Apply discount when purchasing a mix of products from the same product display

oh excellent, i'd forgotten about this but would still be useful, thanks Cybso, will test it out ASAP.

Tested and works exactly as required, thanks a lot.

OK I have come across a stumbling block here, this solution works perfectly when creating orders through the shopping cart but doesn't work when creating an order manually through the back end.

Initially the price table didn't function at all when creating an order through the back end so I am using this module here ( http://drupal.org/project/commerce_checkout_admin ) to allow the rules that update prices from the price table to fire when an order is saved through the back end.

The reason it doesn't work is that $line_item->commerce_display_path is empty when not creating an order using the shopping cart, I'm not sure how to get around this.

Thanks for the pointers - will give that a go.

ok this it what I have now - my php skills and knowledge of the commerce tables are pretty flaky so I suspect it's not very elegant but it seems to work!

        // Apply discount when purchasing a mix of products from the same product display
	if ($display_path = @$line_item->commerce_display_path['und'][0]['value']) {
		$query = db_select('commerce_line_item', 'cli');
		$query->addExpression('SUM(cli.quantity)', 'quantity');
		$query->innerJoin('field_data_commerce_display_path', 'dp', 'dp.entity_id = cli.line_item_id');
		$query->condition('cli.order_id', $line_item->order_id, '=');
		$query->condition('dp.entity_type', 'commerce_line_item', '=');
		$query->condition('dp.commerce_display_path_value', $display_path, '=');
		if ($result = $query->execute()->fetchField()) {
			$quantity = $result;
		}
	}
	else if (empty($line_item->commerce_display_path['und'][0]['value'])) {
		$query = db_select('field_data_commerce_product', 'fdcp');		
		$query->addExpression('SUM(cli.quantity)', 'quantity'); 
		$query->innerJoin('field_data_field_product', 'fdfp', 'fdfp.field_product_product_id = fdcp.commerce_product_product_id');
		$query->innerJoin('field_data_field_product', 'fdfp2', 'fdfp2.entity_id = fdfp.entity_id');
		$query->innerJoin('field_data_commerce_product', 'fdcp2', 'fdcp2.commerce_product_product_id = fdfp2.field_product_product_id');
		$query->innerJoin('commerce_line_item', 'cli', 'cli.line_item_id = fdcp2.entity_id');
		$query->innerJoin('field_data_commerce_line_items', 'fdcli', 'fdcli.commerce_line_items_line_item_id = cli.line_item_id and fdcli.entity_id = cli.order_id');
		$query->condition('fdcp.entity_id', $line_item->line_item_id, '=');
		$query->condition('cli.order_id', $line_item->order_id, '=');
		$query->condition('fdcp.entity_type', 'commerce_line_item', '=');
		$query->condition('fdcp.bundle', 'product', '=');
		$query->condition('fdfp.entity_type', 'node', '=');
		$query->condition('fdfp.bundle', 'product_display', '=');
		$query->condition('fdfp2.entity_type', 'node', '=');
		$query->condition('fdfp2.bundle', 'product_display', '=');
		$query->condition('fdcp2.entity_type', 'commerce_line_item', '=');
		$query->condition('fdcp2.bundle', 'product', '=');
		$query->condition('fdcli.entity_type', 'commerce_order', '=');
		$query->condition('fdcli.bundle', 'commerce_order', '=');
					
		if ($result = $query->execute()->fetchField()) {
			$quantity = $result;
		}
	}