On 3/23/06, Michael Bayer <[EMAIL PROTECTED]> wrote:
> so you only have a Select, you dont
> have the Class or Mapper?
> does that mean you want to inspect
> the Select to see what Table it refers to,
> figure out what Mapper talks to that Table ?
> youre free to do anything like that, you can
> pull out the "where" clause from the select
> and send it to the mapper, etc.
I have Class and Mapper. I *want* to use Class or Mapper.
Even subject says: "deferring mapper selects". The thing
is that it executes and fetches immediately.
The reason I mentioned Select in my examples was because
that was the only thing that I could make work in stages.
I also thought that some kind of "select" could be returned
by Class - something that can be used to postpone
execute/fetch and to modify query.
Never mind. In my program I'm already using Class to
select based on pager.limit and pager.offset. I wanted
to make it the other way because it is a better way.
It would make it possible to perform pagination later
without my business objectes ever needing to clutter
thair interface with pagination. Things would also be
efficient because only 10 rows would be fetched at any
time.
Incidentally, that is the way I saw other people doing
with SQLObject. SQLObject returns some kind of proxy
which fetches only when you acces the result. This
"access" can be slice operation which is than used
to perform LIMIT/OFFSET modification of underlying query.
Very Powerful:
results = SOCampaign.select(...)
campaigns = results[a:b] # Now it performs LIMIT-ed execute/fetch
> although, I am not sure about that design ?
> if youre dealing with objects you should be
> passing around the class and a set of criterion,
> not a raw Select object, no ?
I almost agree. I also want to use Classes and stuff,
but I don't want to expose my where conditions inside
controller or event worse - use LIMIT inside my business
objects (I also have to COUNT inside business objects).
I just want to be able to say:
# don't want to care about complex WHERE at this point
leads = campaign_obj.best_leads(min_weight=min_weight)
# and while displaying my "Best Leads" page use...
pleads = Pager(leads, 'leads') # ... to get only 10 that need to be displayed
Currently I must do this:
nav = navigation.Nav(navtxt)
leads, nav.total = campaign_obj.best_leads(min_weight=min_weight,
**nav.limit_offset)
and I hate it. All my business functions are constantly
COUNTing and littering their interface with LIMIT/OFFSET
noise.
> not sure if this is interesting, but you can
> also create the unexecuted Select object from
> the mapper:
>
> s = mapper._compile(Campaign.c.id==7)
>
> if you look at what _compile does, youd see why
> its a risky endeavor to use it if the mapper has
> any kind of eager loading, esp. with limits and
> offsets.
I guess that I'm not gonna use it then.
I could make something like this:
class ResultProxy(object):
def __init__(self, obj):
self._obj = obj
self._executed = False
self._results = []
def _check(self, key=None):
if not self._executed:
if isinstance(key, slice):
# fiddle with limit and offset
self._obj._kw['limit'] = ....
self._results = self._obj.select(*self._obj._arg, **self._obj._kw)
self._executed = True
def __getitem__(self, key)
self._check(key)
if isinstance(key, slice):
return self._results
else:
return self._results[key]
def __len__(self):
self._check()
return len(self._results)
def __...__(self):
self._check()
return ...
class PagerSupport(object):
def pselect(self, *arg, **kw):
self._arg = arg
self._kw = kw
return ResultProxy(self)
class SACampaign(PagerSupport):
pass
This is something I wrote inside this mail so it
is obviously untested and with many bugs and
wrong design decisions, but it is here just to
give you a general idea.
The thing is that I *don't* like it:
- I have to subclass
- I have to use special "pselect" functions
- I have to write ResultProxy class
- I have to use SA results in nonobvious way
(it may be obvious for SO but not for SA)
- I cannot give Pager to others because it
is too coupled
It would be better if it was part of the framework.
It seems almost there because you can do it
with Select. Or should I say: I guess you can
do it. I didn't understand if it would work or not
when you mentioned eager loading...
Regards,
Tvrtko
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