goutomroy

author1 = Author(name='author1')
author2 = Author(name='author2')
author3 = Author(name='author3')
entry = Entry.objects.get(id=1)

# Don't
entry.authors.add(author1)
entry.authors.add(author2)
entry.authors.add(author3)

goutomroy

# Don't
for i in range(20):
    Blog.objects.create(name="blog"+str(i), headline='tagline'+str(i))

# Do
blogs = []
for i in range(20):
    blogs.append(Blog(name="blog"+str(i), headline='tagline'+str(i)))
Blog.objects.bulk_create(blogs)

goutomroy

# Don't.Delete one by one.
for entry in Entry.objects.all():
    entry.delete()
    
# Do.Delete all at once.
Entry.objects.all().delete()

# Don't
for entry in Entry.objects.all():
    entry.likes += 1

goutomroy

# Don't
count = len(Entry.objects.all())  # Evaluates the entire queryset

# Do
count = Entry.objects.count()  # Executes more efficient SQL to determine count

# Don't
qs = Entry.objects.all()
if qs:

goutomroy

# Don't
most_liked = 0
for entry in Entry.objects.all():
    if entry.likes > most_liked:
        most_liked = entry.likes
# Do
most_liked = Entry.objects.all().aggregate(Max('likes'))['likes__max']

goutomroy

# Don't
for entry in Entry.objects.all():
    entry.likes += 1
    entry.save()
    
# Do
Entry.objects.update(likes=F('likes') + 1)

goutomroy

try:
    one_entry = Entry.objects.get(blog=2000)
except Entry.DoesNotExist:
    # query did not match to any item.
    pass
except Entry.MultipleObjectsReturned:
    # query matched multiple items.
    pass
else:

goutomroy

q = Entry.objects.filter(blog=2).exclude(body_text__icontains="food")

q1 = Entry.objects.filter(blog=2)
q2 = q1.exclude(body_text__icontains="food")
q3 = q2[:10]

goutomroy

q1 = Entry.objects.filter(blog=2)
q2 = q1.filter(headline__contains='food')
entry_list = list(q3)

goutomroy

    
  queryset = Entry.objects.all()
    for each in queryset:
        print(each.headline)
        # Hits database for blog.
        print(each.blog.name)

    for each in queryset:
        # uses cache
        print(each.headline)