diff options
Diffstat (limited to 'docs/intro/tutorial04.txt')
| -rw-r--r-- | docs/intro/tutorial04.txt | 13 |
1 files changed, 13 insertions, 0 deletions
diff --git a/docs/intro/tutorial04.txt b/docs/intro/tutorial04.txt index cf622c9aec..2d09de9579 100644 --- a/docs/intro/tutorial04.txt +++ b/docs/intro/tutorial04.txt @@ -179,6 +179,19 @@ Now, go to ``/polls/1/`` in your browser and vote in the question. You should se results page that gets updated each time you vote. If you submit the form without having chosen a choice, you should see the error message. +.. note:: + The code for our ``vote()`` view does have a small problem. It first gets + the ``selected_choice`` object from the database, then computes the new + value of ``votes``, and then saves it back to the database. If two users of + your Web site try to vote at *exactly the same time*, this might go wrong: + The same value, let's say 42, will be retrieved for ``votes``. Then, for + both users the new value of 43 is computed and saved, but 44 would be the + expected value. + + This is called a *race condition*. If you are interested, you can read + :ref:`avoiding-race-conditions-using-f` to learn how you can solve this + issue. + Use generic views: Less code is better ====================================== |