* Emanuele Zeppieri <[EMAIL PROTECTED]> [2007-09-07 11:15]:
> Mark Lawrence wrote:
> >If that is so, then you are asking how the following is
> >evaluated?
> >
> > ($track->length > 248) & ! ($cd->year < 1997)
>
> No, I'm asking how it could be *built* by code without string
> concatenations/interpolations.
Uh. They’re Perl expressions. Don’t you know how to write
conditionally executed Perl expressions? What are you doing on
this list? :-)
use List::Util qw( reduce );
my @cond;
# in real code the following stuff would be more systematic;
# this is just to demonstrate the principle
if ( $min_track_length ) {
push @cond, $track->length > $min_track_length;
}
if ( $max_year ) {
push @cond, $cd->year < $max_year;
}
my @where = @cond
? ( where => reduce { $a & $b } @cond )
: ();
$schema->query(
select => [$track->title, $cd->year],
from => [$track, $cd],
distinct => 1,
union => $query2,
@where,
);
This could be a bit simpler if SQL::DB provided an interface
shortcut so I didn’t have to do the fiddly bit with the [EMAIL PROTECTED]
array there.
At minimum it would consider `where => undef` to be an empty
constraint, so `where => reduce { $a & $b } @cond` would work
(since `reduce` returns undef when the input list is empty). This
would allow maximum control, since I can use a specific operator
of my choosing in the `reduce` block.
For simpler cases maybe it could take multiple separate `where`
clauses that get ANDed, in which case I could just say
if ( $min_track_length ) {
push @cond, where => $track->length > $min_track_length;
}
if ( $max_year ) {
push @cond, where => $cd->year < $max_year;
}
$schema->query(
select => [$track->title, $cd->year],
from => [$track, $cd],
distinct => 1,
union => $query2,
@cond,
);
Mark, are you listening?
Regards,
--
Aristotle Pagaltzis // <http://plasmasturm.org/>
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