multi-column PK and has_many

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I have two tables from an existing schema that I want to set up a 
relationship between.  Table A has a single column primary key (call it 
ta_id).  Table B has a 3-column primary key, and one of those columns is 
ta_id from Table A.  This is the column that relates these two tables.  
Any particular ta_id can occur many times in Table B (hence the 
multi-column primary key) and so the usual has_a/might_have relationship 
that I would use for a primary key shared between two tables doesn't 
work.  Also a has_a/has_many tries to inflate the ta_id in the Table B 
object and that's a bad thing.  I want to be able to return an instance 
of Table B, but with only a limited number of it's fields, but has_many 
doesn't seem to offer me the option of listing @feilds_to_import like 
might_have does - Music::CD->might_have(method_name => Class => 
(@fields_to_import));

Shown below are my actual tables and the Classes that I have set up to 
represent them.  The two commented perl lines are the ones dealing with 
the relationship I'm discussing.  The has_many as shown calls a method 
on the Table B object.  I need an instance.

Any thoughts???

Seqfeature Table (aka Table A)
------------------------------
seqfeature_id   integer    PRIMARY KEY # aka ta_id
bioentry_id     integer    UNIQUE NOT NULL
type_term_id    integer    UNIQUE NOT NULL
source_term_id  integer    UNIQUE NOT NULL
display_name    varchar(64)
rank            integer    UNIQUE NOT NULL

Seqfeature_qualifier_value Table (aka Table B)
seqfeature_id  integer    PRIMARY KEY #aka ta_id
term_id        integer    PRIMARY KEY
rank           integer    PRIMARY KEY
value          text       NOT NULL

package Recode::SeqFeature_QV;
use base 'Recode::RecodeDB';
Recode::SeqFeature_QV->table('seqfeature_qualifier_value');
Recode::SeqFeature_QV->columns(Primary => qw/seqfeature_id term_id rank/);
Recode::SeqFeature_QV->columns(Others => qw/value/);
#Recode::SeqFeature_QV->has_a(seqfeature_id => 'Recode::SeqFeature');
Recode::SeqFeature_QV->has_a(term_id => 'Recode::Term');

###########################################################################################################

package Recode::SeqFeature;
use base 'Recode::RecodeDB';
Recode::SeqFeature->table('seqfeature');
Recode::SeqFeature->columns(All => qw/ seqfeature_id bioentry_id 
type_term_id source_term_id display_name rank/);
Recode::SeqFeature->has_a(bioentry_id => 'Recode::Bioentry');
Recode::SeqFeature->has_a(type_term_id => 'Recode::Term');
Recode::SeqFeature->has_a(source_term_id => 'Recode::Term');
#Recode::SeqFeature->has_many(seqfeature_qvs => [Recode::SeqFeature_QV 
=> 'term_id']);
Recode::SeqFeature->might_have(location_id => [Recode::Location => 
'seqfeature_id']);