> > I am building a grading system for students and got unexpected > > performance problems. I am using composite key for marks, which refer > > to students and subjects. > > > When I am creating a mark (for student_1 and subject_1), unnecessary > > select operations are performed (select all marks for student_1 and > > select all marks for subject_1). > > > Why these selects are generated and how to avoid them? > > The SQL issue looks like the "marks" collections on Student and > Subject issuing a lazyload for their full collection of Mark items > before the backref event appends the Mark object to each of them, i.e. > the event that occurs when you issue "mark.student = subject_1". > Ordinary collections currently don't handle being present in a > "partial" state, so in order for an append to occur, they load their > contents. > > As a workaround, you can use "lazy=dynamic" relations for the > collections, which is a special relation that can handle append > operations without the full collection being available. > "lazy=noload" would work as well but then you couldn't read from your > collections. > > A future release may look into merging some of the "dynamic" relation > behavior into an ordinary un-loaded collection so that this workaround > would not be needed. Actually this might not be a bad idea for 0.4.2, > so ive added ticket #871.
Thanks a lot for your reply! Setting the relation to be lazy="dynamic" really eliminated unnecessary selects when creating Mark. Making a default relation a bit "dynamic" is a great idea! There is problem when relation is both lazy="dynamic" and cascade="all, delete-orphan": When parent (Subject or Student) object is deleted, its children (Marks) are not deleted. When relation is not "dynamic", children are deleted correctly. Is this a proper behavior? Thanks for the attention. P.S. Congratulations to developers and users of SA with version 0.4.1! --~--~---------~--~----~------------~-------~--~----~ 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 -~----------~----~----~----~------~----~------~--~---
