On Aug 2, 2010, at 12:41 PM, Zippy P wrote:
Hi all:
I have the following code:
class EventQuery(Query):
def histogram(self):
''' return a histogram of source / count(source) given an eventquery''
...
...
class Event(Base):
__tablename__ = 'events'
query = Session.query_property(query_cls = EventQuery)
name = Column(Unicode(128))
source = Column(BigInteger)
...
Now, Event has 54 additional attributes, some of which are quite large. In
EventQuery.histogram(), all I really need is the Event.source attribute.
'events' has over 150 million rows, and it's likely that
EventQuery.histogram() will be called for all events.
So - is there any way to 'modify' the query (self) in histogram() so that it
only returns (Event.source, func.count(Event.source)), or, for the general
case, to modify the query to return an attribute of the object? I've tried
from_self, but that seems highly inefficient (at least 20x slower than
Session.query(...) ). I'd also really like to keep histogram() as a method of
EventQuery.
I can see reasons why this would be impossible, but perhaps there's a way to
do it.
you can use values(Event.source, func.count(...)), or just put a method on
Event called histogram that uses the standard object_session(self).query(...)
approach, I'm not really sure what the using the old query_property accessor
gets you here
Thanks,
S.
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