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

[Lucas Hope]

Hi Marijn,

I guess I suffered from working 12 hours and then emailing you.

My little example had a fatal flaw: I hadn't defined an :initarg for
radius!  Some preliminary (re-)testing indicates that your initial
fix/alteration works.

Thanks for your help!

-Luke


On Tue, Mar 10, 2009 at 9:51 PM, Marijn Haverbeke <marijnh at gmail.com> wrote:
> 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