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class User(models.Model):
  id = models.UUIDField(primary_key=True, default=uuid.uuid4, editable=False)
  name = models.TextField()
  email = models.TextField()
  age = models.PositiveSmallIntegerField()
  team = models.ForeignKey(Team, on_delete=models.PROTECT, related_name='users', null=True)
  
  
class Team(models.Model):
  location = models.TextField()

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user_query = User.objects.filter(name="Ana") # Filter the users by the name "Ana"
user_query = user_query.filter(age__lte=50) # Then get only the users where the age is less than 50
user_query = user_query.exclude(email__isnull=True) # And exclude the users that doesn't have an email
print(user_query)

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# Iteration
for user in User.objects.all():
  print(user.name)

# Slicing
User.objects.all()[:10]

# Pickling or Caching
pickle_str = pickle.dumps(user_queryset)
user_queryset = pickle.loads(pickle_str)

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# Create the query filtering users with email [email protected]
users = User.objects.get(email="[email protected]")
users.name   # Hit the database and retrive the name value
users.name   # cached version, no database access

# Create the query filtering teams named tigers
team = Team.objects.get(name="tigers")
team.users.all()   # query performed
team.users.all()   # query performed again

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# Create the query filtering users with email [email protected]
users = User.objects.get(email="[email protected]")
users.name # Hit the database and retrieve the name value
users.name # cached version, no database access

valerybriz

# Create the query filtering teams named tigers
team = Team.objects.get(name="tigers")
team.users.all() # query performed
team.users.all() # query performed again

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for user in User.objects.exclude(email__isnull=True).iterator():
  print(user.name)

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user_queryset = User.objects.all()
# The first hit to the database confirms if at least one object exists.
if user_queryset.exists():
  # Another database hit to start fetching the rows in batches.
  for user in user_queryset.iterator():
    print(user.name)

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Team.objects.all().prefetch_related('users')

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# Hits the database
team_queryset = Team.objects.get(name="tigers")
# Hits the database again to get the related User objects
user = team_queryset.user