I am using Django 2.2 and I have a model with two classes Product and ProductRevision. When I retrieve a Product, or a list of Products, I always fetch the corresponding ProductRevision. ProductRevision objects are incremented and only the last revision should be fetched with the Product.
class Product(models.Model):
name = models.CharField(max_length=50, null=False, blank=False,
verbose_name=_("name"))
product_code = models.CharField(max_length=10, null=False, blank=False,
verbose_name=_("product code"))
slug = models.SlugField(null=False, unique=True)
#property
def current_item(self):
return ProductRevision.objects.filter(product=self, active=True).order_by('-version').first()
class ProductRevision(models.Model):
product = models.ForeignKey(Product, null=True, on_delete=models.PROTECT)
version = models.IntegerField(default=0,
verbose_name=_("version"))
active = models.BooleanField(default=False, null=False, blank=True,
verbose_name=_("is active"))
qty_close = models.IntegerField(default=0,
verbose_name=_("qty of accounts to be closed"))
price_eur = models.DecimalField(max_digits=6, decimal_places=2, default=0,
verbose_name=_("price in EUR"))
I tried to add a property current_item to get the last revision of a given product. While this is working, it is very inefficient because when I use it in a template, it hits the database every time I display a field from the related ProductRevision.
I found this answer based on an old version of Django (Fetch latest related objects in django) and I'm wondering if there is no other ways to achieve the same result with current versions of Django? I'm particularly interrested in achieving this in my models.
I have managed to achieve something similar to this by using a custom prefetch related queryset
products = Product.objects.prefetch_related(Prefetch(
'productrevision_set',
queryset=ProductRevision.objects.order_by('product', '-version').distinct('product'),
to_attr='latest_revision'
))
The queryset above will only return one ProductRevision per Product which in effect gives us the latest ProductRevision for all Products in only 2 queries
for product in products:
for latest_revision in product.latest_revision:
print(product, latest_revision)
Related
I want to make a flexible online shop which will allow it's admins to create products and add custom product fields without need to program. I did it, but the final database structure is so complicated that I can't figure out how to filter it.
Let's say there are categories with some products attached to it. Each category has only one unique template, the template holds custom fields names and types(int, char). When a product is created, the corresponding template-like fields are written to another model that holds custom fields names and values.
So, how to filter the product model considering its custom fields values? To clarify, let's say someone created smartphones category, created template with fields "Brand" and "Screen size", added some smartphones and wants to filter phones with brand="Apple" and screen size > 4.5 inches.
I hope that makes sense ^_^
Database structure:
class Category(models.Model):
name = models.CharField(max_length=63)
class Product(models.Model):
category = models.ForeignKey(Category, on_delete=models.CASCADE)
name = models.CharField(max_length=63)
price = models.IntegerField(validators=[MinValueValidator(0), MaxValueValidator(1073741823)], null=True, blank=True)
#Template
class CategoryTemplate(models.Model):
category = models.ForeignKey(Category, on_delete=models.CASCADE, null=True)
name = models.CharField(max_length=255, null=True, blank=True)
#Model that holds template custom fields
class TemplateField(models.Model):
template = models.ForeignKey(CategoryTemplate, on_delete=models.CASCADE)
name = models.CharField(max_length=255, null=True, blank=True)
is_integer = models.BooleanField(blank=True, default=False)
#Values of custom char product fields
class ProductPropertiesChar(models.Model):
product = models.ForeignKey(Product, on_delete=models.CASCADE)
property_name = models.CharField(max_length=255, null=True, blank=True)
property_value = models.CharField(max_length=255, null=True, blank=True)
#Values of custom integer product fields
class ProductPropertiesInteger(models.Model):
product = models.ForeignKey(Product, on_delete=models.CASCADE)
property_name = models.CharField(max_length=255, null=True, blank=True)
property_value = models.IntegerField(validators=[MinValueValidator(0), MaxValueValidator(1073741823)], null=True, blank=True)
Maybe this will work. Firstly, I'd strongly recommed using explicit related names!
class ProductPropertiesChar(models.Model):
product = models.ForeignKey(Product, on_delete=models.CASCADE,
related_name='charprop')
...
Simple case: all Products related to a single specified ProductPropertiesChar (the default related name is too horrible to type)
results = Product.objects.filter( charprop__property_name='Brand',
charprop__property_value='Apple' )
You can combine several values with __in or use the other usual __ lookups. You should also be able to .exclude(...).
results = Product.objects.filter( charprop__property_name='Brand',
charprop__property_value__in = ['Apple','Samsung','Google'] )
You ought to be able to use Q objects
q1 = Q( charprop__property_name='Brand',charprop__property_value='Apple' )
q2 = Q( intprop__property_name='ScreenSize', intprop__property_value__gte=130 )
I'm pretty sure or will work
results = Product.objects.filter( q1 | q2 )
I'm not quite so sure about and because you are following the related name to two different objects
results = Product.objects.filter( q1 & q2 ) # not sure
You may instead need to use .intersection (doc here)
qs1 = Product.objects.filter( q1)
qs2 = Productr.objects.filter( q2)
results = qs1.intersection( qs2)
See also .union, .difference
At this poimt I'll admit I'm talking about things I have read about but never tried. You will have to experiment, and read the Django docs over and over again!
