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sequtils.py
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Tue, Jul 2, 09:54

sequtils.py
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# -*- coding: utf-8 -*-
##
## This file is part of Invenio.
## Copyright (C) 2005, 2006, 2007, 2008, 2009, 2010, 2011, 2012 CERN.
##
## Invenio is free software; you can redistribute it and/or
## modify it under the terms of the GNU General Public License as
## published by the Free Software Foundation; either version 2 of the
## License, or (at your option) any later version.
##
## Invenio is distributed in the hope that it will be useful, but
## WITHOUT ANY WARRANTY; without even the implied warranty of
## MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
## General Public License for more details.
##
## You should have received a copy of the GNU General Public License
## along with Invenio; if not, write to the Free Software Foundation, Inc.,
## 59 Temple Place, Suite 330, Boston, MA 02111-1307, USA.
from invenio.dbquery import run_sql, IntegrityError
# Number of retries to insert a value in the DB storage
MAX_DB_RETRY = 10
class SequenceGenerator(object):
seq_name = None
def __init__(self):
assert self.seq_name
def _value_exists(self, value):
"""
Checks if the value exists in the storage
@param value: value to be checked in storage
@type value: string
@return: result of select SQL query
@rtype: tuple
"""
return run_sql("""SELECT seq_value FROM seqSTORE
WHERE seq_value=%s AND seq_name=%s""",
(value, self.seq_name))
def _insert_value(self, value):
"""
Inserts value into storage
@param value: value to be stored
@type value: string
@return: result of insert SQL query
@rtype: tuple
"""
run_sql("""INSERT INTO seqSTORE (seq_name, seq_value)
VALUES (%s, %s)""",
(self.seq_name, value))
def _next_value(self, *args, **kwargs):
"""
Internal implementation to calculate next value in sequence
"""
raise NotImplementedError
def next_value(self, *args, **kwargs):
"""
Get the next value in the sequence
@return: next value in sequence
@rtype: string
"""
db_retries = 0
value = None
while MAX_DB_RETRY > db_retries:
value = self._next_value(*args, **kwargs)
try:
self._insert_value(value)
break
except IntegrityError:
# The value is already in the storage, get next one
db_retries += 1
return value

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