Hi Everyone,
I have some questions about how caching works in web2py. I'm not interested
at this point in understanding how to cache entire views or anything like
that - in this case, I'm interested in understanding the principles behind
how web2py implements caching:
Let's say that I have a class that accepts some arguments that is defined
like so:
class SomeClass():
def __init__(self, arg1 = None, arg2 = None, arg3 = None):
self.arg1 = arg1
self.arg2 = arg2
self.arg3 = arg3
if arg1 is not None:
self.id_attribute = 'ID Value Here' + arg1
self = cache.ram(self.id_attribute, lambda self, time=(60*60*24*
30))
return self
Now the *first* time I instantiate an object of SomeClass, say by calling:
some_object = SomeClass(arg1=123, arg2=456, arg3=789)
Then this will create an object of class "SomeClass", and (because arg1 is
not None) will save that object to the cache (in ram) with the following
attributes:
some_object.arg1 == 123
some_object.arg2 == 456
some_object.arg3 == 789
some_object.id_attribute == 'ID Value Here123'
Is the above so far correct?
If so, then what happens if I perform an operation on some_object, like so:
some_object.arg2 = 654
In this case:
A. Does the cached object get updated:
- if this statement gets executed < (60*60*24*30) seconds from when the
object was instantiated?
- if this statement gets executed > (60*60*24*30) seconds from when the
object was instantiated?
or:
B. The local object gets updated, but the cached value does not change:
- if this statement gets executed < (60*60*24*30) seconds from when the
object was instantiated?
- if this statement gets executed > (60*60*24*30) seconds from when the
object was instantiated?
or: C. Something else?
And then what happens when I have some other function try to "do something"
using some_object?
some_other_value = some_object.arg2 + 987
Specifically, does the value of some_object.arg2 get read from the cache or
from the object itself:
- if this statement gets executed < (60*60*24*30) seconds from when the
object was instantiated?
- if this statement gets executed > (60*60*24*30) seconds from when the
object was instantiated?
And finally, if I wish to force a changed value of some_object to be saved
to the cache, am I correct that I should then call:
some_object.arg3 = 1111
some_object = cache.ram(self.id_attribute, lambda self, time=0)
which will explicitly change the cached version of some_object? Does this
mean that the next time someone instantiates an object of class "SomeClass"
with the same arg1 value but a different time_expire value, the cached
object will be overwritten?
Any help / clarification / explanation would be much appreciated!
Thanks in advance,
Chris
--
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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