[ZPatterns] Rack.getItem returning attributeless objects (ZPatterns newbie)

[Steve Spicklemire]

Hi Phillip,

	I would use an attribute that isn't "automatic" but requires a
successful SQL query. If your table has something like foo_id then set
the 'load by... ' attribute to that. All objects have an 'id' so your
SkinScript may not even be triggered.

-steve

Phillip Crumpler wrote:
> 
> Hi folks,
> 
> I'm having a few problems with some ZPatterns stuff at the moment and I was
> hoping someone out there could help me out with a little Zen magic...
> 
> The story so far: I have begun to develop an app based on ZPatterns - it has
> quite a few different specialists and a fair chunk of code gluing all of the
> bits together, but so far has just been dealing with objects stored within
> the Rack. Now that most of the work is done I'm trying to move all of the
> storage out to a database using skinscript.
> 
>  Things aren;t quite going as they are supposed to so I'm trying to get the
> simplest possible scenario working. The setup is Zope-2.3.3, Python 2.1,
> Zpatterns-0.4.3p1 on FreeBSD 4-STABLE - I have also tried Python 1.5.2, with
> the same results.
> 
>  I have a specialist, with the default rack, storing a zclass derived from
> DataSkin. The rack is set to 'load by accessing attribute: id'. Within the
> specialist are a few sql methods: SQL_get, SQL_change, SQL_create,
> SQL_delete. The table has two columns, id (int) and name (text). The zclass
> has a simple index_html method to show the instance's id and name
> attributes.
> 
> The rack has a skinscript method like so:
> 
> WITH SQL_get(id=self.id) COMPUTE id, name
> 
> WHEN OBJECT ADDED CALL SQL_create(id=self.id, name=self.name)
> 
> WHEN OBJECT CHANGED STORE id, name USING SQL_change(id=self.id,
> name=self.name)
> 
> WHEN OBJECT DELETED CALL SQL_delete(id=self.id)
> 
> I'm new to skinscript, so I'm not too sure about this. The only other Data
> Plug-In in the rack is a SpecialistPlugIn (but the Specialist itself has no
> Data Plug-Ins)
> 
> My (first) problem is this: a call to Rack.getItem will _always_ return an
> instance - if SQL_get returns no rows then it just ends up with no
> attributes. This means I cannot use Specialist.newItem, since:
>   Specialist.newItem
>   calls Rack.newItem
>   calls Rack.createItem
>   calls Rack.getItem , to check if the id is already used, then
>   calls Rack.retrieveItem , which instantiates a new brainless zclass and
> hands it back, which makes createItem choke, because it thinks this id is
> already taken.
> 
>  I could always just get brutal and insert it into the database directly but
> I think that would really be missing the point ;^)  How do I make
> Rack.getItem return None in this case?
> 
> Specialist.getItem works fine for ids that are in the db.
> 
> Natuarally the first person to answer will be dobbing themselves in for a
> bunch of other question, like:
> - what is the best way to use auto generated ids from the database? Override
> the Racks newKey method to get a new value from the db?
> - what are Common Instance property sheets and dataskin attribute property
> sheets, available to zclasses derived from DataSkin?
> - Have SheetProviders been implemented in ZPatterns? How are they used?
> - is there any more doco available about this sort of thing? At the moment i
> have the wiki (which is excellent) and the SkinScript syntax guide.
> 
> but that's a whole 'nother email ;^)
> 
> Cheers,
> 
> Phillip
> 
> ps: I'm subscribed to the digest, so please cc: any responses to me.
> 
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