can do is define a property like:
class Car(models.Model):
manufacturer = models.ForeignKey(Manufacturer, on_delete=models.CASCADE)
name = models.CharField(max_length=300)
#property
def latest_variant(self):
items = getattr(self, '_latest_variants', ())
if items:
return items[-1]
return self.carvariant_set.last()
Then we can prefetch the related object with:
from django.db.models import Prefetch
Car.objects.prefetch_related(
Prefetch(
'carvariant_set',
queryset=CarVariant.objects.order_by('pk'),
to_attr='_latest_variants'
)
)
To get rid of duplicates you use "distinct()".
For example Car.objects.all().prefetch_related('carvariant_set').distinct(). You can read about it here:
https://docs.djangoproject.com/en/3.2/ref/models/querysets/#django.db.models.query.QuerySet.distinct
sometimes you might need to tell the "distinct" function which fields make an object distinct. By default it's the id, but you can do something like "distinct('name')" in order to avoid getting 2 instances with the same name for example.
I have two models with One-to-Many relationship; Listing, and Bids.
Is it possible to retrieve and display a list of Bid objects' bid_price in Listing's str method?
The code provided below crashes the server and I am not sure of the correct keywords to search for.
I understand how listing.bid_set works in the Shell or view, but I am not sure how to make it work here.
class Listing(models.Model):
title = models.CharField(max_length=64)
def __str__(self):
bid_objects = Bid.objects.all().filter(listing__id=self.id)
price_list = []
for bid_object in bid_objects:
price_list.append(bid_object.bid_price)
return f"{self.title}, {price_list}"
class Bid(models.Model):
listing = models.ForeignKey(Listing, on_delete=models.CASCADE, related_name="listing_bids")
bid_price = models.DecimalField(max_digits=6, decimal_places=2)
Thanks for your help.
Since you specified related_name='listing_bids', it means you access the related Bids with self.listing_bids:
class Listing(models.Model):
title = models.CharField(max_length=64)
def __str__(self):
bid_objects = self.listing_bids.values_list('bid_price', flat=True)
return f'{self.title}, {bid_objects}'
Hello guys I have one query in my Django project.
First of all, You can see that I have two Django models named BookSeller and Book
Bookseller model
class BookSeller(models.Model):
user_name = models.CharField(max_length=200)
user_email = models.CharField(max_length=200)
user_password = models.CharField(max_length=200)
user_phone = models.CharField(max_length=100)
user_photo = models.ImageField(upload_to='book/seller_photos/%Y/%m/%d/', blank=True)
user_address = models.CharField(max_length=300)
user_state = models.CharField(max_length=100)
user_city = models.CharField(max_length=100)
def __str__(self):
return self.user_name
Book Model
class Book(models.Model):
book_owner = models.ForeignKey(BookSeller, related_name='book_seller', on_delete=models.CASCADE)
book_category = models.CharField(max_length=200)
book_title = models.CharField(max_length=200)
book_price = models.IntegerField()
book_edition = models.CharField(max_length=200)
book_author = models.CharField(max_length=200)
book_old = models.IntegerField()
book_page = models.IntegerField()
book_description = models.TextField(max_length=200)
book_image_1 = models.ImageField(upload_to='book/book_photos/%Y/%m/%d', blank=True)
book_image_2 = models.ImageField(upload_to='book/book_photos/%Y/%m/%d', blank=True)
book_image_3 = models.ImageField(upload_to='book/book_photos/%Y/%m/%d', blank=True)
book_image_4 = models.ImageField(upload_to='book/book_photos/%Y/%m/%d', blank=True)
def __str__(self):
return self.book_title
Want to DO: In my project I want to find books by that book seller's city.
For example, if I write city name 'Silicon Valley' in my search field then it should show me all "Books" that's Sellers(BookSeller) belonging to Silicon Valley.
Query: So my query is how can I do that Django Query set, because I can't find out any query which can do this task.
If you guys have any other solution then please suggest me!!!
For finding the books by some book seller's city you can simly filter the Book instances like so:
Book.objects.filter(book_owner__user_city="Silicon Valley")
One other problem I noticed is that I think you misunderstand related_name attribute in ForeignKey.
The related_name attribute specifies the name of the reverse relation from the BookSeller model back to Book model.
If you don't specify a related_name, Django automatically creates one using the name of your model with the suffix _set.
For instance more appropriate related name in your FK would be books, and without defining it would default to book_set.
book_owner = models.ForeignKey(BookSeller, related_name='books', on_delete=models.CASCADE)
Here is an example, lets assume you have 1 instance of BookSeller and 2 isntances of Book with FK to that instance of BookSeller.
my_book_seller = BookSeller(...)
my_book_1 = Book(book_owner=my_book_seller, ...)
my_book_2 = Book(book_owner=my_book_seller, ...)
Now in your case doing the my_book_seller.book_seller.all() (since you defined the related_name to be book_seller) would return you the two Book instances belonging to my_book_seller. This doesn't make much sense.
On the other hand having the related_name='books' you would get the same books by doing my_book_seller.books.all().
You can find more info in docs.
You can do that like this
Book.objects.filter(book_owner__user_city="Silicon Valley")
and you learn more about various kinds of joining at
this link
You can get the desired results doing something like
books_by_seller_city = Book.objects.filter(book_owner__user_city='Silicon Valley')
Note the use of __ which tells the ORM to look at the referenced model attribute.
You can do with q look ups also, in that case you can add more fields in your query.
queryset = Book.objects.filter(Q(book_owner__user_city__icontains=query)|
.................)
I Got this Models in models.py:
class Boats(models.Model):
id = models.BigIntegerField(primary_key=True)
created = models.DateTimeField(default=timezone.now, blank=True)
name = models.CharField(max_length=30)
class Meta:
managed = True
db_table = 'boats'
ordering = ['name']
class Clients(models.Model):
id = models.BigIntegerField(primary_key=True)
created = models.DateTimeField(default=timezone.now, blank=True)
code = models.CharField(max_length=100)
class Meta:
managed = True
db_table = 'clients'
ordering = ['name']
==========================
In the views.py; my function do it like that:
f = NewBoatForm(request.POST)
if f.is_valid():
nBoat = f.save()
print 'ID:'+str(nBoat.id)
cBoat = ClientsBoats()
cBoat.client = client
cBoat.boat = nBoat
cBoat.save()
But django fails with this error:
ValueError: save() prohibited to prevent data loss due to unsaved related object 'boat'.
I print the ID but it's Null. Can someOne help me.
You've overridden the primary key field, id, to be something other than an AutoField. Don't do that.
Normally you wouldn't define it at all, and let Django do it automatically. If you are really really sure that a standard integer field is not big enough, you can use BigAutoField. But I doubt you will have more than 2147483647 boats in your database.