inflating columns to objects

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I'm having a problem on a Maypole edit page, but I think the problem is 
something I'm doing wrong in Class::DBI with respect to Class::DBI::AsForm.

I'm trying to use an object to represent a column:

    seq   LONGTEXT NOT NULL,
    INDEX (seq(10))

The value in the database is a potentially long string (and that is what 
I want to keep in the database :) but when it is displayed, I want to 
format it into lines of a reasonable length. I have written a class (see 
below) and added this line in my driver class (which isa Class::DBI):

    QD1::Sequence->has_a(seq => 'my_seq', deflate => 'deflate');

This works when displaying a list, but when I click on edit I get an
empty space where the textbox should be:

    <p><b>Seq</b>: </p><input TYPE="submit" NAME="edit" VALUE="edit">

Can anybody see what am I doing wrong?

Thanks, Dave
        -- 
        
package my_seq;

# Class to prepare seq column entries for display

use strict;
use warnings;

use overload ( '""'  => \&display );

our $VERSION = '0.01';
my $line_length = 60;

# A blessed array [$value] would be better than the single-element hash
# but HTML::Element can't cope with that :(

sub new
{
   my ($proto, $value) = @_;
   my($class) = ref $proto || $proto;
print STDERR "my_seq::new\n";
   bless {seq=>$value}, $class;
}

sub display
{
   my $self = shift;
print STDERR "my_seq::display\n";
   my $seq  = $self->{seq};
   my $length = length $seq;
   my @result;
   for (my $pos = 0; $pos < $length; $pos += $line_length)
   {
    push @result, substr($seq, $pos, $line_length);
   }

   return join "\n", @result;
}

sub deflate
{
print STDERR "my_seq::deflate()\n";
   return $_[0]->{seq};
}

sub line_length
{
   my $self = shift;
   $line_length = $_[0] if @_ and $_[0] >= 1;
   return $line_length;
}


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-- 
Dave Howorth
MRC Centre for Protein Engineering
Hills Road, Cambridge, CB2 2QH
01223 252960