add utility for caching values in the request

git-svn-id: svn://svn.cy55.de/Zope3/src/cybertools/trunk@3791 fd906abe-77d9-0310-91a1-e0d9ade77398

zutil/rcache.py

@@ -0,0 +1,60 @@
+#
+#  Copyright (c) 2010 Helmut Merz helmutm@cy55.de
+#
+#  This program is free software; you can redistribute it and/or modify
+#  it under the terms of the GNU General Public License as published by
+#  the Free Software Foundation; either version 2 of the License, or
+#  (at your option) any later version.
+#
+#  This program is distributed in the hope that it will be useful,
+#  but WITHOUT ANY WARRANTY; without even the implied warranty of
+#  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+#  GNU General Public License for more details.
+#
+#  You should have received a copy of the GNU General Public License
+#  along with this program; if not, write to the Free Software
+#  Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
+#
+
+"""
+A simple mechanism for caching values in the request.
+
+$Id$
+"""
+
+
+INVALID = object()
+
+
+def caching(self, method, id):
+    annot = self.request.annotations
+    item = annot.setdefault('cybertools.util.rcache', {})
+    value = item.get(id, INVALID)
+    if value is INVALID:
+        value = method()
+        item[id] = value
+    return value
+
+
+def requestCache(method):
+    def _cache(self):
+        return caching(self, method, method.__name__)
+    return _cache
+
+rcache = requestCache
+
+
+class requestCacheProperty(object):
+
+    def __init__(self, func):
+        self.func = func
+
+    def __get__(self, inst, class_):
+        if inst is None:
+            return self
+        id = self.func.__name__
+        value = caching(inst, self.func, id)
+        inst.__dict__[id] = value
+        return value
+
+rcacheproperty = requestCacheProperty

zutil/rcache.txt

@@ -0,0 +1,69 @@
+============
+Data Caching
+============
+
+$Id$
+
+  >>> from cybertools.zutil.rcache import rcache, rcacheproperty
+
+  >>> class View(object):
+  ...     def __init__(self, context, request):
+  ...         self.context = context
+  ...         self.request = request
+  ...
+  ...     @rcache
+  ...     def calculate():
+  ...         print 'calculating'
+  ...         return 42
+  ...
+  ...     @rcacheproperty
+  ...     def value():
+  ...         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.
+
+  >>> 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

zutil/tests.py

@@ -19,7 +19,8 @@ def test_suite():
         #unittest.makeSuite(Test),  # we don't need this
         #doctest.DocTestSuite(cybertools.zutil.property, optionflags=flags),
         DocFileSuite('jeep.txt', optionflags=flags),
-        ))
+        doctest.DocFileSuite('rcache.txt', optionflags=flags),
+    ))
 
 if __name__ == '__main__':
     unittest.main(defaultTest='test_suite')