On 23.04.2010, at 17:03, Michael Bayer wrote:
On Apr 23, 2010, at 9:59 AM, Paul Balomiri <paulbalom...@gmail.com>
wrote:
Hi,
Thanks, for your reply. I was aware that it is not just a string
substitution,
and that the bindparams also maps the type of the parameters e.t.c.
But is it possible to supply a type /set of types which are or
represent a lexical sub-structure ?
I might go into doing it, but first i want to check that i'm not
reinventing the wheel.
I noticed that the where clause can be supplied several times, so
select( [my_table_metadata]). where(....). where(...) is valid,
thus it is possible
for this special case to insert a logical expression after the
initial select() definition.
I am looking for a similar, but more general case, not necessarily
using bindparam where func.now()
would be a valid substitution or insertion element into a
preexisting expression.
Why not just create a python function that generatively produces the
desired statement based on arguments? I don't see the advantage to
something more magical than that.
Well, this is what i already do:
lazy_sql_partial = functools.partial(lambda x: select([...] ,
from_obj(func.a(bindparam('a'),bindparam('b'),x ))) )
and then i name the binding like so:
lazy_sql_unbound = (lazy_sql_partial, ("funcarg"))
At the time when i generate the sql expression I do not know the
parameters, not even a default. Those are generated based on user input.
in case parameters are missing for a whole expression the whole
expression is skipped.
A even simpler expression would be a=1 or a=2 or ....... At the moment
i cannot generate such a constuct, which allows me to
define a select in one place, and then later add a or_(1,2,...) clause
at a certain point.As a special case i could use select().where(1).
where(2)... to get an and_(1,2,...)
An example :
Whenever the map window changes, i need to calculate the dataset which
falls out of the current window, and the ones which drops in.
Additionally i want to query the a modified sql expression whenever
the table changes (modified = with an additional in_ costraining to
pks in the table)
to do both i need to regenerate parts of the sql, but not all of it.
The way i do it now seems rather ugly because:
1) (partial_bound_func, ("funcarg")) is error prone ( I know i cold do
more reflection to find out argument numbers and names , but it would
in the end duplicate the bindparam mechanism )
2) to execute i have to:
- first look for parameters which are arguments to the partial
generative functions myselect= lazy_sql_unbound( user input params
for partial )
- then use the remaining parameters in session.execute( )
It just feels like all of this rather belongs into the lib, because it
could be all solved by allowing bindparam to have a value of type
SQLExpression.
moreover, the expression substitutions could accept bindparams as well.
As a last point , the compiler could check the validity, as it does
already.
regards
Paul Balomiri
paulbalom...@gmail.com
On 23.04.2010, at 15:26, Michael Bayer wrote:
On Apr 23, 2010, at 6:58 AM, Paul Balomiri wrote:
Hi,
Several days ago i has a similar question, which
was, perhaps a bit too theoretical. Here is a simple case:
select(text(select * from f(:time)) )
can I supply alternatively either
{time: datetime.datetime(1999,9,9,9,9,9)}
or
{time: " now()"}
I cannot get around that sqlalchemy interprets " now()" as a
string, while i try to use the postgres(or other backends) now()
function.
bind parameters exist only for the purpose of specifying literal
data to be injected as the values into a SQL statement. They
cannot be used to modify the lexical structure of a statement.
So a lexical unit like "CURRENT TIMESTAMP" or "NOW()" is part of
the statement's lexical source and cannot be injected as a bind
parameter.
To put it another way, bind parameters are not just string
substitutions the way something like "foo %s" % ('bar') is in
Python, even though they may look that way.
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