Cakephp habtm relation updating instead of saving - cakephp

Question

Hello my problem is i try to save a new relation between a shop and a payment method
the relation is habtm... shop and payment already exist. i want to ad more payment methods.
But always when i save ,the old payment realtion in the shop_payment table is only updated, not a second one saved....
i read a lot i set unique to false but nothing changes that.
Anyone got an idea?
Model
class Payment extends AppModel {
var $hasAndBelongsToMany = array(
'Mainshop'=>array('className'=>'Mainshop', 'unique'=>'false')
);
}
View
echo $this->Form->create('Mainshop');
echo $this->Form->input('name',array('default'=>$mainshop['Mainshop']['name']));
echo $this->Form->input('Payment.id', array(
'type' => 'select',
'options' => array($payments),
));
echo $this->Form->input('id', array('type'=>'hidden','value'=>$mainshop['Mainshop'] ['id']));
echo $this->Form->end('Edit Shop');?>
Controller
if (!empty($this->data)){
$this->Mainshop->save($this->data);
$this->redirect(array('action' => 'edit',$this->data['Mainshop']['id']));
}

Answer 1

My recommendation defines the relationship with all fields in model:
var $hasAndBelongsToMany = array(
'Mainshop'=>array(
'className'=>'Mainshop',
'unique'=>'false',
'joinTable' => 'shop_payments',
'foreignKey' => 'payments_id',
'associationForeignKey' => 'shop_id'
)
);
In the controller add create():
if (!empty($this->data)){
$this->Mainshop->create();
$this->Mainshop->save($this->data);
$this->redirect(array('action' => 'edit',$this->data['Mainshop']['id']));
}