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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