Synnefo

# Copyright 2013 GRNET S.A. All rights reserved.

#

# Redistribution and use in source and binary forms, with or

# without modification, are permitted provided that the following

# conditions are met:

#

#   1. Redistributions of source code must retain the above

#      copyright notice, this list of conditions and the following

#      disclaimer.

#

#   2. Redistributions in binary form must reproduce the above

#      copyright notice, this list of conditions and the following

#      disclaimer in the documentation and/or other materials

#      provided with the distribution.

#

# THIS SOFTWARE IS PROVIDED BY GRNET S.A. ``AS IS'' AND ANY EXPRESS

# OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED

# WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR

# PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL GRNET S.A OR

# CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,

# SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT

# LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF

# USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED

# AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT

# LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN

# ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE

# POSSIBILITY OF SUCH DAMAGE.

#

# The views and conclusions contained in the software and

# documentation are those of the authors and should not be

# interpreted as representing official policies, either expressed

# or implied, of GRNET S.A.

from django.db import transaction

# USAGE

# =====

# @transaction_context()

# def a_view(args, ctx=None):

#     ...

#     if ctx:

#         ctx.mark_rollback()

#     ...

#     return http response

#

# OR (more cleanly)

#

# def a_view(args):

#     with transaction_context() as ctx:

#         ...

#         ctx.mark_rollback()

#         ...

#         return http response

def transaction_context(**kwargs):

    return TransactionHandler(ctx=TransactionContext, **kwargs)

class TransactionContext(object):

    def __init__(self, **kwargs):

        self._rollback = False

    def mark_rollback(self):

        self._rollback = True

    def is_marked_rollback(self):

        return self._rollback

    def postprocess(self):

        pass

class TransactionHandler(object):

    def __init__(self, ctx=None, allow_postprocess=True, using=None, **kwargs):

        self.using             = using

        self.db                = (using if using is not None

                                  else transaction.DEFAULT_DB_ALIAS)

        self.ctx_class         = ctx

        self.ctx_kwargs        = kwargs

        self.allow_postprocess = allow_postprocess

    def __call__(self, func):

        def wrap(*args, **kwargs):

            ctx = self.__enter__()

            kwargs['ctx'] = ctx

            typ = value = trace = None

            result = None

            try:

                result = func(*args, **kwargs)

            except Exception as e:

                typ = type(e)

                value = e

                trace = None

            finally:

                silent = self.__exit__(typ, value, trace)

                if not silent and value:

                    raise value

            return result

        return wrap

    def __enter__(self):

        db = self.db

        transaction.enter_transaction_management(using=db)

        transaction.managed(True, using=db)

        self.ctx = self.ctx_class(self.ctx_kwargs)

        return self.ctx

    def __exit__(self, type, value, traceback):

        db = self.db

        trigger_postprocess = False

        try:

            if value is not None: # exception

                if transaction.is_dirty(using=db):

                    transaction.rollback(using=db)

            else:

                if transaction.is_dirty(using=db):

                    if self.ctx.is_marked_rollback():

                        transaction.rollback(using=db)

                    else:

                        try:

                            transaction.commit(using=db)

                        except:

                            transaction.rollback(using=db)

                            raise

                        else:

                            trigger_postprocess = True

                # postprocess,

                # even if there was nothing to commit

                # as long as it's not marked for rollback

                elif not self.ctx.is_marked_rollback():

                    trigger_postprocess = True

        finally:

            transaction.leave_transaction_management(using=db)

            # checking allow_postprocess is needed

            # in order to avoid endless recursion

            if trigger_postprocess and self.allow_postprocess:

                with TransactionHandler(ctx=self.ctx_class,

                                        allow_postprocess=False,

                                        using=self.using,

                                        **self.ctx_kwargs):

                    self.ctx.postprocess()