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backend.py
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Mon, Sep 9, 21:46

backend.py
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# -*- coding: utf-8 -*-
#
# This file is part of Invenio.
# Copyright (C) 2005, 2006, 2007, 2008, 2009, 2010, 2011, 2012, 2015 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.
"""sequencegenerator backend."""
from invenio.legacy.dbquery import run_sql
from sqlalchemy.exc import IntegrityError
# Number of retries to insert a value in the DB storage
MAX_DB_RETRY = 10
class SequenceGenerator(object):
"""Sequence generator."""
seq_name = None
def __init__(self):
"""Init."""
assert self.seq_name
def _value_exists(self, value):
"""Check 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):
"""Insert 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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