On Dec 12, 2007 6:20 AM, King Simon-NFHD78 <[EMAIL PROTECTED]> wrote: > > Felix Schwarz wrote: > > Hi, > > > > after reading the docs [1] I thought that something like > > session.query(User).filter(User.c.id > 3)[0] > > should work even if the filter clause does not return any rows. > > > > But - compliant with Python's behavior - SQLAlchemy raises an > > IndexError. > > (...) > > File > > "/usr/lib/python2.4/site-packages/sqlalchemy/orm/query.py", > > line 577, in __getitem__ > > return list(self[item:item+1])[0] > > IndexError: list index out of range > > I expected that [0] applied to query without results would > > return None. > > > > Did I miss another possibility for LIMIT'ing queries (using > > sqlalchemy.orm)? > > > > fs > > > > [1] > > http://www.sqlalchemy.org/docs/04/ormtutorial.html#datamapping > > _querying > > I think being matching Python's behaviour is definitely the right way to > go. If you want to get None specifically for index [0], you can use the > 'first' method on query. > > If you are happy get an empty list, you could use a slice and then call > .all()
The issue is that [0] in Python superficially looks like [A:B] but is in fact something different. [A:B] was added to SQLAlchemy to represent .offset(A).limit(B-A). [0] came along for the ride but has incompatible semantics when the record does not exist. I guess I would favor None because [N]'s closest equivalent is .fetchone() which does that, and if they really wanted [] they should have done [:1]. Raising IndexError is the native Python equivalent, but the whole concept of operator overloading is that we do what makes sense for the object. A query is not a list. If we define [N] as "skip N-1 records and do .fetchone()", that's defensible. The only people who will be bothered are existing programs that are expecting IndexError. Are there that many of those, given that I don't think [N] is even documented? -- Mike Orr <[EMAIL PROTECTED]> --~--~---------~--~----~------------~-------~--~----~ 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 -~----------~----~----~----~------~----~------~--~---
