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# Copyright (C) 2010 Google Inc. All rights reserved.
#
# Redistribution and use in source and binary forms, with or without
# modification, are permitted provided that the following conditions are
# met:
#
# * Redistributions of source code must retain the above copyright
# notice, this list of conditions and the following disclaimer.
# * 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.
# * Neither the name of Google Inc. nor the names of its
# contributors may be used to endorse or promote products derived from
# this software without specific prior written permission.
#
# THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
# "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 THE COPYRIGHT
# OWNER 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.
from datetime import datetime
import logging
from google.appengine.ext import db
MAX_DATA_ENTRY_PER_FILE = 10
MAX_ENTRY_LEN = 1000 * 1000
class DataEntry(db.Model):
"""Datastore entry that stores one segmant of file data
(<1000*1000 bytes).
"""
data = db.BlobProperty()
@classmethod
def get(cls, key):
return db.get(key)
def get_data(self, key):
return db.get(key)
class DataStoreFile(db.Model):
"""This class stores file in datastore.
If a file is oversize (>1000*1000 bytes), the file is split into
multiple segments and stored in multiple datastore entries.
"""
name = db.StringProperty()
data_keys = db.ListProperty(db.Key)
# keys to the data store entries that can be reused for new data.
# If it is emtpy, create new DataEntry.
new_data_keys = db.ListProperty(db.Key)
date = db.DateTimeProperty(auto_now_add=True)
data = None
def delete_data(self, keys=None):
if not keys:
keys = self.data_keys
for key in keys:
data_entry = DataEntry.get(key)
if data_entry:
data_entry.delete()
def save_data(self, data):
if not data:
logging.warning("No data to save.")
return False
if len(data) > (MAX_DATA_ENTRY_PER_FILE * MAX_ENTRY_LEN):
logging.error("File too big, can't save to datastore: %dK",
len(data) / 1024)
return False
start = 0
# Use the new_data_keys to store new data. If all new data are saved
# successfully, swap new_data_keys and data_keys so we can reuse the
# data_keys entries in next run. If unable to save new data for any
# reason, only the data pointed by new_data_keys may be corrupted,
# the existing data_keys data remains untouched. The corrupted data
# in new_data_keys will be overwritten in next update.
keys = self.new_data_keys
self.new_data_keys = []
while start < len(data):
if keys:
key = keys[0]
data_entry = DataEntry.get(key)
if not data_entry:
logging.warning("Found key, but no data entry: %s", key)
data_entry = DataEntry()
else:
data_entry = DataEntry()
data_entry.data = db.Blob(data[start: start + MAX_ENTRY_LEN])
try:
data_entry.put()
except Exception, err:
logging.error("Failed to save data store entry: %s", err)
if keys:
self.delete_data(keys)
return False
logging.info("Data saved: %s.", data_entry.key())
self.new_data_keys.append(data_entry.key())
if keys:
keys.pop(0)
start = start + MAX_ENTRY_LEN
if keys:
self.delete_data(keys)
temp_keys = self.data_keys
self.data_keys = self.new_data_keys
self.new_data_keys = temp_keys
self.data = data
return True
def load_data(self):
if not self.data_keys:
logging.warning("No data to load.")
return None
data = []
for key in self.data_keys:
logging.info("Loading data for key: %s.", key)
data_entry = DataEntry.get(key)
if not data_entry:
logging.error("No data found for key: %s.", key)
return None
data.append(data_entry.data)
self.data = "".join(data)
return self.data
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