> > 2. "Table per instantiable class" (aka "horizontal mapping")
> > a table for each instantiable subclass. each table has all columns,
> > including pkey and all inherited columns. There may not be anything
> > to ensure pkey uniqueness across these multiple tables.
> > pro: query by class is easy
> > con: following a foreign key to a base class (can go to any subclass) is
> > awkward
>
> RDBO supports this, since it's just a simple one-table-per class
> relationship.
Except for the "con" above.
Consider the case where at a modeling level, some class member
has a reference (foreign key) to an abstract
class (e.g. "Contact") which could refer to any of the leaf instances.
This gets awkward, to say the least -- either the foreign key
value has to be structured ("vendor:17" or "customer:19"),
or there has to be a discriminant column on the referring side.
So it seems we are back to none of them being supported
out of the box. That is not a dig at Rose; it is the embarrassing
condition of all CPAN perl OR solutions, so far as I can see.
Embarrassing, because even statically typed languages like C++ had
solutions dealing with this stuff over a decade ago.
Oh, and while I'm being grumpy, I don't see anything in the
docs about the interaction between transactions and caching --
another basic challenge in any OR architecture.
> But even that is hard to "DWIM." It'd
> have
> to be explicit:
>
> package Book;
> use base 'Product';
> Book->meta(Product->meta->clone);
> Book->add_columns(...);
> Book->initialize;
I guess I'm missing why those last 3 lines have to be explicit.
Given all the other mysto-spooko stuff going on, surely DWIM
is achievable?
-mda
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