On Mon, Dec 5, 2011 at 11:30 PM, Michael Bayer <mike...@zzzcomputing.com> wrote: > On Dec 5, 2011, at 1:39 PM, Daniel Nouri wrote: >> Thanks for your explanation. I haven't used hybrid a lot yet and this >> helped me understand what it does and what not. >> >> Your last example that uses a 'with_transformation', i.e. a protocol >> that I guess would amount to allowing to run the query through an >> arbitrary function, is quite nice to read, and I'd definitely be a >> user. Then again, there's nice enough alternatives for what I'm >> trying to do, so I'll be fine without. :-) > > OK, well with_transformation is literally: > > def with_transformation(self, fn): > return fn(self) > > so there's not much controversy there. I've added it and wrote up an example > of how to combine this with a hybrid comparator, to produce two approaches > for your problem (which just makes a nice example). It looks *interesting*, > but I don't know how much this pattern would catch on - if it's one of those > patterns that can keep expanding out or not. Check it out at: > > http://www.sqlalchemy.org/docs/orm/extensions/hybrid.html#building-transformers
Awesome! Thanks for not only giving me a way to do this, but basically solve my homework too. :-) I have to admit I only understood Comparators now. And why the need for a 'with_transformation' on top of the Comparators. The way GrandparentTransformer's functionality is put together using 'with_transform' seems very elegant. The GrandparentTransformer in the second example that separates 'join' from 'filter' seems interesting and the implementation slightly easier, but the query part is definitely harder in a way that exposes maybe a lot of what's going on behind the scenes. I imagine that novice users would also be tempted to think that they can do "query.filter(Node.grandparent == Node(id=5))". Since the "join" in your example doesn't affect the way that subsequent filters work, I guess it's not useful for the user (doing the query) to know if it's a transform or a filter, right? (I don't pretend I understand the full scope of this, so wouldn't be surprised if this were a choice of explicit over implicit or some such.) -- http://danielnouri.org -- You received this message because you are subscribed to the Google Groups "sqlalchemy" group. To post to this group, send email to sqlalchemy@googlegroups.com. To unsubscribe from this group, send email to sqlalchemy+unsubscr...@googlegroups.com. For more options, visit this group at http://groups.google.com/group/sqlalchemy?hl=en.
