[postmodern-devel] Can't redefine slots as columns - why?

[Marijn Haverbeke]

Ah, you are right. If the slot object has already been instantiated as
a regular slot, I don't know of any safe, portable way to make it a
column slot. If you can think of a hack to make this work, let me
know. But for now, you'll have to solve this in some other way.

Best,
Marijn


On Tue, Mar 10, 2009 at 10:10 AM, Lucas Hope <lucas.r.hope at gmail.com> wrote:
> Hi Marijn,
>
> I stubbed out the form and the dao-circle was successfully compiled (of course).
>
> However the example circle I tried to make did not have its slot value
> set.  I understand (I think) what you were trying to do with the
> *direct-column-slot* special variable, but maybe in this case (on
> Allegro CL, btw),  while the effective-slot-definition-class works
> correctly (indicated by the correct CREATE TABLE below),  the actual
> effective-column-slot object is instantiated OUTSIDE the scope of the
> binding in compute-effective-slot-definitio which sets
> *direct-column-slot* to non-nil.
>
> There's no reason for the lisp implementation to instantiate the class
> returned by effective-column-slot immediately, as far as I can tell.
>
> (dao-table-definition 'dao-circle) ;; success!
> "CREATE TABLE dao_circle (radius REAL NOT NULL)"
>
> (setf circle (make-instance 'dao-circle :radius 5.0))
>
> (slot-boundp circle 'radius)
> => NIL ;; fail. :(
>
> -Luke
>
> On Tue, Mar 10, 2009 at 6:19 PM, Marijn Haverbeke <marijnh at gmail.com> wrote:
>> Hello Luke,
>>
>> I think (though I'm never entirely sure with this MOP stuff) that that
>> error is only there becuase I hadn't thought of the way you are trying
>> to use this metaclass, and assumed redefining a slot as a column was
>> always an accident. Could you try killing the WHEN-form on line 97 of
>> postmodern/table.lisp, doing what you're trying to do, and reporting
>> back whether it works as hoped?
>>
>> Best,
>> Marijn
>>
>>
>> On Tue, Mar 10, 2009 at 1:11 AM, Lucas Hope <lucas.r.hope at gmail.com> wrote:
>>> Hi there,
>>>
>>> I am just getting my feet wet with postmodern.  It looks like I will
>>> be doing some heavy development with it for the next couple of weeks.
>>> Wish me luck!
>>>
>>> My (first?) issue is that I want to do something similar to the
>>> following example code.  Here CIRCLE is an in-memory implementation of
>>> a circle, and it is desired to create a DAO object which moves storage
>>> to a postgres backend. (We have lots of circles...)
>>>
>>> Pretend CIRCLE has a host of useful functionality attached and I can't
>>> just point all the defmethods to DAO-CIRCLE.
>>>
>>> (defclass SHAPE () ())
>>>
>>> (defclass CIRCLE (SHAPE)
>>>  (radius))
>>>
>>> (defclass DAO-CIRCLE (CIRCLE)
>>>  ((radius :col-type real))
>>>  (:metaclass dao-class))
>>>
>>> (dao-table-definition 'dao-circle)
>>> => ERROR: Slot RADIUS in class #<DAO-CLASS DAO-CIRCLE> is both a
>>> column slot and a regular slot.
>>>
>>> Why doesn't this work, and how can I make it work?  It seems like this
>>> is useful functionality to have.  I want the DAO-CIRCLE's radius to be
>>> a column slot.
>>>
>>> Cheers,
>>>
>>> -Luke
>>>
>>> _______________________________________________
>>> postmodern-devel mailing list
>>> postmodern-devel at common-lisp.net
>>> http://common-lisp.net/cgi-bin/mailman/listinfo/postmodern-devel
>>>
>>
>> _______________________________________________
>> postmodern-devel mailing list
>> postmodern-devel at common-lisp.net
>> http://common-lisp.net/cgi-bin/mailman/listinfo/postmodern-devel
>>
>
>
>
> --
> ---------------------------------------------------
> Dr Lucas Hope - (646) 2332123 after 3pm US EST
> Machine Learning and Software Engineering Consultant
> Melbourne, Australia
>
> _______________________________________________
> postmodern-devel mailing list
> postmodern-devel at common-lisp.net
> http://common-lisp.net/cgi-bin/mailman/listinfo/postmodern-devel
>