One feature that caught my attention when I first started using
sqlalchemy was this example:
l = User.mapper.select_by(street='123 Green Street')
This is in the section entitled 'Useful Feature: Creating Joins via
select_by' and it touches on something I think is severely needed. If
you're going to go to all the trouble to define relationships in your
model, why should you need to redefine them when you query the data. As
far as I can tell, this doesn't work past the first relation ship (am I
wrong?), but is there a reason it can't?
I'll give an example. I work with drinking water samples. The
relationship between a Water System and Sample Result looks like this:
Water System -> Facility -> Sampling Point -> Sample -> Result
So say I want to know which water systems had high lead levels sampled
after January.
This should be possible like so:
high_systems = WaterSystem.select_by(Sample.c.date_collected >
'2006-01-01',
Result.value > max_value)
I'm not saying this is the correct syntax. What I am saying is that
sqlalchemy already knows how these tables are related to each other, so
I should not have to create an explicit join for the query.
What do you think? Are there technical reasons this can't work?
Randall
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