johann sorel ha scritto:
> Hello,
> 
> Until today I was using Expression only with Features.
> I'm wondering how it works if I need to using it on something different.
> 
> Let's say I a have a mathematic operation which return me a double value 
> : MyVar
> 
> I would like to use an expression like  2 * MyVar + 15 :
> How do I give the MyVar value to the expression to evaluate it ?

The model uses a PropertyAccessor to go from the property name to
the value. So you need to pass in an object (it may be a simple
hashmap for example) that contains all the properties you might
want to use, and then build a property accessor that can grab
MyVar value out of it.
In particular, you'll have to code a PropertyAccessorFactory,
a PropertyAccessor, and register them in the SPI.
Have a lok at SimpleFeaturePropertyAccessor/Factory for
an inspiration.

Hope this helps
Cheers
Andrea

-- 
Andrea Aime
OpenGeo - http://opengeo.org
Expert service straight from the developers.

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