I am trying to create an E-Commerce Website and I am at the Final Step i.e. Placing the Order. So, I am trying to add all the Cart Items into my Shipment model. But I am getting this error.
'QuerySet' object has no attribute 'product'
Here are my models
class Product(models.Model):
productId = models.AutoField(primary_key=True)
productName = models.CharField(max_length=200)
productDescription = models.CharField(max_length=500)
productRealPrice = models.IntegerField()
productDiscountedPrice = models.IntegerField()
productImage = models.ImageField()
productInformation = RichTextField()
productTotalQty = models.IntegerField()
alias = models.CharField(max_length=200)
url = models.CharField(max_length=200, blank=True, null=True)
class Customer(models.Model):
user = models.OneToOneField(User, on_delete=models.CASCADE)
name = models.CharField(max_length=100, null=True, blank=True)
email = models.EmailField(max_length=100)
profileImage = models.ImageField(blank=True, null=True, default='profile.png')
phoneNumber = models.CharField(max_length=10, blank=True, null=True)
address = models.CharField(max_length=500, blank=True, null=True)
class Order(models.Model):
customer = models.ForeignKey(Customer, on_delete=models.SET_NULL, blank=True, null=True)
dateOrdered = models.DateTimeField(auto_now_add=True)
orderCompleted = models.BooleanField(default=False)
transactionId = models.AutoField(primary_key=True)
class Cart(models.Model):
product = models.ForeignKey(Product, on_delete=models.SET_NULL, blank=True, null=True)
order = models.ForeignKey(Order, on_delete=models.SET_NULL, blank=True, null=True)
quantity = models.IntegerField(default=0, blank=True, null=True)
dateAdded = models.DateTimeField(auto_now_add=True)
class Shipment(models.Model):
customer = models.ForeignKey(Customer, on_delete=models.SET_NULL, blank=True, null=True)
orderId = models.CharField(max_length=100)
products = models.ManyToManyField(Product)
orderDate = models.CharField(max_length=100)
address = models.CharField(max_length=200)
phoneNumber = models.CharField(max_length=13)
I just removed additional functions i.e. __str__ and others.
Here is the views.py
def orderSuccessful(request):
number = Customer.objects.filter(user=request.user).values('phoneNumber')
fullAddress = Customer.objects.filter(user=request.user).values('address')
timeIn = time.time() * 1000 # convert current time in milliSecond
if request.method == 'POST':
order = Shipment.objects.create(customer=request.user.customer, orderId=timeIn,
orderDate=datetime.datetime.now(), address=fullAddress,
phoneNumber=number)
user = Customer.objects.get(user=request.user)
preOrder = Order.objects.filter(customer=user)
orders = Order.objects.get(customer=request.user.customer, orderCompleted=False)
items = orders.cart_set.all() # Here is all the items of cart
for product in items:
product = Product.objects.filter(productId=items.product.productId) # error is on this line
order.products.add(product)
Cart.objects.filter(order=preOrder).delete()
preOrder.delete()
order.save()
else:
return HttpResponse("Problem in Placing the Order")
context = {
'shipment': Shipment.objects.get(customer=request.user.customer)
}
return render(request, "Amazon/order_success.html", context)
How to resolve this error and all the cart items to field products in Shipment model?
Your model is not really consistent at all. Your Cart object is an m:n (or m2m - ManyToMany) relationship between Product and Order. Usually, you would have a 1:n between Cart and Product (a cart contains one or more products). One Cart might be one Order (unless you would allow more than one carts per order). And a shipment is usually a 1:1 for an order. I do not see any of this relationships in your model.
Draw your model down and illustrate the relations between them first - asking yourself, if it should be a 1:1, 1:n or m:n? The latter can be realized with a "through" model which is necessary if you need attributes like quantities.
In this excample, we have one or more customers placing an order filling a cart with several products in different quantities. The order will also need a shipment fee.
By the way: bear in mind that "filter()" returns a list. If you are filtering on user, which is a one to one to a unique User instance, you would better use "get()" as it returns a single instance.
Putting in into a try - except or using get_object_or_404() makes it more stable.
product = Product.objects.filter(productId=items.product.productId)
should be something like:
product = product.product
not to say, it becomes obsolete.
