how do you do a count of a result set?

[Brian Quinlan]

On 10 Jul 2010, at 16:21, John Nagle wrote:

> On 7/9/2010 11:08 PM, Dennis Lee Bieber wrote:
>> On Sat, 10 Jul 2010 06:56:13 +0200, Rene Veerman<rene7705 at gmail.com>
>> declaimed the following in gmane.comp.python.general:
>>
>>> hi.
>>>
>>> i'm using this function;
>>>
>>>
>>> 	def dbCacheGet(self, appParams):
>>> 		results = db.GqlQuery(
>>> 			"SELECT * "
>>>             "FROM DBcache "
>>>             "WHERE url='"+appParams['urlCalled']+"'"
>>> 		).fetch(1)
>>> 		if results.count('*')==0:
>>> 			return None
>>> 		else:
>>> 			return results
>>> 		
>>>
>>> i dont think this will work correctly.
>>> i need a function that returns the complete count in the results  
>>> variable.
>
>   This is really a Google AppEngine question.  Ask in their support
> forums.

http://groups.google.com/group/google-appengine-python would be a good  
place to start.

>   It's worth noting that for many database queries, asking how many
> hits there are can cost almost as much as actually retrieving them.

That is the case with the App Engine datastore. If your counts contain  
more than a few hundred results then you would be better so store them  
somewhere.

Cheers,
Brian