141 lines
5.2 KiB
Plaintext
141 lines
5.2 KiB
Plaintext
==============================
|
|
Managing database transactions
|
|
==============================
|
|
|
|
Django gives you a few ways to control how database transactions are managed.
|
|
|
|
Django's default transaction behavior
|
|
=====================================
|
|
|
|
The default behavior of Django is to commit on special model functions. If you
|
|
call ``model.save()`` or ``model.delete()``, that change will be committed immediately.
|
|
|
|
This is much like the auto-commit setting for most databases: as soon as you
|
|
perform an action that needs to write to the database, Django produces the
|
|
insert/update/delete statements and then does the commit. There is no implicit
|
|
rollback in Django.
|
|
|
|
Tying transactions to HTTP requests
|
|
===================================
|
|
|
|
A useful way to handle transactions is to tie them to the request and response
|
|
phases.
|
|
|
|
When a request starts, you start a transaction. If the response is produced
|
|
without problems, any transactions are committed. If the view function produces
|
|
and exception, a rollback happens. This is one of the more intuitive ways to
|
|
handle transactions. To activate this feature, just add the
|
|
``TransactionMiddleware`` middleware to your stack::
|
|
|
|
MIDDLEWARE_CLASSES = (
|
|
"django.middleware.common.CommonMiddleware",
|
|
"django.middleware.sessions.SessionMiddleware",
|
|
"django.middleware.cache.CacheMiddleware",
|
|
"django.middleware.transaction.TransactionMiddleware",
|
|
)
|
|
|
|
The order is quite important: the transaction middleware will be relevant not
|
|
only for the view functions called, but for all middleware modules that come
|
|
after it. So if you use the session middleware after the transaction middleware,
|
|
session creation will be part of the transaction.
|
|
|
|
The cache middleware isn't affected as it uses it's own database cursor (that is
|
|
mapped to it's own database connection internally) and only the database based
|
|
cache is affected.
|
|
|
|
Controlling transaction management in views
|
|
===========================================
|
|
|
|
For many people, implicit request-based transactions will work wonderfully.
|
|
However, if you need to control the way that transactions are managed,
|
|
there are a set of decorators that you can apply to a function to change
|
|
the way transactions are handled.
|
|
|
|
.. note::
|
|
|
|
Although the examples below use view functions as examples, these
|
|
decorators can be applied to non-view functions as well.
|
|
|
|
``autocommit``
|
|
--------------
|
|
|
|
You can use the ``autocommit`` decorator to switch a view function to the
|
|
default commit behavior of Django, regardless of the global setting. Just use
|
|
the decorator like this::
|
|
|
|
from django.db.transaction import autocommit
|
|
|
|
@transaction.autocommit
|
|
def viewfunc(request):
|
|
....
|
|
|
|
Within ``viewfunc`` transactions will be comitted as soon as you call
|
|
``model.save()``, ``model.delete()``, or any similar function that writes to the
|
|
database.
|
|
|
|
``commit_on_success``
|
|
---------------------
|
|
|
|
You can use the ``commit_on_success`` decorator to use a single transaction for
|
|
all the work done in a function::
|
|
|
|
from django.db.transaction import commit_on_success
|
|
|
|
@commit_on_success
|
|
def viewfunc(request):
|
|
....
|
|
|
|
If the function returns successfully then all work done will be committed. If an
|
|
exception is raised beyond the function, however, the transaction will be rolled
|
|
back.
|
|
|
|
``commit_manually``
|
|
-------------------
|
|
|
|
Sometimes you need full control over your transactions. In that case, you can use the
|
|
``commit_manually`` decorator which will make you run your own transaction management.
|
|
|
|
If you don't commit or rollback and did change data (so that the current transaction
|
|
is marked as dirty), you will get a ``TransactionManagementError`` exception saying so.
|
|
|
|
Manual transaction management looks like::
|
|
|
|
from django.db import transaction
|
|
|
|
@transaction.commit_manually
|
|
def viewfunc(request):
|
|
...
|
|
# You can commit/rollback however and whenever you want
|
|
transaction.commit()
|
|
...
|
|
|
|
# But you've got to remember to do it yourself!
|
|
try:
|
|
...
|
|
except:
|
|
transaction.rollback()
|
|
else:
|
|
transaction.commit()
|
|
|
|
..admonition:: An important note to users of earlier django releases:
|
|
|
|
The database ``connection.commit`` and ``connection.rollback`` functions
|
|
(also called ``db.commit`` and ``db.rollback`` in 0.91 and earlier), no
|
|
longer exist and have been replaced by the ``transaction.commit`` and
|
|
``transaction.rollback`` commands.
|
|
|
|
How to globally deactivate transaction management
|
|
=================================================
|
|
|
|
Control freaks can totally disable all transaction management by setting
|
|
``DISABLE_TRANSACTION_MANAGEMENT`` to ``True`` in your settings file.
|
|
|
|
If you do this, there will be no management whatsoever. The middleware will no
|
|
longer implicitly commit transactions, and you'll need to roll management
|
|
yourself. This even will require you to commit changes done by middleware
|
|
somewhere else.
|
|
|
|
Thus, this is best used in situations where you want to run your own transaction
|
|
controlling middleware or do something really strange. In almost all situations
|
|
you'll be better off using the default behavior or the transaction middleware
|
|
and only modify selected functions as needed. |