On Thu, Oct 9, 2008 at 9:01 PM, John Hunter <[EMAIL PROTECTED]> wrote:
>> if the attribute is "attached" to either PriceData or FundamentalData, >> the general route towards this kind of thing is to use >> column_property(). You can place subqueries which correlate to the >> base table in those. If you're looking for a third mapped object >> along the lines of RatioData, you can map such a class to a select() >> object which represents the query, although this seems more like an >> attribute on PriceData. >> >> the column_property() is usable in queries and you can also customize >> how it compares using a user-defined PropComparator. >> >> a brief example is at: >> http://www.sqlalchemy.org/docs/05/mappers.html#advdatamapping_mapper_expressions Here's another question: I have to compute several of these price/something ratios. For performance, it seems like it would be best to do them all in a single select, eg price_sales , price_income= orm.column_property( sa.select( [price/FundamentalData.sales, price/FundamentalData.income], (ticker==FundamentalData.ticker) & (date>=FundamentalData.reportdate), ).order_by(FundamentalData.reportdate.desc()).limit(1)) but doesn't appear to be allowed, InvalidRequestError: Scalar select can only be created from a Select object that has exactly one column expression. WARNING: Failure executing file: <sqlalchemy_demo.py> Is there a way to do several of these at once? Thanks again, JDH --~--~---------~--~----~------------~-------~--~----~ 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 -~----------~----~----~----~------~----~------~--~---
