Re: Vertical inheritance for PyDO2.1?

On Thu, Aug 04, 2005 at 11:48:59AM +1000, Adam Ward wrote:
> Jacob,
> 
> I would like to see PyDO 2.1 support vertical inheritance.

OK.  In what way?

If you want a single PyDO object that actually maps to more than one
table, so that selects perform a join and updates, deletes, etc., do
potentially multiple operations, then it would be possible to write a
facade class that delegates to various joinable table-specific PyDO
objects and presents a PyDO-like api.  Is this the kind of thing you
have in mind?  This wouldn't require any changes to pydo.PyDO itself,
I believe; and wouldn't be connected at all to Python inheritance.  I
think a facade pattern would be the way to go; retrofitting this sort
of behavior into pydo.PyDO itself seems impractical at this stage.

Whether or not that is what you had in mind, it isn't a bad idea, I
think, and would also a pretty general facility applicable beyond
vertical inheritance relationships for creating business objects that
are less closely tied to a single specific db table.  You could create
views in Python, in effect; you could perform distributed transactions
across databases; it would (hopefully) be less work to create an
object layer that is less directly tied to the database layer.  Of
course, you can (and probably often should) do this now; the question
is, what tasks in so doing need to be automated?  Mapping underlying
fields to the business object's attributes is one.  Generating sql for
common cases, as with PyDO objects, is another, for mutations and find
operations.  These are, in principle, straightforward.  What else
would you want such an object framework to automate, and what hooks
would you want it to have?  And when will it be ready? :)

Or have I read your mind inaccurately, and do you mean something
entirely different?

> Do you have any plans for other inheritance models (other than flat) for
> this release?

Not currently.  

Cheers,

js

PS.  I am so glad that mutt leaves temp files around so promiscuously;
I just now accidentally hosed my terminal as I was about to send this,
but was able to rescue it out of /tmp! 

-- 
Jacob Smullyan

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