On Feb 18, 2008, at 10:34 AM, Julien Cigar wrote:

>
> My question is: can I have a select() object which return a scalar for
> the polymorphic_identity parameters ? I guess it should be possible to
> put anything else than the FK value ?
>

theres no reason you cant map to select([content,  
content_type.c.name]).select_from(content.join(content_type)) .   If  
you take that select and outerjoin it to both the "news" and  
"science_news" tables, you can stick it just under mapper(...,  
select_table=<select>) and keep the base tables simple.   The caveat  
here is that you have to set either "content_type_id" or  
"content_type" (if the latter, by using a relation()) on each object  
manually.

another option would be to just grab the integer "content_type_ids"  
really quick before configuring the mappers, and use the integer  
values directly for the "polymorphic_identity" field.

we will eventually also be implementing a user-defineable callable for  
"polymorphic_on" too which could combine both approaches.

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