===========================
Data Caching in the Request
===========================

$Id$

  >>> from cybertools.zutil.rcache import rcache, rcacheproperty

  >>> class View(object):
  ...     def __init__(self, context, request):
  ...         self.context = context
  ...         self.request = request
  ...
  ...     @rcache
  ...     def calculate(self):
  ...         print 'calculating'
  ...         return 42
  ...
  ...     @rcacheproperty
  ...     def value(self):
  ...         print 'calculating'
  ...         return 43

  >>> from zope.publisher.browser import TestRequest
  >>> request = TestRequest()

When we first call the calculation method it gets executed.

  >>> v1 = View(None, request)
  >>> v1.calculate()
  calculating
  42

Subsequent calls just fetch the value from the cache.

  >>> v1.calculate()
  42

Even if we create a new view object (with the same request as before) the
value is just taken from the cache.

  >>> v2 = View(None, request)
  >>> v2.calculate()
  42

Let's now have a look at the case where the result of the calculation is
stored immediately in the view, as an instance attribute (property).

  >>> v1.value
  calculating
  43
  >>> v1.value
  43

  >>> v2.value
  43

If we associate a new request with the view the calculation is done again
when using the method.

  >>> v1.request = TestRequest()
  >>> v1.calculate()
  calculating
  42

If we use the property the value is taken direktly from the instance.

  >>> v1.value
  43
