Limit number of purchase of certain item or multiple items

[fs_xyz]

Hi,
Not sure if this is the correct section. Just wanted to contribute something with modification which I managed to do.
This is about limiting purchase of an item. For example in the code is product with product id = 2, and the limit is 1.

If you're not sure with what is your product id, you can see the list from catalog->product menu at admin page under 'ID' column.

The modification is in file controllers/front/CartController.php. The modification worked for 1.5 and 1.6.
Find this function around line 190 ish.
 

protected function processChangeProductInCart()
{
	$mode = (Tools::getIsset('update') && $this->id_product) ? 'update' : 'add';
		
	if ($this->qty == 0)
		$this->errors[] = Tools::displayError('Null quantity.', !Tools::getValue('ajax'));
	elseif (!$this->id_product)
		$this->errors[] = Tools::displayError('Product not found', !Tools::getValue('ajax'));

I put modification to become :

protected function processChangeProductInCart()
{
	$mode = (Tools::getIsset('update') && $this->id_product) ? 'update' : 'add';
               
        //this is to prevent user to multiple click 'add to cart' button and add more than 1 when inputing number of purchase
	if (($this->qty > 1) && ($this->id_product == 2))
		$this->errors[] = Tools::displayError('This product is limited to one quantity in purchase', !Tools::getValue('ajax'));
		
        //this one is for checkout page where this will disable plus button upon press and produce message when pressed
	if (($this->context->cart->id) && ($this->id_product == 2)) {
		$db = Db::getInstance();
		$result = $db->getValue('
			SELECT quantity as pur_num
			FROM '._DB_PREFIX_.'cart_product
			WHERE id_product = 2 AND
				id_cart = '.$this->context->cart->id);
		if ($result>=1)
			$this->errors[] = Tools::displayError('This product is limited to one quantity in purchase', !Tools::getValue('ajax'));
	}
		
	if ($this->qty == 0)
		$this->errors[] = Tools::displayError('Null quantity.', !Tools::getValue('ajax'));
	elseif (!$this->id_product)
		$this->errors[] = Tools::displayError('Product not found', !Tools::getValue('ajax'));

Hopefully, this can help. Sorry for bad english, not my 1st language.

[fs_xyz]

If you need to set more rules, you can use this :
 

//this part to prevent multi 'add to cart' button usage on the same product and 
//to prevent input bigger than your limit when inputing number of purchase
switch ($this->id_product) {
    case 1: //example of product id, change to any number you want
        if ($this->qty > 1) //you can change 1 to any number you want as product limit
            $this->errors[] = Tools::displayError('This product is limited to one quantity in purchase', !Tools::getValue('ajax'));
        break;
    case 2:
        if ($this->qty > 1)
            $this->errors[] = Tools::displayError('This product is limited to one quantity in purchase', !Tools::getValue('ajax'));
        break;
    case 3:
        if ($this->qty > 1)
            $this->errors[] = Tools::displayError('This product is limited to one quantity in purchase', !Tools::getValue('ajax'));
        break;
} //if you need more items, just re-do one of those 'case' command.

//this part to disable 'plus' button on checkout page if the number went bigger or user change the number
//you will need the same number of 'case' command depend on previous usage.

$db = Db::getInstance();
switch ($this->id_product) {
    case 1: 
        $result = $db->getValue('
		SELECT quantity as pur_num
		FROM '._DB_PREFIX_.'cart_product
		WHERE id_product = 1 AND
			id_cart = '.$this->context->cart->id);
        if ($result>=1)
	    $this->errors[] = Tools::displayError('This product is limited to one quantity in purchase', !Tools::getValue('ajax'));
        break;
    case 2:
        $result = $db->getValue('
		SELECT quantity as pur_num
		FROM '._DB_PREFIX_.'cart_product
		WHERE id_product = 2 AND
			id_cart = '.$this->context->cart->id);
        if ($result>=1)
	    $this->errors[] = Tools::displayError('This product is limited to one quantity in purchase', !Tools::getValue('ajax'));
        break;
    case 3:
        $result = $db->getValue('
		SELECT quantity as pur_num
		FROM '._DB_PREFIX_.'cart_product
		WHERE id_product = 3 AND
			id_cart = '.$this->context->cart->id);
        if ($result>=1)
	    $this->errors[] = Tools::displayError('This product is limited to one quantity in purchase', !Tools::getValue('ajax'));
        break;
}

Well, this modification is useful to those who only require small amount of items require this purchase rule. For those with larger, you might need module for this.

[AivarasKar]

Hello, 

 

It works fine, but I cant see error on product and category page when adding to cart. What could be a problem?