have you tried using query + join() + contains_eager() ? any query you like can be used to build the object graph of your choice along relations().
bojanb wrote: > > Here's something I've been struggling with recently. I'll include the > description of steps that got me here, as I believe the context will > make the question clearer. > > It all started because I needed to show data (eg. in a list form) from > two related tables (classes). However, SQLAlchemy would emit one SQL > query for getting the objects of the first class, then one query each > for each access to attributes of the other class. It obviously loads > the attributes lazily, which is fine most of the time but grossly > inefficient in this case (as there can be thousands of records in the > first table). > > "Aha, I'll use eagerload!" I thought. Alas, it doesn't seem to work > for inherited classes. A message in this group suggests that it > doesn't work for self-referential inherited classes, but in this case > it didn't work for plain inherited classes that don't contain > references to self. I'll write a test case that shows this later. > > OK, I then decided to create a new class mapped against the two > tables, using join() in a mapper. This worked great regarding the > emitted SQL - session.query on new object generates the correct SQL > even with the (deep) inheritance tree that we have. Modifying the > attributes on of this object also writes them to correct respective > tables on commit. Great! The new class even conceptually fits nicely > with the rest of the application (e.g. I realized it's more of a > business object while the two underlying classes/tables are more of an > implementation detail; I'm not sure I even need the other two classes, > just the tables may be enough). Fantastic! > > However, I can't figure how to create new instances of this (composite > as I call it) class. Since it contains fields both for autogenerated > primary key from the first class and foreign key from the second > class, I cannot set the foreign key because I don't know the primary > key before I commit, and commit fails because the foreign key is still > null. > > Am I just missing something or am I attempting a no-no? I would think > that since I've defined the attributes to be identical in the > "oncluase", SQLAlchemy would now that the two are dependent and would > not complain about the null value. > > Of course, I can always create the two other objects, but being able > to do it this way fits much more nicely with the rest of the > application. > > > --~--~---------~--~----~------------~-------~--~----~ 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 -~----------~----~----~----~------~----~------~--~---
