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nested transactions context manager and decorator

Author:
demanzano
Posted:
August 18, 2011
Language:
Python
Version:
1.3
Tags:
decorator nested transaction contextmanager
Score:
0 (after 0 ratings)

This is a modification of Django 1.3's transaction.commit_on_success() decorator and context manager. It's inspired by snippet 1343 which unfortunately don't work in current Django neither as a context manager.

In my junior projects it works fine but I've not tested in critical projects yet! YMMV !

How it works: it simply counts the nesting level and does the real transaction enter/exit only on first call and last call respectively (code copied from Django's commit_on_success() ). It use thread local storage to save the per-thread nesting level count safely.

To use it just put the code in a file (i.e. nested_commit_on_success.py) and import and use it exacly as normal commit_on_success(), both as decorator (@nested_commit_success) or context manager (with nested_commit_on_success(): ).

Any feedback is welcome!

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from django.db.transaction import managed, enter_transaction_management, is_dirty, rollback, commit, leave_transaction_management, _transaction_func

import threading

# storage of nested count
_tl = threading.local()

def nested_commit_on_success(using=None):

   def entering(using):
     lev = getattr(_tl,"level",0)
     lev += 1
     _tl.level = lev
     if lev >= 2: # is it nested ?
       return # yes it's nested, do nothing
     else:
       # first time, enter transaction
       enter_transaction_management(using=using)
       managed(True, using=using)

   def exiting(exc_value, using):
     lev = _tl.level
     _tl.level -= 1
     if lev >= 2: # is it nested ?
       return # yes, do nothing
     # last time, must do correct transaction ending
     try:
         if exc_value is not None:
             if is_dirty(using=using):
                 rollback(using=using)
         else:
             if is_dirty(using=using):
                 try:
                     commit(using=using)
                 except:
                     rollback(using=using)
                     raise
     finally:
         leave_transaction_management(using=using)

   return _transaction_func(entering, exiting, using)

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