Just a note that there is a db.ComputedProperty included in the SDK.
http://code.google.com/p/googleappengine/source/browse/trunk/python/google/appengine/ext/db/__init__.py#3339
Works just like DerivedProperty.
Robert
On Wed, Mar 2, 2011 at 07:29, Nickolas Daskalou <n...@daskalou.com> wrote:
> +1. Nick Johnson's DerivedProperty has proved invaluable during the course
> of my development on App Engine.
> Jon, in your example, this is how you could implement it using
> DerivedProperty:
> ----------------------
> from aetycoon import DerivedProperty
> class Message(db.Model):
> text= db.StringProperty(required=True) # text of the message
> likes= db.StringListProperty() #usernames that liked the message
> @DerivedProperty
> def num_likes(self):
> return self.likes and len(likes) or 0
> ----------------------
> Then to get the top 10 liked messages:
> ----------------------
> messages = Message.all().order('-num_likes').fetch(10)
> ----------------------
> Nick
>
>
> On 2 March 2011 22:59, djidjadji <djidja...@gmail.com> wrote:
>>
>> You can use the DerivedProperty from the aetycoon lib written by Nick
>> Johnson (search his blog).
>> During a put it will update the property no need to perform the count
>> yourself.
>>
>> 2011/3/1 ogterran <jonathanh...@gmail.com>:
>> > Thanks guys. I'll add another IntegerProperty to increment the count
>>
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