__PACKAGE__->add_columns(
  "uco" =>  {
    accessor    => "username",
    data_type   => "text",
    is_nullable => 0,
    original    => { data_type => "varchar" },
  },
  ...
);

$rs->search( { username => { '!=', $row->username }, ... );

my $accessor = $field->accessor;
 
my $count = $rs->search( { $accessor => $value, @id_clause } )->count;

use List::Util 1.29 qw/ pairmap /;

# These aliases could probably be saved in an attribute

my %aliases = pairmap  { $b->{accessor} || $a => $a, $a => $a }
        %{ $self->resultset->result_source->columns_info };

my $accessor = $field->accessor;
my $column = $aliases{ $accessor } || $accessor;
 
my $count = $rs->search( { $column => $value, @id_clause } )->count;