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.. _ref-cache:
.. module:: trytond.cache
Cache
=====
.. class:: Cache(name[, duration[, context[, context_ignored_keys]]])
Use to cache values between server requests.
The ``name`` should be unique and it's used to identify the cache.
Usually ``<class_name>.<content_name>`` is used to make it unique.
The ``duration`` parameter defines how long a cached value stays valid but
if it is not set the value remains valid until it is cleared.
And the ``context`` parameter is used to indicate if the cache depends on
the user context and is ``True`` by default.
Keys specified in ``context_ignored_keys`` are ignored.
The cache is cleaned on :class:`~trytond.transaction.Transaction` starts and
resets on :class:`~trytond.transaction.Transaction` commit or rollback.
.. warning::
As there is no deepcopy of the values cached, they must never be mutated
after being set in or retrieved from the cache.
.. attribute:: Cache.size_limit
The maximal number of values cached.
The value comes from the entry with the same ``name`` under the ``cache``
section of the :ref:`configuration <topics-configuration>` using the
``default`` entry as default value.
.. attribute:: Cache.hit
Count the number of times the cache returned a cached value.
.. attribute:: Cache.miss
Count the number of times the cache did not contain the key.
.. classmethod:: Cache.stats()
Yield statistics for each instance.
.. method:: Cache.get(key[, default])
Retrieve the value of the key in the cache.
If a ``default`` is specified it is returned when the key is missing
otherwise it returns ``None``.
.. method:: Cache.set(key, value)
Set the ``value`` of the ``key`` in the cache.
.. method:: Cache.clear()
Clear all the keys in the cache.
.. classmethod:: Cache.clear_all()
Clear all cache instances.
.. classmethod:: Cache.sync(transaction)
Synchronize caches between servers using :class:`transaction
<trytond.transaction.Transaction>` instance.
.. method:: Cache.sync_since(value)
Return ``True`` if the last synchronization was done before ``value``.
.. classmethod:: Cache.commit(transaction)
Apply cache changes from transaction.
.. classmethod:: Cache.rollback(transaction)
Remove cache changes from transaction.
.. classmethod:: Cache.drop(dbname)
Drop all caches for named database.
.. note::
By default Tryton uses a MemoryCache, but this behaviour can be overridden
by setting a fully qualified name of an alternative class defined in the
:ref:`configuration <topics-configuration>` ``class`` of the ``cache``
section.
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