[Erp5-dev] caching per object

[Jerome Perrin]

On Thu, Sep 14, 2006 at 09:04:29PM +0200, Bartek Gorny wrote:
> Hello
> 
> I tried to use caching methods, but it seems that a simple statement like:
> 
>  def getWhatever(self):
>    def cached_getWhatever():
>      return something
>   cached_getWhatever=CachingMethod(cached_getWhatever, id='an_id')
>   return cached_getWhatever()
> 
> does caching per portal type, which is very useful, but I need to do
> caching per object - is there any way to do this?
>

This is actually does "global" caching. Cache keys are parameters you pass
when calling the (wrapped) method.

To have a per portal type cache, you need:

 def getWhatever(self):
   def cached_getWhatever(portal_type=None):
     return something
  cached_getWhatever=CachingMethod(cached_getWhatever, id='an_id')
  return cached_getWhatever(portal_type=self.getPortalType())

Note that portal_type parameter can be ignored by the 'real' method.

In the same way, you can imagine having per object caching passing
object uid:

 def getWhatever(self):
   def cached_getWhatever(uid=None):
     return something
  cached_getWhatever=CachingMethod(cached_getWhatever, id='an_id')
  return cached_getWhatever(uid=self.getUid())

But I'm not sure it's a good idea, because if you have too much cache
keys, the whole caching mechanism will become inneficiant.

So, to make it simple, you will probably achive better performance with
a volatile attribute:
 
 def getWhatever(self):
   whatever = getattr(self, '_v_whatever', _MARKER)
   if whatever is _MARKER:
     self._v_whatever = whatever = self.computeWhatever()
   return whatever

Jerome