set_relation with value field for WHERE

Hi.
Can i get current value of field for un parameter of set_relation .

I have this table :

CREATE TABLE personne(
  numpersonne serial NOT NULL,
  nom character varying(20) NOT NULL,
  prenom character(20) NOT NULL,
  datenaissance date,
  codepostalpers bigint NOT NULL,
  ----------
  refcommune integer,
  ----------
  ...

refcommune is a foreign key and i use set_relation to the table commune :

 CREATE TABLE commune(
  numcommune serial NOT NULL,
  commune character varying(50) NOT NULL,
  codepostal character(5) NOT NULL,
  CONSTRAINT pk_commune PRIMARY KEY (numcommune )
)

my code

 $crud->set_theme('datatables');
    $crud->set_table('personne');    
    $crud->fields('nom','prenom','datenaissance','codepostalpers','refcommune');
    
    $crud->set_relation('refcommune','commune','{codepostal} - {commune}', array('codepostal' => XXXXXXXXXXX) );

In set_relation with the 4Â° parameter : With the constant '31000' for codepostalpers it's Ok
I have the rows of commune with '31000'

$crud->set_relation('refcommune','commune','{codepostal} - {commune}', array('codepostal' => '31000') );

but i want to use the current value of codepostalpers of my table personne

$crud->set_relation('refcommune','commune','{codepostal} - {commune}', array('codepostal' => XXXXXXXXXXXXXXX) );

How replace XXXXXXXXX by the field codepostalpers of my grid ?

THX for help and time.

set_relation with value field for WHERE

eric