lib/components/dataInterface/connectors/db/Model.php
public function primaryKey()
    {
        $pk = $this->meta->schema->primaryKey;
        if (is_array($pk)) {
            $ppk = [];
            foreach ($pk as $key) {
                $ppk[] = $key;
            }

            return implode('.', $ppk);
        }

        return $pk;
    }
public function primaryKey()
    {
        $pk = $this->meta->schema->primaryKey;
        if (is_array($pk)) {
            $ppk = [];
            foreach ($pk as $key) {
                $ppk[] = $key;
            }

            return implode('.', $ppk);
        }

        return $pk;
    }
Retrieve the primary key column for the model item.

@return string the primary key