Unable to Understand the below statements of models in Django - django

Question

I am naive in Django, I have done a sample E-commerce application that is present online. I am unable to understand the highlighted statements, I searched online but unable to understand the statements.
Can someone please explain me like below
productitems = self.name_set.all()
From where this name_set.all() came ?????????
orderItems = self.orderitem_set.all()
likewise from where orderitem_set.all() ?????????
from django.db import models
from django.contrib.auth.models import User
# Create your models here.
class Customer(models.Model):
user = models.OneToOneField(User,on_delete=models.CASCADE, null=True,blank=True)
name = models.CharField(max_length=200,null=True)
email = models.CharField(max_length=200,null=True)
def __str__(self):
return self.name
class Product(models.Model):
name = models.CharField(max_length=200, null=True)
price = models.DecimalField(max_digits=7,decimal_places=2)
digital = models.BooleanField(default=False,null=True,blank=False)
image = models.ImageField(null=True,blank=True)
#image
def __str__(self):
return self.name
#property
def imageURL(self):
try:
url = self.image.url
except:
url = ''
return url
#property
def get_product_total(self):
**productitems = **self.name_set.all()****
total = sum([item.get_total for item in productitems])
return total
print('total:',total)
class Order(models.Model):
customer = models.ForeignKey(Customer,on_delete=models.SET_NULL,blank=True,null=True)
date_ordered=models.DateTimeField(auto_now_add=True)
complete = models.BooleanField(default=False,null=True,blank=False)
transaction_id = models.CharField(max_length=200, null=True)
def __str__(self):
return str(self.id)
#property
def shipping(self):
shipping = False
orderItems = **self.orderitem_set.all()**
for i in orderItems:
if i.product.digital == False:
shipping = True
return shipping
#property
def get_cart_total(self):
orderitems = self.orderitem_set.all()
total = sum([item.get_total for item in orderitems])
return total
#property
def get_cart_items(self):
orderitems = self.orderitem_set.all()
total = sum([item.quantity for item in orderitems])
return total
class OrderItem(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)
date_added=models.DateTimeField(auto_now_add=True)
def __str__(self):
return str(self.product)
#property
def get_total(self):
print(self.product.price)
# print("self.product.price:",self.product.price)
# print("self.quantity:", self.quantity)
total = self.product.price * self.quantity
return total
class ShippingAddress(models.Model):
customer = models.ForeignKey(Customer,on_delete=models.SET_NULL,blank=True,null=True)
order = models.ForeignKey(Order, on_delete=models.SET_NULL, blank=True, null=True)
address = models.CharField(max_length=200,null=True)
city = models.CharField(max_length=200, null=True)
state = models.CharField(max_length=200, null=True)
zipcode = models.CharField(max_length=200, null=True)
date_added = models.DateTimeField(auto_now_add=True)
def __str__(self):
return str(self.address)

Answer 1

Those are reverse foreign key lookups. The {field_name}_set pattern is what Django uses by default if you don't define a different term yourself.
The Django documentation explains it more here https://docs.djangoproject.com/en/3.1/ref/models/fields/#django.db.models.ForeignKey.related_name
and here https://docs.djangoproject.com/en/3.1/topics/db/queries/#following-relationships-backward
An example from the docs is:
>>> b = Blog.objects.get(id=1)
>>> b.entry_set.all() # Returns all Entry objects related to Blog.
Instead of using the default you can set the related lookup to a custom value when defining the ForeignKey field on the model, using the related_name argument. I do this often myself, there are usually more fitting terms for the project than the default.