On Monday, December 20, 2010 12:52:03 pm John Fabiani wrote:
> On Monday, December 20, 2010 12:12:12 pm marcelo nicolet wrote:
> > On 12/20/2010 05:03 PM, John Fabiani wrote:
> > > On Monday, December 20, 2010 11:49:02 am marcelo nicolet wrote:
> > >> Thank you, Ed.
> > >> In fact, I was reading about the internals of psycopg and the module
> > >> interprets python lists as postgres arrays and the other way.
> > >> The only thing I would need, then, is to "present" that list to dabo
> > >> as discrete values.
> > >> Where is the appropriate place to do that?
> > >> TIA
> > >>
> > >> On 12/20/2010 04:09 PM, Ed Leafe wrote:
> > >>> On Dec 19, 2010, at 5:39 PM, marcelo nicolet wrote:
> > >>>> But it would be nice to take advantage of the arrays this engine
> > >>>> supports. In fact, the business model of the project focuses on a
> > >>>> vector of integers, which is very inconvenient to manage in true
> > >>>> normalized form, and also as a set of scalars in the same relation.
> > >>>> So, I am asking for an example of how to integrate non standard
> > >>>> types from the backend into dabo.
> > >>>>
> > >>> I would assume that you would have to create custom handlers for
>
> these
>
> > >>> data types. I would imagine that psycopg would make the
> > >>> necessary
> > >>> conversion from the PostegreSQL datatype to the nearest Python
> > >>> type
> > >>> (list in this case). I'm not sure how Dabo would handle lists as
> > >>> column values, as I've never tried anything like that. However,
> > >>> if
> > >>> you do try and get errors at the Dabo level, please paste the
> > >>> tracebacks here so that we can see what would have to be
> > >>> improved in
> > >>> order to handle these correctly.
> > >>>
> > >>> -- Ed Leafe
> > >
> > > I have several questions
> > > Is each of the array fields fixed in the number of elements?
> > > Is each element with in the array the same data type?
> > > Are you going to search on any of the elements?
> > > Will you be adding elements to the array?
> > >
> > >
> > > Johnf
> >
> > Yes, they are of fixed size; all elements are integers (in this case, of
> > course). The arrays will not change in size once stored.
> > Regarding query, the arrays will be retrieved always in their entirety;
> > if the user request some filtering, it will be done programatically, not
> > at the backend level.
>
> Untested and just things I'd try first:
> First I believe the dbPostgres.py will return '?' as the datatype but the
> field name should be there. So it might be possible to use the standard
> createBizobj() routine to create the bizobj. Therefore, you could use a
> virtual field routine to populate the added fields. Of course you then
> need to handle the save (I think you will no matter what you do).
>
> Something like;
> self.VirtualFields = {'listitem1':self.getItem_1,
> 'listitem2':self.getitem_2, ...}
>
> def getitem_1(self):
> listitems = self.Record.fieldname
> return listitems[0]
>
> A second way would be to create a DataSource (manual define). The write
> the method to retrieve the data and populate the DataSource/DataSet.
>
> Once the data is in a bizobj it should lend it self to all the filtering
> required.
>
> Then over write the bizob's save routine to populate the array. Rebuild
> the list and pass it to psycopg.
>
> I try my hardest to always get everything into a DataSource first. That
> way I can work within the Dabo framework and use all the tools.
>
> I will not say I haven't gone way outside of Dabo to get the job done
> because I have. But I call that the 'dark side' and it's always better to
> work with the force Luke!
>
> Johnf
Oh I forgot some important thoughts:
You can always use the Postgres functions to return the array as needed. I've
had to do this several times in the past. Returning 'SETOF ' or maybe you
could create a view that expanded the array. This also makes creating the
bizobj very easy. And don't forget you can use 'Rules' to allow inserts,
updates, and deletes for views. Like I said using views this makes using Dabo
much easier!
Johnf
_______________________________________________
Post Messages to: [email protected]
Subscription Maintenance: http://leafe.com/mailman/listinfo/dabo-users
Searchable Archives: http://leafe.com/archives/search/dabo-users
This message:
http://leafe.com/archives/byMID/[email protected]
