107 lines
3.2 KiB
Python
107 lines
3.2 KiB
Python
"""
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Core methods
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------------
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.. autofunction:: cache_toolbox.core.get_instance
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.. autofunction:: cache_toolbox.core.delete_instance
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.. autofunction:: cache_toolbox.core.instance_key
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"""
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from django.core.cache import cache
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from django.db import DEFAULT_DB_ALIAS
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from . import app_settings
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def get_instance(model, instance_or_pk, timeout=None, using=None):
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"""
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Returns the ``model`` instance with a primary key of ``instance_or_pk``.
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If the data is cached it will be returned from there, otherwise the regular
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Django ORM is queried for this instance and the data stored in the cache.
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If omitted, the timeout value defaults to
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``settings.CACHE_TOOLBOX_DEFAULT_TIMEOUT`` instead of 0 (zero).
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Example::
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>>> get_instance(User, 1) # Cache miss
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<User: lamby>
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>>> get_instance(User, 1) # Cache hit
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<User: lamby>
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>>> User.objects.get(pk=1) == get_instance(User, 1)
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True
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"""
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pk = getattr(instance_or_pk, 'pk', instance_or_pk)
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key = instance_key(model, instance_or_pk)
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data = cache.get(key)
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if data is not None:
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try:
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# Try and construct instance from dictionary
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instance = model(pk=pk, **data)
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# Ensure instance knows that it already exists in the database,
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# otherwise we will fail any uniqueness checks when saving the
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# instance.
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instance._state.adding = False
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# Specify database so that instance is setup correctly. We don't
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# namespace cached objects by their origin database, however.
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instance._state.db = using or DEFAULT_DB_ALIAS
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return instance
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except:
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# Error when deserialising - remove from the cache; we will
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# fallback and return the underlying instance
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cache.delete(key)
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# Use the default manager so we are never filtered by a .get_query_set()
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# import logging
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# log = logging.getLogger("tracking")
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# log.info( str(pk) )
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instance = model._default_manager.using(using).get(pk=pk)
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data = {}
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for field in instance._meta.fields:
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# Harmless to save, but saves space in the dictionary - we already know
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# the primary key when we lookup
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if field.primary_key:
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continue
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if field.get_internal_type() == 'FileField':
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# Avoid problems with serializing FileFields
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# by only serializing the file name
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file = getattr(instance, field.attname)
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data[field.attname] = file.name
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else:
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data[field.attname] = getattr(instance, field.attname)
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if timeout is None:
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timeout = app_settings.CACHE_TOOLBOX_DEFAULT_TIMEOUT
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cache.set(key, data, timeout)
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return instance
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def delete_instance(model, *instance_or_pk):
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"""
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Purges the cache keys for the instances of this model.
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"""
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cache.delete_many([instance_key(model, x) for x in instance_or_pk])
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def instance_key(model, instance_or_pk):
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"""
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Returns the cache key for this (model, instance) pair.
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"""
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return '%s.%s:%d' % (
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model._meta.app_label,
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model._meta.module_name,
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getattr(instance_or_pk, 'pk', instance_or_pk),
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)
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