Race conditions in django

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Django 1.4+ supports select_for_update, in earlier versions you may execute raw SQL queries e.g. select ... for update which depending on underlying DB will lock the row from any updates, you can do whatever you want with that row until the end of transaction. e.g.

from django.db import transaction

@transaction.commit_manually()
def add_points(request):
    user = User.objects.select_for_update().get(id=request.user.id)
    # you can go back at this point if something is not right 
    if user.points > 1000:
        # too many points
        return
    user.points += calculate_points(user)
    user.save()
    transaction.commit()

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