Hi,
This time I have summoned up some ideas from web and from this group.
I use memcache to store bookmarks across page requests, this is idea
of someone else whom I cannot remember. I also stole:) the idea of
random paginating from appengine's official pagination docs.
I am very new to appengine and also web development so please comment
me on any problem with the code:
Usage:
paginate with property:
query = scComment.all().filter("game = ", game)
pgt = scPaginator(query, PAGESIZE,
order_property="create_date")
try:
comments = pgt.get_page(next_key)
except Exception, e:
logging.error("Exception occurred while retrieving
comments.["+str(e)+"]")
paginate without property: (defaults to __key__ ordering)
query = scComment.all().filter("game = ", game)
pgt = scPaginator(query, PAGESIZE)
try:
comments = pgt.get_page(next_key)
except Exception, e:
logging.error("Exception occurred while retrieving
comments.["+str(e)+"]")
here is my class:
class scPaginator:
def __init__(self, query, size, property_name=None):
self.__nextkey = None
self.__query = query # todo cannot be None
self.__pagesize = size
self.__propname = property_name
if not self.__propname:
self.__propname = "__key__" # default to __key__ ordering
then.
def get_next_key(self):
return self.__nextkey
"""
Gets the next self.__size entries from db starting from start_key
"""
def get_page(self, start_key = None, ascending=True):
entities = None
# initialize order and filter strings
if ascending:
filter_str = self.__propname + " <= "
order_str = "-" + self.__propname
else:
filter_str = self.__propname + " >= "
order_str = self.__propname
# first time?
if not start_key:
entities =
self.__query.order(order_str).fetch(self.__pagesize+1)
else:
# requesting random order?
if self.__propname == "__key__":
start_val = Key(start_key)
else:
# retrieve the entity from the passed start_key for
the filter function
# of the query object. first try memcache, then get
from db.
start_entity = memcache.get(start_key)
if not start_entity:
start_entity = db.get(start_key) # can throw
BadIndex
start_val = getattr(start_entity, self.__propname) #
can throw AttibuteError
entities =
self.__query.order(order_str).filter(filter_str,
start_val).fetch(self.__pagesize+1)
# still has next page?
if len(entities) == self.__pagesize+1:
last_entity = entities[-1]
self.__nextkey = last_entity.key()
# save the entity to memcache, because we probably will
retrieve it
# in the subsequent next page request. As many clients
will paginate the same
# offset again and again, choose a big expire time.
memcache.add(str(self.__nextkey), last_entity, 86400) #
time = 3600 * 24
del entities[-1]
return entities
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