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Re^2: A Case with 5 Var's

by davorg (Chancellor)
on Jan 25, 2007 at 12:36 UTC ( #596462=note: print w/replies, xml ) Need Help??

in reply to Re: A Case with 5 Var's
in thread A Case with 5 Var's

I've no idea what kind of "qry" you're talking about. But let's assume you want a database query where the contents of the where clause are controlled by the existance of data items that are stored in a hash. The keys of the hash are the column names and the values are the values that are required.

In the past I've used code something like this:

my $sql = 'select col_x, col_x from a_table'; # You'll be setting this hash up from some kind of # input to your program. I'm using variables for # illustrative purposes. my %cols = ( col_x => $foo, col_y => $bar, col_z => $baz, ); my @where; my @vals; foreach (keys $cols) { if (defined $cols{$_}) { push @where, "$_ = ?"; push @vals, $cols{$_}; } } if (@where) { $sql .= ' where ' . join(' and ', @where); } my $sth = $dbh->prepare($sql); $sth->execute(@vals);

Update: Or use SQL::Abstract as Corion points out.

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Re^3: A Case with 5 Var's
by ultibuzz (Monk) on Jan 25, 2007 at 16:13 UTC

    i'm testing a combined hash and bit solution wich untill now looks great,
    thx for the great help and examples
    kd ultibuzz

      If your query consists of embedding the available data into a string in a specific order, you could just interpolate it:
      my $query = ":$name:$vorname:$plz:$tel:$tel49:";
      If the query structure needs to look different for each combination of data, you could use the bit vector you're constructing to access a hash:
      my %query_for = ( 0 => "::", 1 => "name IS \$name", 2 => "vorname IS \$name", ... );
      You'd need 2^5 (32) entries in the hash if every possible combination of the five items was valid; if not, you could leave out any invalid combinations. This means that if $query_for{$bit_vector} was undef, you'd know you had an invalid combination without any comparison logic at all.

      Note that I escaped the "query" strings; that way, you can do an eval on the string and interpolate the variables into the query at the time you have the values you want. If the variables weren't escaped, whatever values they had (probably undef) at the time the hash was constructed would be substituted in immediately, and you'd always get queries without any data in them.

      A much more advanced way to do it is to use anonymous subroutines as the entries in the hash:

      my %query_constuctor_for = ( ... 18 => sub { return ":NIL/$vorname::$tel49:" }, 19 => sub { return ":$name/$vorname::$tel49:" }, ... );
      Lookup works the same way, but you'd say
      my $query_maker = $query_constructor_for{$bitvector}; defined $query_maker or die "Combination invalid"; $query = $query_maker->()
      to get your query; the $query_maker->() expression calls the anonymous subroutine that you looked up with $query_constructor_for{$bitvector}. This lets you construct arbitrarily-complicated code to do what's needed for each combination.

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[Corion]: This is a toy clone of Jekyll, currently named MrHyde. But maybe I'll change that name to Jokel / Yokel, or some other play on the name , still mildly unfunny ;)
[choroba]: Or maybe Utterson?

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