Re: [SQLObject] RFP: SQLObject-Web ?

[Stef T. <st...@um...>]

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Oleg Broytmann wrote:
> On Mon, Feb 02, 2009 at 09:39:06PM -0500, Stef Telford wrote:
>> Oleg Broytmann wrote:
>>> On Mon, Feb 02, 2009 at 03:07:49PM -0500, Stef Telford wrote:
>>>> alias's will stay 'fixed' at webserver/framework launch .. no
>>>> ?
>>> Alias counter is increased on every instantiation of Alias().
>> Stupid question here .. but .. why ? (sorry, I know that this
>> could be a large answer but..)
>
> Because SQLObject needs to generate unique alias names and a global
>  counter is the simplest way to do it. Think about joining a table
> with itself - you need two different names for the table.
>

Thanks for your time once again Oleg. but.

Sorry, perhaps I am being stupid here (always a possability) but, how
many self joins are we expecting in a query ? I mean to say, isn't
saying 'selfName = self.__class__.__name__ + "_%d" % int(random())'
good enough ? I don't know about how mySQL planner would deal with a
self join on a self join .. but I can guess (eg; NOT well) so ..
surely we only need to worry about -1- self join per table in any
query ? and since queries are always 'stand alone' we don't have to
worry about leakage to other areas/queries, why not merely chose a
random number and append ?

Sorry, I guess I am not grasping the fine details here.. my apologies :)

>> Also, whilst I am here, a couple more stupid questions, is there
>> any flag in the SQLObject which tells me if the object was
>> 'created' from the database or instantiated from the
>> database/cache ? I ask only because it would be -awfully- handy
>> to have .. I did look at _creating but, that's not the right item
>> (obviously)
>
> There is no and I really fail to see a difference. Why do you want
> to distinguish them?
>

Really ? Well, in my application, there is a lot of 'house keeping'
that needs to be done after a new row is created in the database, and
it seems crazy to call _setattr_ if the row has been grabbed from the
cache (as any call to setattr would/should invalidate the object in
the cache and force a reload from the database).

Think of 'completeName' .. which is simply self.firstName + " " +
self.lastName. I can think of a 'good reason' to only call -that-
after the initial object has been created (I know that this should be
a model function which jst returns the firstName + " " + lastName but,
go with me here, I am trying to keep my example simple).

If there is a 'newRowInDB' flag, then I can say something like;
> def _init(self, id, connection=None, selectResults=None): '''
> Overload this method if you need to do anything special '''
> SQLObject._init(self, id, connection, selectResults) if
> self.newRowInDB: self.completeName = self.firstName + " " +
> self.lastName memcache.put("%s_%s" % (self.__class__.__name__,
> self.id))

If we -dont- have that newRowInDB flag, then any cache hit will call
the _setattr_ on completeName, which will thus (potentially)
invalidate the object in the cache and cause another get for SQLObject
.. which will cause _setattr_ to be called... round and round we go.

I think even having a flag set on self somewhere inside the
_SO_finishCreate would do the trick, but, I am assuming that this is
the only place that creates new objects in the db.

>> Lastly (I promise) I am thinking of over-riding the
>> _SO_finishCreate in the SQLObject subclass so that all database
>> inserts go to the master rather than any slave. I would also have
>> to override _SO_setValue and set (of course) .. any other methods
>> in SQLObject that would have to be subclassed ?
>
> No, these seem to be enough.
>
Danke.

Regards
Stef
> Oleg.

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