transactions.rst

Transactions

Like any database worth its salt, SQLite supports transactions. Axiom exposes these through the store's transact method.

The transact method takes a function. That function will be run in a database transaction. The changes in the function happen atomically (that is: either they entirely do or entirely don't).

.. testsetup::

    from axiom.store import Store
    from bunny import Bunny

>>> store = Store()
>>> thumper = Bunny(store=store)
>>> bugs = Bunny(store=store)
>>> def petBunny():
...     bugs.timesPetted += 1
...     thumper.timesPetted += 1
>>> store.transact(petBunny)
>>> assert thumper.timesPetted == bugs.timesPetted == 1

Any uncaught exception raised by the transacted function will be reraised. When this happens, the changes are reset to what they were before the transaction was initiated.

>>> assert thumper.timesPetted == 1
>>> def runIntoProblems():
...     thumper.timesPetted += 1
...     raise RuntimeError("fluffiness overload")
>>> store.transact(runIntoProblems)
Traceback (most recent call last):
...
RuntimeError: fluffiness overload
>>> assert thumper.timesPetted == 1

The transact method takes any amount of arguments (which are passed verbatim to the transacted function), and will return the return value of the transacted function.

>>> def petBunnies(bunnies, times):
...     totalPetsGiven = 0
...     for bunny in bunnies:
...         bunny.timesPetted += times
...         totalPetsGiven += times
...     return totalPetsGiven
>>> store.transact(petBunnies, [thumper, bugs], 2)
4