On Apr 23, 2010, at 12:13 PM, Paul Balomiri <paulbalom...@gmail.com>
wrote:
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.
A bind parameter is not a sqlalchemy invention - it would be wrong
for us to redefine the term "bind parameter" to mean something
entirely different within the library. It is also not permitted by any
dbapi so it is impossible in any case.
You can acheive mostly the result you want using a custom SQL
expression construct, in conjunction with sqlalchemy.ext.compiler.
The construct would peek into a context-specific dictionary for its
contents at compile time and forward onto it's corresponding
construct. You'd stick the dictionary on the the outermost
containing construct, which you can then grab from the compiler
instance.
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.
--
You received this message because you are subscribed to the
Google Groups "sqlalchemy" group.
To post to this group, send email to sqlalch...@googlegroups.com.
To unsubscribe from this group, send email to sqlalchemy+unsubscr...@googlegroups.com
.
For more options, visit this group at http://groups.google.com/group/sqlalchemy?hl=en
.
--
You received this message because you are subscribed to the Google
Groups "sqlalchemy" group.
To post to this group, send email to sqlalch...@googlegroups.com.
To unsubscribe from this group, send email to sqlalchemy+unsubscr...@googlegroups.com
.
For more options, visit this group at http://groups.google.com/group/sqlalchemy?hl=en
.
--
You received this message because you are subscribed to the Google
Groups "sqlalchemy" group.
To post to this group, send email to sqlalch...@googlegroups.com.
To unsubscribe from this group, send email to sqlalchemy+unsubscr...@googlegroups.com
.
For more options, visit this group at http://groups.google.com/group/sqlalchemy?hl=en
.
--
You received this message because you are subscribed to the Google
Groups "sqlalchemy" group.
To post to this group, send email to sqlalch...@googlegroups.com.
To unsubscribe from this group, send email to sqlalchemy+unsubscr...@googlegroups.com
.
For more options, visit this group at http://groups.google.com/group/sqlalchemy?hl=en
.
--
You received this message because you are subscribed to the Google Groups
"sqlalchemy" group.
To post to this group, send email to sqlalch...@googlegroups.com.
To unsubscribe from this group, send email to
sqlalchemy+unsubscr...@googlegroups.com.
For more options, visit this group at
http://groups.google.com/group/sqlalchemy?hl=en.
