Running SQL query in Django and improperly configure error

Question

We have four tables Including Category, Seller, Product, Product_Seller. Each product has one category. each seller can sell a product. Suppose you do not sell the same product multiple times and each seller sells each product at most once. We want to find products that have more than 5 sellers. and we want to find the second category that has the largest number of products. I want to run the SQL code in Django. But it has multiple errors. Please let me know how can I fix it Using ORM. Thank you for your time and consideration.

from django.db import models
from django.db import connection
class Category(models.Model):
    title = models.CharField(max_length=128)
class Seller(models.Model):
    name = models.CharField(max_length=128)
       
    product = models.ForeignKey(
    Product,
    on_delete=models.CASCADE,
    related_name='Seller'
    )
class Product(models.Model):
    category_id = models.ForeignKey(
    Category,
    on_delete=models.CASCADE,
    related_name='Product'),
    rate = models.IntegerField(blank=True, null=True)
class ProductSeller(models.Model):
    
    product_id = models.ForeignKey(product),
    seller_id = models.ForeignKey(seller),
    price = models.IntegerField(blank=True, null=True) 
cursor = connection.cursor()

cursor.execute("""
    SELECT product_id 
    FROM ProductSeller
    GROUP BY product_id 
    HAVING COUNT(product_id) > 5
""")
cursor.execute("""
SELECT category_id
FROM Product
GROUP BY category_id 
HAVING MAX(mycount)
FROM(SELECT category_id, Count(category_id) mycount
    FROM orders
    GROUP BY category_id)
AND NOT IN(SELECT category_id
FROM Product
GROUP BY category_id 
HAVING MAX(mycount)
FROM(SELECT category_id, Count(category_id) mycount
    FROM orders
    GROUP BY category_id));
""")

the errors are:

---------------------------------------------------------------------------
ImproperlyConfigured                      Traceback (most recent call last)
<ipython-input-15-bdbc27a2a35a> in <module>
      1 from django.db import models
      2 from django.db import connection
----> 3 class Category(models.Model):
      4     title = models.CharField(max_length=128)
      5 class Seller(models.Model):

~/anaconda3/lib/python3.7/site-packages/django/db/models/base.py in __new__(cls, name, bases, attrs, **kwargs)
    105 
    106         # Look for an application configuration to attach the model to.
--> 107         app_config = apps.get_containing_app_config(module)
    108 
    109         if getattr(meta, 'app_label', None) is None:

~/anaconda3/lib/python3.7/site-packages/django/apps/registry.py in get_containing_app_config(self, object_name)
    250         Return None if the object isn't in any registered app config.
    251         """
--> 252         self.check_apps_ready()
    253         candidates = []
    254         for app_config in self.app_configs.values():

~/anaconda3/lib/python3.7/site-packages/django/apps/registry.py in check_apps_ready(self)
    132             # INSTALLED_APPS raises a more helpful ImproperlyConfigured
    133             # exception.
--> 134             settings.INSTALLED_APPS
    135             raise AppRegistryNotReady("Apps aren't loaded yet.")
    136 

~/anaconda3/lib/python3.7/site-packages/django/conf/__init__.py in __getattr__(self, name)
     74         """Return the value of a setting and cache it in self.__dict__."""
     75         if self._wrapped is empty:
---> 76             self._setup(name)
     77         val = getattr(self._wrapped, name)
     78         self.__dict__[name] = val

~/anaconda3/lib/python3.7/site-packages/django/conf/__init__.py in _setup(self, name)
     59                 "You must either define the environment variable %s "
     60                 "or call settings.configure() before accessing settings."
---> 61                 % (desc, ENVIRONMENT_VARIABLE))
     62 
     63         self._wrapped = Settings(settings_module)

ImproperlyConfigured: Requested setting INSTALLED_APPS, but settings are not configured. You must either define the environment variable DJANGO_SETTINGS_MODULE or call settings.configure() before accessing settings.

Answer 1

Try this:

from django.db import models
from django.db import connection


class Category(models.Model):
    title = models.CharField(max_length=128)


class Seller(models.Model):
    name = models.CharField(max_length=128)


class Product(models.Model):
    category_id = models.ForeignKey(category),
    rate = models.IntegerField(blank=True, null=True)


class Product_Seller(models.Model):    
    product_id = models.ForeignKey(product),
    seller_id = models.ForeignKey(seller),
    price = models.IntegerField(blank=True, null=True) 

Here's an example query - but why not use the ORM? It is Django's killer feature! You'd likely have to change the table name below to be appname_product_seller, and it should be ProductSeller, not Product_Seller. Python's convention is CamelCase for Classes, and snake_case for functions, attributes, and variables.

cursor = connection.cursor()

cursor.execute("""
    SELECT product_id 
    FROM Product_Seller
    GROUP BY product_id 
    HAVING COUNT(product_id) > 5
""")

I'd recommend going through the Django tutorial if you haven't. It contains a lot of really good information.