48 lines
1.6 KiB
Python
48 lines
1.6 KiB
Python
# vim: tabstop=4 shiftwidth=4 softtabstop=4
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#
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# Licensed under the Apache License, Version 2.0 (the "License"); you may
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# not use this file except in compliance with the License. You may obtain
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# a copy of the License at
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#
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# http://www.apache.org/licenses/LICENSE-2.0
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#
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# Unless required by applicable law or agreed to in writing, software
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# distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
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# WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
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# License for the specific language governing permissions and limitations
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# under the License.
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class Timestamp(object):
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'''
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A descriptor for fetching an up-to-date timestamp from the database.
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'''
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def __init__(self, db_fetch, attribute):
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'''
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Initialise with a function to fetch the database representation of an
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object (given a context and ID) and the name of the attribute to
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retrieve.
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'''
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self.db_fetch = db_fetch
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self.attribute = attribute
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def __get__(self, obj, obj_class):
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'''
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Get the latest data from the database for the given object and class.
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'''
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if obj is None or obj.id is None:
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return None
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o = self.db_fetch(obj.context, obj.id)
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o.refresh(attrs=[self.attribute])
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return getattr(o, self.attribute)
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def __set__(self, obj, timestamp):
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'''Update the timestamp for the given object.'''
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if obj.id is None:
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raise AttributeError("%s has not yet been created" % str(obj))
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o = self.db_fetch(obj.context, obj.id)
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o.update_and_save({self.attribute: timestamp})
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