It looks like you make a cart for a product by multiple instances of Cart, the problem is you try to access the wrong variable, also you don't need to filter again when you already have the instance, make the following changes:
carts = orders.cart_set.all() # Renamed items to carts for clarity
for cart in carts:
product = cart.product
order.products.add(product) # The name order is very misleading makes one think it is an instance of Order, actually it is an instance of Shipment
As mentioned above in my comment your variable names are somewhat misleading, please give names that make sense to any variable.
I'm building a simple application using Django where I can record and track information of a set of quality control tests performed regularly to radiotherapy and radiology equipment. It shows a list of all equipment available which I can then select to either perform a set of tests or review other activities performed previously. For now everything seems to be working. I can create new equipments, new tests and filter the tests related to that equipment. But now I'm facing a problem that I can't solve. Here is a sample of my code with the models that I'm struggling:
/models.py
class Test(models.Model):
testgroup = models.ForeignKey(TestGroup)
equipament = models.ManyToManyField(Equipament, blank=True)
number = models.CharField(max_length=10)
name = models.CharField(max_length=120)
description = models.CharField(max_length=300, null=True, blank=True)
frequency = models.ForeignKey(Frequency, null=True, blank=True)
tolerance = models.CharField(max_length=30, null=True, blank=True)
def __str__(self):
return '%s%s%s %s' % (self.testgroup.modality, self.testgroup.abbreviation, self.number, self.name)
pass
class Activity(models.Model):
CONFORMANCE_CHOICES = (
('Yes', 'Yes'),
('No', 'No'),
)
equipament = models.ForeignKey(Equipament, on_delete=models.CASCADE)
type = models.ForeignKey(Type, null=True, blank=True)
date = models.DateField(null=True, blank=True)
summary = models.CharField(max_length=30, null=True, blank=True)
user = models.CharField(max_length=50, null=True, blank=True)
test = models.ManyToManyField(Teste, blank=True)
conformance = models.CharField(max_length=10, choices=CONFORMANCE_CHOICES, null=True, blank=True)
def __str__(self):
return '%s %s' % (self.date, self.equipament)
pass
What I need to do is to be able to save a result, one of the conformance choices to each test. I am able to display in the Activity view a list of the tests I want to perform but how can I save that conformance field for each test? My best approach was to change the conformance field to a ManyToManyField and through the form create the relations between Tests and Conformance but I get for each test all the conformance choices. How can I define just one conformance choice (the selected one) to one test? Please help...
I was able to work this out. I am posting my solution. Maybe someone had or will have the same problem. To perform what I wanted I used inlinefomset_factory creating an intermediary model called Results with a ForeignKey to Activity. Everything works now.
I am trying to export all my database with a prefetch_related but I only get data from the main model.
My models:
class GvtCompoModel(models.Model):
gvtCompo= models.CharField(max_length=1000, blank=False, null=False)
...
class ActsIdsModel(models.Model):
year = models.IntegerField(max_length=4, blank=False, null=False)
...
class RespProposModel(models.Model):
respPropos=models.CharField(max_length=50, unique=True)
nationResp = models.ForeignKey('NationRespModel', blank=True, null=True, default=None)
nationalPartyResp = models.ForeignKey('NationalPartyRespModel', blank=True, null=True, default=None)
euGroupResp = models.ForeignKey('EUGroupRespModel', blank=True, null=True, default=None)
class ActsInfoModel(models.Model):
#id of the act
actId = models.OneToOneField(ActsIdsModel, primary_key=True)
respProposId1=models.ForeignKey('RespProposModel', related_name='respProposId1', blank=True, null=True, default=None)
respProposId2=models.ForeignKey('RespProposModel', related_name='respProposId2', blank=True, null=True, default=None)
respProposId3=models.ForeignKey('RespProposModel', related_name='respProposId3', blank=True, null=True, default=None)
gvtCompo= models.ManyToManyField(GvtCompoModel)
My view:
dumpDB=ActsInfoModel.objects.all().prefetch_related("actId", "respProposId1", "respProposId2", "respProposId3", "gvtCompo")
for act in dumpDB.values():
for field in act:
print "dumpDB field", field
When I display "field", I see the fields from ActsInfoModel ONLY, the starting model. Is it normal?
You haven't understood the arguments to prefetch_related. It's not a list of fields, but a list of models.
(Note that your field naming convention is also very misleading - respProposId1 and actId are not IDs, but actual instances of the models. Django has created an underlying field in each case by appending _id, so the db columns are respProposId1_id and actId_id. You should just call the fields resp_propos1 and resp_propos2 - also note that normal style is lower_case_with_underscore, not capWords.)
It is normal, that you are seeing fields from ActsInfoModel only. You can access related models via dot notation, like:
acts = ActsInfoModel.objects.all().prefetch_related("actId", "respProposId1", "respProposId2", "respProposId3", "gvtCompo")
for act in acts:
print act.respProposId1.respPropos
Related models are already prefetched, so it won't produce any additional queries. FYI, quote from docs:
Returns a QuerySet that will automatically retrieve, in a single
batch, related objects for each of the specified lookups.
