accessing data in DBI object

[arcnon]

I cant seen to figure out how to access the the data in the DBI object and get it back in.

$Query_Statement="
SELECT fname,lname,address,city,state,zip,phone,email 
FROM main 
ORDER by lname,fname;";

    my $DataOut = $DBHandle->prepare($Query_Statement);
    $DataOut->execute();

foreach my $row_ref (@$DataOut->fetchrow_array){
        my $fname = @$row_ary[0];
        my $lname = @$row_ary[1];

        my $total += length($fname);
        my $total += length($lname);

        if ((length($fname) + length($lname)) > 18){
            my $Fintial = substr($fname,0,1);
            if ((length($Fintial) + length($lname)) > 18){
                $lname = substr($lname,0,16);
            }
            $row_ary[0] = $Fintial;
            $row_ary[1] = $lname;
        }
        else{
            next;
        }
    }

[polettix]

If you want to get an array ref, use fetchrow_arrayref instead of fetchrow_array. Then... use it instead of using $row_ary!

Update Of course, using array refs would lead to using $row_ref->[0] where you use $row_ary[0] - see perldoc perldata anyway.

[RazorbladeBidet]

Agreeing with frodo72 with an additional statement that using strict (i.e. adding "use strict;" at the top of your program) would have shown you that row_ary doesn't exist anywhere. Good to have (as well as "use warnings;")

Obviously, this is just a snippet. But I imagine you don't have it or it would have complained.

[arturo]

It helps us help you if you can say what's not working, e.g. what error message is perl giving you when you try to execute the code. That said, there are a couple of things that jumped out at me:

• foreach my $row_ref ... but inside the loop, you're referencing a thing you think is an array reference with the name row_ary; if you're using strict, this should be caught at compile time.
• you're getting an error message that looks like Not an ARRAY reference at your foreach line, because @$object->method treats $object as an array reference

(Also, what you probably meant to write ( @{$DataOut->fetchrow_array} ) won't work either, because fetchrow_array returns the row's data as an array.

So the following loop rewrite should help you get over the two problems I've mentioned:

  while ( my @row = $DataOut->fetchrow_array ) {
      my $fname = $row[0];
      # ...
  }

An even better solution, IMO, would be to use fetchrow_hashref so the columns have readable names and you don't have to go back to the SQL to figure out which column maps onto which variable.

HTH

[rnahi]

Have you seen our Tutorials?

There is one that may give you ideas: DBI Recipes.

[arcnon]

I own programming the perl dbi which pretty much the same thing.

I learn well from example but I could never find any info on accessing the object.

[JediWizard]

In addition to the comment made by the other monks, I'd like to describe a basic locigical flaw with this code. By using foreach my $row_ref (@$dataOut->fetchrow_array) you are actually iterating over columns, not rows. Changing this to use fetchrow_arrayref only changes it to be a foreach over a list with only one value (doesn't make any sense to do that). What you really meant to use there was fetchall_arrayref. This will return an array of arrays with all the data retrieved by your SQL query.

Update: After reading arturo's response, I'd like to add the following: using while(my @row = $dbh->fetchrow_array) is more memory efficient than using foreach my $row_ref ($dbh->fetchall_arrayref) but fetchall_arrayref may be faster (I'm not sure, it would depend on which DBD module was being used, you'd have to benchmark it). To speak to arturo's recomendation of using fetchrow_hash, it does make the code more maintainable, but less memory efficient, so it really depends on which is more important to you. You can achive the same effect as using fetchrow_hash using fetchall_arrayref by passing an empty hash ref in as an argument to the method.
HTH, Cheers

[arcnon]

I was just trying to get at 2 fields and change the data without having to create a new object. Which I did anyway...

I alway use strict. Yes it throws errors which just told me I wasn't accessing the structure right. But I already knew that. :)

References eat my lunch anyway. I use objects to dodge them to avoid @{}->[]->{} crap. So when I have to work with them(refs) I am always lost. my solution was as follows

$Query_Statement="select fname,lname,address,city,state,zip,phone,emai
+l FROM main order by lname,fname;";

    my $sth = $dbh->prepare($Query_Statement);
    $sth->execute();

    my @array;
    my $dataObjRef = \@array;

    while( my $array_ref = $sth->fetchrow_arrayref){
        #print ">>@$array_ref\n";

        my $fname = $array_ref->[0];
        my $lname = $array_ref->[1];


        my $total += length($fname);
        my $total += length($lname);

        if ((length($fname) + length($lname)) > 18){
            my $Fintial = substr($fname,0,1);
            if ((length($Fintial) + length($lname)) > 18){
                $lname = substr($lname,0,16);
            }
            $array_ref->[0] = $Fintial;
            $array_ref->[1] = $lname;

            #print "$Fintial    $lname\n";
        }
        else{
            next;
        }
        my @newArray = @$array_ref;
        push(@$dataObjRef, \@newArray);
    }

    $sth->finish();
    $dbh->disconnect or warn "Disconnection failed: $DBI::errstr\n";
    return $dataObjRef;
}

[Mr. Muskrat]

The only objects you have in this snippet are $dbh (a database handle object) and $sth (a statement handle object). (You called them $DBHandle and $DataOut in the original snippet.) The rest of the variables are just your ordinary garden variety variables: scalars, arrays and hashes. Objects are references (a scalar holding the address of another variable) that have been blessed into a given class. See perldata, perlref, perldsc, perllol, perlobj, perlmod, perltoot and perlboot for the complete details about Perl data types, references, Perl data structures, modules, and objects.