Django raw query giving same result on all models - django

Question

I have 3 models Product, Photo, and ProductLikeDilike. I am performing left outer join on all the 3 models. First I am joining Product with Photo and then the resultant table(temp) I am joining with ProductLikeDilike. Below is the raw sql.
Note: olx is the name of django app.
data = Product.objects.raw('select * from (select
olx_product.id,olx_product.name,olx_photo.file,olx_photo.cover_photo_flag
from olx_product left outer join olx_photo on
(olx_product.id=olx_photo.reference_id_id) where
olx_photo.cover_photo_flag="yes" or olx_photo.cover_photo_flag is null) as
temp left outer join olx_productlikedislike on
(temp.id=olx_productlikedislike.product_id_id and
olx_productlikedislike.product_liked_by_id_id=2)')
for x in data:
print(x.name)
What I want to understand that when I use any of the above 3 models to run the raw sql why I am getting the same result i.e.
When I do
data = Product.objects.raw('select *.....')
for x in data:
print(x.name)
or
data = Photo.objects.raw('select *......')
for x in data:
print(x.name)
or
data = ProductLikeDislike.raw('select *.....')
for x in data:
print(x.name)
I am getting the same result. Why?
Please help me to understand this.
Below is the models.py file
from django.db import models
from django.urls import reverse
from django.dispatch import receiver
from django.contrib.auth.models import User
class Product(models.Model):
category = models.ForeignKey(Category ,on_delete=models.CASCADE)
name = models.CharField(max_length = 200, db_index = True)
slug = models.SlugField(max_length = 200, db_index = True)
description = models.TextField(blank = True)
price = models.DecimalField(max_digits = 10, decimal_places = 2 )#Not used FloatField to avoid rounding issues
created = models.DateTimeField(auto_now_add=True)
updated = models.DateTimeField(auto_now=True)
contact= models.BigIntegerField(default=None,blank=True, null=True)
created_by = models.CharField(max_length = 200, default=None,blank=True, null=True)
uploaded_by_id = models.IntegerField(default=0)
status = models.IntegerField(default=0) # 0-->Active,1-->Inactive
mark_as_sold = models.IntegerField(default=0) # 0-->not sold,1-->sold
def get_absolute_url(self):
return reverse('olx:edit_product', kwargs={'pk': self.pk})
class Meta:
ordering = ('-created',)
index_together = (('id','slug'),)# we want to query product by id and slug using together index to improve performance
def __str__(self):
return self.name
class Photo(models.Model):
reference_id = models.ForeignKey(Product, null=True,on_delete=models.CASCADE)
photo_type = models.CharField(max_length = 70, db_index = True)
file = models.FileField(upload_to='photos/',default='NoImage.jpg')
cover_photo_flag = models.CharField(default=0,max_length = 5, db_index = True)
uploaded_at = models.DateTimeField(auto_now_add=True)
uploaded_by_id = models.IntegerField(default=0)
status = models.IntegerField(default=0) # 0-->Active,1-->Inactive
class Meta:
ordering = ('-uploaded_at',)
class ProductLikeDislike(models.Model):
product_id = models.ForeignKey(Product,models.SET_DEFAULT,default=0)
product_liked_by_id = models.ForeignKey(User,models.SET_DEFAULT,default=0)
status = models.BooleanField(default=False)
And Please also show me how to write it in pure Django way if possible?

Answer 1

I am getting the same result. Why? Please help me to understand this.
Because .raw(..) [Django-doc] just takes a raw query and executes it. The model from which the raw is performed is irrelevant.
We can generate a query that looks like:
from django.db.models import Q
Product.objects.filter(
Q(photo__photo_flag__isnull=True) | Q(photo__photo_flag='yes'),
Q(likedislike__product_liked_by_id_id=2)
)
So here we accept all Products for which a related Photo object has a flag that is NULL (this also happens in case the JOIN does not yield any flags), or the photo_flag is 'yes'). Furthermore there should be a Likedislike object where the liked_by_id_id is 2.
Note that usually a ForeignKey [Django-doc] has no _id suffix, or id_ prefix. It is also a bit "odd" that you set a default=0 for this, especially since most databases only assign strictly positive values as primary keys, and it makes no sense to inherently prefer 0 over another object anyway.

