On Nov 20, 2007 5:23 PM, Michael Bayer <[EMAIL PROTECTED]> wrote: > On Nov 20, 2007, at 4:37 AM, Gaetan de Menten wrote:
> > I have some classes with "standard python" properties which target > > another python object and also uses several columns in the database. I > > also got a global factory function to create an instance of that > > target object out of the value of the columns (the class of that > > target object can vary). > > > > Now, I'd like to use those properties in filter criteria, as so: > > > > session.query(MyClass).filter(MyClass.my_prop == value)... > > session.query(MyClass).filter_by(my_prop_name=value)... > > > > I've tried using composite properties for that (passing the factory > > function instead of a composite class), and it actually works, but I'm > > a little nervous about it: can I have some bad side effect provided > > that in *some* cases (but not always) the target object is loaded from > > the database. > > > > > > > I also dislike the fact I have to provide a __composite_values__ on > > all the possible target classes, while in my case, I would prefer to > > put that logic on the property side. I'd prefer if I could provide a > > callable which'd take an instance and output the tuple of values, > > instead of the method. Would that be considered a valid use case for > > composite properties or am I abusing the system? > > im not totally understanding the "all possible target classes" concept > here, you're creating classes on the fly ? No, but my property returns object of different classes. Let's call it a polymorphic property. > if you are in fact > creating new classes on the fly, i dont see whats so hard about > tacking on a __composite_values__ to each one as well (i.e. dont you > have a single function that is doing the generation ?) > I dont > understand what "put that logic on the property side" means > otherwise. It means that my property is handled by a class and I'd rather put the __composite_values__ function in that class, than in my several target classes (some of them have nothing to do with the database, so it seems awkward to add a method for that). > If you can show me some example code that might help, but > I think you probably are abusing the system here and the > MapperProperty idea that Chris mentioned is probably the way to go. Yeah, that seemed like an elegant way. > > I've also tried to simply change those properties to descriptors so > > that I can override __eq__ on the object returned by accessing the > > property on the class. This worked fine for "filter". But I also want > > to be able to use filter_by. So, I'd wish that > > query(Class).filter_by(name=value) would be somehow equal to > > query(Class).filter(Class.name == value), but it's not. filter_by only > > accepts MapperProperties and not my custom property. > > > > Well the general case of filter_by() and filter() awareness is > accomplished via synonym(). the filter() part for synonym() doesnt > work yet but we have ticket #801 to address that. this ticket will > take the existing Python property and put an InstrumentedAttribute > wrapper around it. > > But in this case you aren't making synonym(), you pretty much want a > synonym() that doesn't target any particular column. Indeed. > Maybe we could > expand ticket #801 to include that, or maybe make some new ticket for > this. We'd just have another mapper function thats like synonym() but > doesnt actually target a column, it just adds that name to the list of > properties. But also, the target property, or something else, would > have to provide the MapperProperty interface it as well, like Chris > says. So a new kind of MapperPropery would be needed here. Done in ticket #875. Thanks for your reply. -- Gaëtan de Menten http://openhex.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 [EMAIL PROTECTED] For more options, visit this group at http://groups.google.com/group/sqlalchemy?hl=en -~----------~----~----~----~------~----~------~--~---
