Syntax question when using Class::DBI

freddo411 has asked for the wisdom of the Perl Monks concerning the following question:

Monks,

I'm stuck on a syntax problem. I'm using Class::DBI which lets me get at values of fields within a DB by treating each row as an object. So normally I'd refer to my "id" as:

  print $rowobj->id;
[download]

OK so far, but now I need to be more dynamic, like so:

  my $columnname = 'id';
  print $rowobj->$columnname;
[download]

but this gives me an syntax error when I perl -c my code.

How do I use a variable value in this case?

-------------------------------------
Nothing is too wonderful to be true
-- Michael Faraday

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Re: Syntax question when using Class::DBI by fglock (Vicar) on Dec 09, 2004 at 01:47 UTC
This syntax does work in 5.005_03 - but you may have to add parenthesis to make it clear that you are calling a method: `my $columnname = 'id'; print $rowobj->$columnname();` [download]	[reply] [d/l]
Re^2: Syntax question when using Class::DBI by Your Mother (Archbishop) on Dec 09, 2004 at 03:17 UTC
Thank you. I had this problem at work last week where I don't get to pick the perl version :) and resorted to `no strict 'refs'; &{etc...`	[reply] [d/l]
Re^2: Syntax question when using Class::DBI by fglock (Vicar) on Dec 14, 2004 at 21:10 UTC
Just for reference - The ever-growing reference table of backwards 5.005_03 compatibility: 289351	[reply]
Re: Syntax question when using Class::DBI by broquaint (Abbot) on Dec 09, 2004 at 01:13 UTC
There is no problem with using a simple scalar variable when dynamically calling a method, as Fletch illustrated. However if you're using an aggregate variable or an expression you can simply use the `can` method e.g `print $rowobj->can( $cols{id} )->();` [download] Or if you wish to call it directly you need to be a little indirect and take advantage of scalar dereferencing e.g `print $rowobj->${ \$cols{id} };` [download] Addendum: On a more practical note you can always access the primary key by using the `id` accessor method, regardless of what is the name of the actual row; as documented. HTH `_________ broquaint`	[reply] [d/l] [select]
Re: Syntax question when using Class::DBI by perrin (Chancellor) on Dec 09, 2004 at 01:26 UTC
That should work, but you can also use the get() accessor: `$rowobj->get($columnname)` [download]	[reply] [d/l]
Re: Syntax question when using Class::DBI by Fletch (Bishop) on Dec 09, 2004 at 00:58 UTC
That's perfectly valid syntax (although more paranoid code would check with `UNIVERSAL::can` before calling arbitrary methods). `freebie:~ 973> cat fooble + 19:55:47 my $columnname = 'id'; print $rowobj->$columnname; freebie:~ 974> perl -wc fooble + 19:55:48 Name "main::rowobj" used only once: possible typo at fooble line 2. fooble syntax OK` [download] Your problem's elsewhere.	[reply] [d/l] [select]
Re^2: Syntax question when using Class::DBI by freddo411 (Chaplain) on Dec 09, 2004 at 01:28 UTC
fooble syntax OK Your problem's elsewhere. Scratches head ... Really, I'm not crazy: `gonzo:: more foo.pl #!/usr/local/bin/perl my $columnname = 'id'; print $rowobj->$columnname; gonzo:: perl -c foo.pl syntax error at foo.pl line 4, near "$columnname;" foo.pl had compilation errors.` [download] OK, how about that fact that I'm running an ancient perl 5.005. That would explain our different results. And the solution for 5.005 is staring at me in another NOOBs question: `my $columnname = 'id'; print $rowobj->{$columnname};` [download] Cheers ------------------------------------- Nothing is too wonderful to be true -- Michael Faraday	[reply] [d/l] [select]
Re^3: Syntax question when using Class::DBI by Corion (Patriarch) on Dec 09, 2004 at 08:18 UTC
Be aware that Class::DBI lazy-loads the columns, so as soon as you start using the `Essential` feature for columns, you might find `$rowobj->{$columnname}` empty even though there is a value in the column. Using the `get` method should make sure that your object gets filled with data.	[reply] [d/l]