Am Dienstag, 9. Januar 2007 17:01 schrieb Michael Bayer:
> we do have an extension called "associationproxy" that is used for
> something similar with association objects...it may give you some
> ideas on how to proxy attributes across. i dont think you should
> approach the idea of "adding individual properties" as "quite
> complicated"...for example, you could write a function that adds all
> the "Address" properties to the "Person" class en-masse:
>
> for key in class_mapper(Address).props:
> setattr(Person, key, property(...some getter function...))
>
> if you come up with something generally useful in that idiom, you can
> post to the SA wiki or we can even make another extension if its
> really of general use.
At first, thanks for your quick answer.
My basic idea was to maintain the abstraction between the data model and the
actual object. So the ideal place to specify such things would be in the
mapper. To my mind, some "magic" with the properties could do it, e.g. like
this:
mapper(Person, person_table, properties = dict(
address=relation(Address, secondary=r_pers_addrid_table,
proxy_relation_attributes=True))
In case "proxy_relation_attributes" is set to "True", all columns (except the
foreign keys which are obsolete) are made accessible through the relation -
very simple syntax.
Correct me if I'm wrong, but many to many relations are normally done this
way:
table1 <---> association_table <---> table2
table1 has a one to many relation to association_table and table2 has also a
one to many relation to association_table. From the perpective of table1, it
should therefore in any case be possible to locate association/relation
attributes along with the attributes of table2 (and the same in the other
direction). The only problem could be name clashes, which could probably be
handled in some way (e.g. raise an exception or prefix them).
This may also obsolete the "associationproxy" - but maybe I don't fully
understand its concepts.
This solution would make it possible to alter the data model, e.g. make a one
to many relation from a many to many relation, e.g.:
table1 <-----> table2
without having to touch the object representing the function - the only thing
I'd have to change is the mapper.
I have no clue how I would implement such a relation property as I'm very new
to SA, perhaps it's impossible for some reason. However, I think putting
attributes in association tables is a common pattern in data models, so this
could be of use for many SA users.
What do you think of this idea?
Best Regards,
Hermann
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