optimization database operations

• Understand cached attributes

>>> entry = Entry.objects.get(id=1)
>>> entry.blog   # Blog object is retrieved at this point
>>> entry.blog   # cached version, no DB access
>>> entry = Entry.objects.get(id=1)
>>> entry.authors.all()   # query performed
>>> entry.authors.all()   # query performed again

• Do database work in the database rather than in Python
• Retrieve everything at once if you know you will need it
  • Use QuerySet.select_related() and prefetch_related()
• Don’t retrieve things you don’t need
  • Use QuerySet.values() and values_list()
  • Use QuerySet.defer() and only()
  • Use QuerySet.count() rather than len(query_set)
    • if there is cache use count() equals Len()
  • Use QuerySet.exists() rather than if query_set
    • if there is cache user exists() equals if query_set
• Use QuerySet.update() and delete() rather than get query set then save
• Insert in bulk
• use create
• Don’t order results if you don’t care
• Use foreign key values directly
  • use entry.blog_id rather than entry.blog.id