[Dbix-class] Re: [OT][ANNOUNCE] SQL Generation with SQL::DB

[A. Pagaltzis]

Hi Emanuele,

* Emanuele Zeppieri <ema_zep at libero.it> [2007-09-07 13:25]:
> A. Pagaltzis wrote:
> 
> >* Emanuele Zeppieri <ema_zep at libero.it> [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 )
> >        : ();
> >
> 
> ROTFL! :-)
> 
> Not only a bunch of reduce()'s are mainteinibility-wise even
> worse than string concatenations

News to me.

I can only see one `reduce` in that code, btw.

But anyway, `reduce` shouldn’t be necessary here, the SQL::DB API
could do that work internally. But I’ve already said that.

> (did you understand that also subexpressions like:
> "$track->length > $min_track_length"
> and
> "$track->length > $min_track_length"
> must be built *dinamically*, from arbitrarly user data, not
> statically in the code as you did in your example? :-)

How is my code not building them dynamically? If
$min_track_length has no value, then that condition is not added
to the code. Please explain to me how your SQLA data structure
manipulation code is somehow more dynamical than that.

Actually, go ahead: post some magic dynamical SQLA query builder
code that I can’t translate to SQL::DB. Let’s watch me fail.

> but, if you perform a sequence of reduce()'s, you should even
> find the correct order to honor the operators precedences.

`reduce` folds left to right. What things are more to the left
and which are more to the right in the array will depend on the
order in which I put them in the array.

Funnily enough, that means I have to pay attention to exactly the
same things as I would have had to if I were building SQLA query
data structures.

> Basically, you're rewriting an SQl parser, thus fully bypassing
> the SQL::DB expression parser (and reimplementing it in your
> code, congratulations! :-)

Point me to which part of my code does any parsing.

Point me to which part of my code is conceptually different from
what an SQLA data structure builder snippet does.

> You did consider that, right?

Why should I? It’s wrong.

> So, who should reconsider his presence on this list? (as well
> as in the programming world in general :-)

Oh crap, you’re right. I should pack my bags and leave. :-)

Regards,
-- 
Aristotle Pagaltzis // <http://plasmasturm.org/>