hem....... cache.ram behaves differently than ANY other backend because it
just stores a reference to the computed value .
That's why you can do a dict.update() without setting explicitely a new
cached value....... but you'd need to do if you see it from a "flow"
perspective.
What you are tryng to do in pseudo code is really:
.... if something_happens:
search_cached_value
if cached_value is not there:
calculate cached_value for all
store it in cache
if just_a_piece_isn't_there:
fetch_cached_value
update_a_piece_of_it
store updated_cached_value into cache
and it is what you need to do with anything not being cache.ram (i.e. fetch
"all", update a piece, store "the new all")
This difference of behaviours, and the lack of proper shortcuts is one of
the things I hate most from web2py's cache behaviour (which has some pros,
but lots of cons, like in your case). API for this kind of operations isn't
really straightforward...
Wrapping things up....
if 'foo' not in globals():
fetching = cache.whatever_but_not_ram('thekey', lambda:1,
time_expire=None) # special case to never refresh the value
if fetching == 1:
# nobody ever stored something here
huge_thing_to_compute = cache.whatever_but_not_ram('thekey',
lambda: long_cache_func(), time_expire=0) #special case to ALWAYS refresh
the value
else:
# something is stored here
if needs_updating:
fetching[just_a_piece] = 'newpiecevalue'
cache.whatever_but_not_ram('thekey', lambda: fetching,
time_expire=0)
BTW: I'm the only one thinking that you're overcomplicating the issue ?
Just store pieces in cache and let them refresh when needed without dealing
with the whole object and its relative invalidation (plus global escalation
of local variables, etc etc etc)
BTW2: if you ask to store keys indefinitely, redis is happy to persist
them. While cache.ram and cache.disk will effectively NEVER delete the
values, redis has a strict upper value of one day (24*60*60) to avoid stale
records everywhere.
--
Resources:
- http://web2py.com
- http://web2py.com/book (Documentation)
- http://github.com/web2py/web2py (Source code)
- https://code.google.com/p/web2py/issues/list (Report Issues)
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