I have an Event model. Events can have many 'presenters'. But each presenter can either 1 of 2 different types of profiles. Profile1 and Profile2. How do I allow both profiles to go into presenters?
This will be 100% backend produced. As to say, admin will be selecting "presenters".
(Don't know if that matters or not).
class Profile1(models.Model):
user = models.ForeignKey(User, null=True, unique=True)
first_name = models.CharField(max_length=20, null=True, blank=True)
last_name = models.CharField(max_length=20, null=True, blank=True)
created = models.DateTimeField(auto_now_add=True)
modified = models.DateTimeField(auto_now=True)
about = models.TextField(null=True, blank=True)
tags = models.ManyToManyField(Tag, null=True, blank=True)
country = CountryField()
avatar = models.ImageField(upload_to='avatars/users/', null=True, blank=True)
score = models.FloatField(default=0.0, null=False, blank=True)
organization = models.CharField(max_length=2, choices=organizations)
class Profile2(models.Model):
user = models.ForeignKey(User, null=True, unique=True)
first_name = models.CharField(max_length=20, null=True, blank=True)
last_name = models.CharField(max_length=20, null=True, blank=True)
created = models.DateTimeField(auto_now_add=True)
modified = models.DateTimeField(auto_now=True)
about = models.TextField(null=True, blank=True)
tags = models.ManyToManyField(Tag, null=True, blank=True)
country = CountryField()
avatar = models.ImageField(upload_to='avatars/users/', null=True, blank=True)
score = models.FloatField(default=0.0, null=False, blank=True)
...
class Event(models.Model):
title = models.CharField(max_length=200)
sub_heading = models.CharField(max_length=200)
presenters = ManyToManyField(Profile1, Profile2, blank=True, null=True) ?
...
# I've also tried:
profile1_presenters = models.ManyToManyField(Profile1, null=True, blank=True)
profile2_presenters = models.ManyToManyField(Profile2, null=True, blank=True)
# is there a better way to accomplish this?...
I think you have a desing problem here. In my opinion, you must think what is a Presenter and what's the different between a Presenter with "profile 1" and with "profile 2". What are you going to do with this models? Are you sure there are just two profiles? Is there any chance that, in some time from now, a different profile ("profile 3") appears? And profile 4? and profile N?
I recommend you to think again about your models and their relations. Do NOT make this decision thinking of how difficul/easy will be to handle these models from django admin. That's another problem and i'll bet that if you think your models a little bit, this won't be an issue later.
Nevertheless, i can give you some advice of how to acomplish what you want (or i hope so). Once you have think abount how to model these relations, start thinking on how are you going to write your models in django. Here are some questions you will have to answer to yourself:
Do you need one different table (if you are going to use SQL) per profile?
If you cannot answer that, try to answer these:
1) What's the difference between two different profiles?
2) Are there more than one profile?
3) Each presenter have just one profile? What are the chances that this property changes in near future?
I don't know a lot about what you need but i think the best option is to have a model "Profile" apart of your "Presenter" model. May be something like:
class Profile(models.Model):
first_profile_field = ...
second_profile_field = ...
# Each presenter have one profile. One profile can "represent"
# to none or more presenters
class Presenter(models.Model):
first_presenter_field = ....
second_presenter_field = ....
profile = models.ForeignKey(Profile)
class Event(models.Model):
presenters = models.ManyToManyField(Presenter)
....
This is just an idea of how i imagine you could design your model. Here are some links that may help you once you have design your models correctly and have answered the questions i made to you:
https://docs.djangoproject.com/en/dev/topics/db/models/#model-inheritance
https://docs.djangoproject.com/en/dev/misc/design-philosophies/#models
http://www.martinfowler.com/eaaCatalog/activeRecord.html
And to work with the admin once you decide how your design will be:
https://docs.djangoproject.com/en/dev/ref/contrib/admin/
EDIT:
If i'm not wrong, the only difference between profile 1 and 2 fields is the "organization" field. Am i right? So i recommend you to merge both models since they are almost the same. If they have different methods, or you want to add different managers or whatever, you can use the proxy option of django models. For example, you can do this:
class Profile(models.Model):
#All the fields you listed above, including the "organization" field
class GoldenProfile(models.Model):
#you can define its own managers
objects = GoldenProfileManager()
....
class Meta:
proxy = True
class SilverProfile(models.Model):
....
class Meta:
proxy = True
This way, you can define different methods or the same method with a different behaviour in each model. You can give them their own managers, etcetera.
And the event class should stay like this:
class Event(models.Model):
title = models.CharField(max_length=200)
sub_heading = models.CharField(max_length=200)
presenters = ManyToManyField(Profile, blank=True, null=True)
Hope it helps!