Ed -
its interesting....though I wonder if theres a way the service could be
moved out of a specific "Inventory" object and out somehere more
generically...like "if not selectcache.execute('foo'):" etc. (with some
threadlocal logic to keep it sane). Id say put it on the Wiki as its own
page and link it on the "UsageRecipies" page for now.
- mike
Ed Suominen wrote:
> I've refined my convenience method for select() and made quite a bit of
> use of it at this point. An updated zoo.py example is at
> http://edsuom.pastebin.com/552888.
>
> The method looks like this:
>
>> def select(self, *args, **kw):
>> """
>> When called with a single argument, I{name}, this method indicates
>> if
>> the named select object already exists and sets its context to
>> I{name}.
>>
>> With multiple arguments, the method acts like a call to
>> C{sqlalchemy.select(...).compile()}, except that nothing is
>> returned. Instead, the resulting select object is stored in the
>> current context.
>>
>> With no arguments, the method returns the select object for the
>> current context.
>>
>> """
>> if len(args) == 1:
>> context = args[0]
>> self._context = context
>> return self._selects.has_key(context)
>> else:
>> context = getattr(self, '_context', None)
>> if len(args) == 0:
>> return self._selects.get(context)
>> else:
>> self._selects[context] = select(*args, **kw).compile()
>
> Just before a block of code that will use a given select() object (let's
> call it "foo" in the great programming tradition), insert a conditional
> block:
>
> if not self.select('foo'):
> self.select(
> [fromStuff],
> whereStuff)
>
> The first call to self.select() indicates whether the select object
> "foo" has already been created. It also sets the context to "foo" for
> other calls to self.select(). The second line, which runs only if
> needed, creates the table "foo."
>
> Then you can simply do self.select().execute(...) and your code will use
> the cached "foo" select object. Bindparams are very useful in the select
> constructor, allowing you to compile and cache everything about the
> select() instance that is fixed and use it with only the custom
> parameters that need to be custom.
>
> Comments and critiques welcome -- I'm a new but very impressed
> sqlalchemy user.
>
> - Ed Suominen
>
>
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