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Just a quick comment on this --- Ian may have a better idea.<BR>
<BR>
Yes, if we offered a nice clean place to put all of those, it would make it obvious<BR>
where to put validation. (I will certainly think about that in the future.)<BR>
<BR>
Here is a technique that I use, that is very effective for me, but not generally <BR>
applicable: I use DCM, which is in the contrib directory and basically provides<BR>
wrappers for the create/read/update/destory operations, similar to those you <BR>
name below. I use :after methods on these operations (specialized on Director<BR>
classes, since it is generally class dependedent) to send objects to a text indexer<BR>
in a background thread whenever they change. (I was using Lucene-ws but now<BR>
use montezuma; it makes sense to do these operations in a back-ground thread since<BR>
a web-service call might block the thread that needs to get a response on to the <BR>
glass as fast as possible.)<BR>
<BR>
This is an extraordinarily powerful and elegant feature of LISP. If you have a method<BR>
that gives you a "change point" (I believe that is what you are asking for) then you can<BR>
easily put a :before method in a completely different file that performs validation and<BR>
signals an exception or takes some other action that interrupts the intended operation. <BR>
One of the beauties of this is that the validation rules can be easily kept quite separate from the rest of the code.<BR>
<BR>
I suppose this same technique could be applied even if you do not have clearly defined<BR>
methods; but personally I consider this clarity to be one of the advantages of the DCM code.<BR>
Of course, one can more or less easily create your own validation points, without becoming<BR>
dependeing on the DCM code. <BR>
<BR>
Here's my example code:<BR>
(defmethod register-obj :after ((dir indexing-director) (mo managed-object))<BR>
(pub-and-proc (list "indexdocument" dir (k (mid mo))))<BR>
)<BR>
<BR>
(defmethod delete-obj :before ((dir indexing-director) (id key))<BR>
(pub-and-proc (list "removedocument" dir (k id)))<BR>
)<BR>
"register-obj" and "delete-obj" are defined in DCM.<BR>
<BR>
<BR>
On Fri, 2006-08-11 at 17:17 -0400, Daniel Salama wrote:
<BLOCKQUOTE TYPE=CITE>
<PRE>
<FONT COLOR="#000000">Hi,</FONT>
<FONT COLOR="#000000">This may be more of a suggestion since I think I already know the </FONT>
<FONT COLOR="#000000">answer.</FONT>
<FONT COLOR="#000000">I come from the Ruby On Rails world and, as some of you may know, </FONT>
<FONT COLOR="#000000">their Active Record module provides hooks that allow the automatic </FONT>
<FONT COLOR="#000000">and customized evaluation of validation rules at different stages of </FONT>
<FONT COLOR="#000000">the committing process.</FONT>
<FONT COLOR="#000000">At first, I was going to as how can I hook validation rules into the </FONT>
<FONT COLOR="#000000">persistent machinery. I guess I could (should) always wrap my commits </FONT>
<FONT COLOR="#000000">in transactions and then I could perform the validation process </FONT>
<FONT COLOR="#000000">within the transaction and, therefore, I could commit or abort </FONT>
<FONT COLOR="#000000">depending on the validation results.</FONT>
<FONT COLOR="#000000">However, as my Lisp knowledge is still limited, I'd like to suggest </FONT>
<FONT COLOR="#000000">for some future version of Elephant, the inclusion of some type of </FONT>
<FONT COLOR="#000000">macro that works somehow like a with-transaction type operation. This </FONT>
<FONT COLOR="#000000">macro could support generic methods that could be "customized" per </FONT>
<FONT COLOR="#000000">class just like CLOS generic methods to support model validation. </FONT>
<FONT COLOR="#000000">Just for reference, Rails validation hooks support, among others:</FONT>
<FONT COLOR="#000000">- before validation</FONT>
<FONT COLOR="#000000">- after validation</FONT>
<FONT COLOR="#000000">- before create</FONT>
<FONT COLOR="#000000">- after create</FONT>
<FONT COLOR="#000000">- before save</FONT>
<FONT COLOR="#000000">- after save</FONT>
<FONT COLOR="#000000">- before destroy</FONT>
<FONT COLOR="#000000">- after destroy</FONT>
<FONT COLOR="#000000">Maybe some of this functionality could be implemented in the near </FONT>
<FONT COLOR="#000000">future. Maybe it's not that big of a deal, but, since my Lisp </FONT>
<FONT COLOR="#000000">knowledge is limited, I am just throwing this suggestion.</FONT>
<FONT COLOR="#000000">Then again, maybe there is a better way to do it and I just have too </FONT>
<FONT COLOR="#000000">much of a Rails mentality for the time being :)</FONT>
<FONT COLOR="#000000">Thanks,</FONT>
<FONT COLOR="#000000">Daniel</FONT>
<FONT COLOR="#000000">_______________________________________________</FONT>
<FONT COLOR="#000000">elephant-devel site list</FONT>
<FONT COLOR="#000000"><A HREF="mailto:elephant-devel@common-lisp.net">elephant-devel@common-lisp.net</A></FONT>
<FONT COLOR="#000000"><A HREF="http://common-lisp.net/mailman/listinfo/elephant-devel">http://common-lisp.net/mailman/listinfo/elephant-devel</A></FONT>
</PRE>
</BLOCKQUOTE>
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