Answer 2

Something like this:
user_i_care_about = User.objects.get(username='user2')
productlikedislike_set = models.Prefetch('productlikedislike_set',
ProductLikeDislike.objects.select_related('product_liked_by') \
.filter(product_liked_by=user_i_care_about) \
.order_by('id'))
photo_set = models.Prefetch('photo_set', Photo.objects.all()) # this is here incase you need to a select_related()
products = Product.objects.prefetch_related(photo_set, productlikedislike_set) \
.filter(models.Q(photo__cover_photo_flag='yes') | models.Q(photo__isnull=True)) \
.filter(productlikedislike__product_liked_by=user_i_care_about)
Then you can use:
for product in products:
for pic in product.photo_set.all():
print(x.file.name)
# every product here WILL be liked by the user
if your models look something like this:
class Product(models.Model):
# category = models.ForeignKey(Category, on_delete=models.CASCADE) # TODO: uncomment, didnt want to model this out
name = models.CharField(max_length=200, db_index=True)
slug = models.SlugField(max_length=200, db_index=True)
description = models.TextField(blank=True)
price = models.DecimalField(max_digits=10, decimal_places=2) # Not used FloatField to avoid rounding issues # this is correct, no need to explain this, anyonw that works with django, gets this.
created = models.DateTimeField(auto_now_add=True)
updated = models.DateTimeField(auto_now=True)
contact = models.BigIntegerField(default=None,blank=True, null=True)
created_by = models.CharField(max_length=200, default=None, blank=True, null=True)
uploaded_by_id = models.IntegerField(default=0) # TODO: use ForeignKey(User) here!!!
status = models.IntegerField(default=0) # 0-->Active,1-->Inactive # TODO: learn to use `choices`
mark_as_sold = models.IntegerField(default=0) # 0-->not sold,1-->sold # TODO: there is something called `BooleanField` use it!
class Meta:
ordering = ('-created',)
index_together = (('id', 'slug'),) # we want to query product by id and slug using together index to improve performance
def get_absolute_url(self):
return reverse('olx:edit_product', kwargs={'pk': self.pk})
def __str__(self):
return self.name
class Photo(models.Model):
product = models.ForeignKey(Product, null=True,on_delete=models.CASCADE, db_column='reference_id')
photo_type = models.CharField(max_length=70, db_index=True)
file = models.FileField(upload_to='photos/', default='NoImage.jpg')
cover_photo_flag = models.CharField(default=0, max_length=5, db_index=True) # TODO: learn to use `choices`, and you use "yes" / "no" -- and the default is 0 -- FIX THIS!!
uploaded_at = models.DateTimeField(auto_now_add=True)
uploaded_by_id = models.IntegerField(default=0) # TODO: use ForeignKey(User) here!!!
status = models.IntegerField(default=0) # 0-->Active,1-->Inactive # TODO: learn to use `choices` -- perhaps just call this "is_active" and make it a bool
class Meta:
ordering = ('-uploaded_at',)
class ProductLikeDislike(models.Model):
product = models.ForeignKey(Product, models.SET_DEFAULT, default=0) # TODO: default=0?? this is pretty bad. models.ForeignKey(Product, models.SET_NULL, null=True) is much better
product_liked_by = models.ForeignKey(User, models.SET_DEFAULT, default=0, db_column='product_liked_by_id') # TODO: default=0?? this is pretty bad. models.ForeignKey(ForeignKey, models.SET_NULL, null=True) is much better
status = models.BooleanField(default=False) # TODO: rename, bad name. try something like "liked" / "disliked" OR go with IntegerField(choices=((0, 'Liked'), (1, 'Disliked')) if you have more than 2 values.
A full example WITH tests can be seen here: https://gist.github.com/kingbuzzman/05ed095d8f48c3904e217e56235af54a