Reduce memory use when obfuscating staging environment data

Django caches query results by default. See this comment from the Django docs:

  In a newly created QuerySet, the cache is empty. The first time a QuerySet is
  evaluated – and, hence, a database query happens – Django saves the query
  results in the QuerySet’s cache and returns the results that have been
  explicitly requested (e.g., the next element, if the QuerySet is being
  iterated over). Subsequent evaluations of the QuerySet reuse the cached
  results.

-- https://docs.djangoproject.com/en/5.1/topics/db/queries/#caching-and-querysets

This can result in significant memory use. The live box was running out of
memory when we were attempting to obfuscate email details, presumably because
that model contains some large text fields.

We disable caching as we only need to iterate over each queryset once and,
obviously, we need to address the issue of running out of memory.

app/core/management/commands/obfuscate_data.py

@@ -27,7 +27,7 @@ def handle(self, *args, **kwargs):
         self.stdout.write("\nObfuscating personal information...")
         disable_signals()
 
-        fake = Faker('en_AU')
+        fake = Faker("en_AU")
 
         clients = Client.objects.all()
         emails = Email.objects.all()
@@ -46,27 +46,27 @@ def handle(self, *args, **kwargs):
             | Q(is_superuser=True)
         ).distinct()
 
-        for t in tenancies:
+        for t in tenancies.iterator():
             t.address = fake.street_address()
             t.suburb = fake.city()
             t.postcode = fake.postcode()
             t.save()
 
-        for u in users:
+        for u in users.iterator():
             u.email = fake.unique.email()
-            u.username = u.email # Username same as fake email.
+            u.username = u.email  # Username same as fake email.
             u.first_name = fake.first_name()
             u.last_name = fake.last_name()
             u.save()
 
-        for p in people:
+        for p in people.iterator():
             p.full_name = fake.name()
             p.email = fake.email()
             p.address = fake.address()
             p.phone_number = fake.phone_number()
             p.save()
 
-        for c in clients:
+        for c in clients.iterator():
             c.first_name = fake.first_name()
             c.last_name = fake.last_name()
             if c.preferred_name:
@@ -75,7 +75,7 @@ def handle(self, *args, **kwargs):
             c.phone_number = fake.phone_number()
             c.save()
 
-        for i in issues:
+        for i in issues.iterator():
             if i.outcome_notes:
                 i.outcome_notes = " ".join(fake.sentences())
 
@@ -87,11 +87,11 @@ def handle(self, *args, **kwargs):
             }
             i.save()
 
-        for n in notes:
+        for n in notes.iterator():
             n.text = " ".join(fake.sentences())
             n.save()
 
-        for e in emails:
+        for e in emails.iterator():
             e.received_data = None
             e.subject = fake.sentence()
             e.text = "\n\n".join(fake.paragraphs())
@@ -104,12 +104,10 @@ def handle(self, *args, **kwargs):
                 e.from_address = fake.email()
             if e.to_address:
                 e.to_address = fake.email()
-            e.cc_addresses = [
-                fake.email() for _ in e.cc_addresses
-            ]
+            e.cc_addresses = [fake.email() for _ in e.cc_addresses]
             e.save()
 
-        for s in services:
+        for s in services.iterator():
             if s.notes:
                 s.notes = " ".join(fake.sentences())
                 s.save()
@@ -118,14 +116,15 @@ def handle(self, *args, **kwargs):
         email_attachment = os.path.join(EmailAttachment.UPLOAD_KEY, file_name)
         file_upload = os.path.join(FileUpload.UPLOAD_KEY, file_name)
 
-        bytes = fake.image(image_format='pdf')
+        bytes = fake.image(image_format="pdf")
         default_storage.save(email_attachment, BytesIO(bytes))
         default_storage.save(file_upload, BytesIO(bytes))
 
         # Replace files attached to emails
         EmailAttachment.objects.update(
             file=email_attachment, content_type="application/pdf"
         )
+
         # Replace uploaded files
         FileUpload.objects.update(file=file_upload)