Fixed #29867 -- Added support for storing None value in caches. #13671
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Thanks for the review. Updated. |
smithdc1
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Dec 16, 2020
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Many of the cache operations make use of the default argument to the .get() operation to determine whether the key was found in the cache. The default value of the default argument is None, so this results in these operations assuming that None is not stored in the cache when it actually is. Adding a sentinel object solves this issue. Unfortunately the unmaintained python-memcached library does not support a default argument to .get(), so the previous behavior is preserved for the deprecated MemcachedCache backend.
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Fixes ticket-29867, supersedes #11812 and #13055
This is following on from my comments in #11812 in particular.
Many of the cache operations make use of
get()with the implicitdefault=Noneand assume that the returnedNonevalue indicates the value is not stored. This may not be true asNonecan be explicitly set into the cache. The fix is to use a sentinel object as the default in the absence of the key in the cache.Unfortunately this does not work for python-memcached, so we introduce a feature flag to keep the existing behaviour for that backend.