public function initialize()
{
$this->setSource('issue12071_body');
$this->belongsTo('head_1_id', Head::class, 'id', ['alias' => 'head1', "foreignKey" => ["allowNulls" => true, "message" => "First head does not exists"]]);
$this->belongsTo('head_2_id', Head::class, 'id', ['alias' => 'head2', "foreignKey" => ["allowNulls" => true, "message" => "Second head does not exists"]]);
}