How To Force Commerce Cart View To Update (Ajax?)

Question

I admit to being a Commerce -novice-. It's getting better, but it's still quite confusing in some spots. I've posted several questions here over the past year trying to skin the same cat in different ways. We have a Drupal 7 cart. The pricing is pulled in from an external web site via http_request which updates the unit price of all items in the cart on hook_form_alter().

The problem is that the -initial- price that displays in the cart is always 0. The user always has hit to refresh the page for that pricing to update the View. Commerce seems to want to pull the unit price in from the Product nodes so after a user hits the cart displays but with a 0 unit price. When they hit -then- our code fires and updates the price.

So... I need is either: a) a way to force that view to 'refresh' when the page is rendered (ie. it initially loads with the zero prices, runs the http_request code and -then- renders again). Yeah, it's ugly but I'm just sick of this.

b) Figure out a way using the Rules (which I haven't been able to do) to get the line item price to pull in from the http_request with PHP. This -never- seems to work. It -always- wants to use a rule based on an existing field. If someone could give me a tutorial on how to use PHP with Commerce for the Unit Price I'd buy them a CASE of virtual beer!

c) Figure out a way to assign that http_request price as the line item price when the user hits the 'Add' button. Again, probably a noob thing, but I cannot figure out how to override the Unit Price for the Line Item to the value I want. It -always- wants to use the Unit Price from the Product node.

ANY help would be most appreciated!

Answer 1

Implement a custom rules action and wire it to rules event Calculating the sell price of a product. The sell price of a line item can be forced to any value using the action Set the unit price to a specific amount. The missing piece is a custom rule action capable of retrieving the amount. As a starting point I propose the following (assuming the custom module is named acme):

/**
 * Implements hook_rules_action_info().
 */
function acme_rules_action_info() {
  return array(
    'acme_random_amount' => array(
      'label' => t('Generate random price (with params!)'),
      'group' => t('Examples'),
      'parameter' => array(
        'product_id' => array(
          'type' => 'text',
          'label' => t('Product SKU'),
          'description' => t('The SKU of a product.'),
        ),
        'account' => array(
          'type' => 'user',
          'label' => t('User'),
          'description' => t('A user account.'),
        ),
      ),
      'provides' => array(
        'amount' => array(
          'type' => 'decimal',
          'label' => t('Amount'),
          'description' => 'Return a random numeric amount, except for admin.',
        ),
      ),
    ),
  );
}

/**
 * Rules action: Generate and return random amount of money.
 */
function acme_random_amount($product_id, $account) {
  $amount = mt_rand(100, 1000);

  // Fix price for admin.
  if ($account && $account->uid == 1) {
    $amount = 420;
  }

  // Blue sells, let's boost the revenue.
  if (strpos($product_id, 'BLU') !== FALSE) {
    $amount *= 100;
  }

  return array(
    'amount' => $amount,
  );
}

The rule then looks something like this:

{ "rules_pick_random_price" : {
    "LABEL" : "Pick random price",
    "PLUGIN" : "reaction rule",
    "REQUIRES" : [ "rules", "acme", "commerce_line_item", "commerce_product_reference" ],
    "ON" : [ "commerce_product_calculate_sell_price" ],
    "IF" : [
      { "entity_has_field" : { "entity" : [ "commerce-line-item" ], "field" : "commerce_product" } }
    ],
    "DO" : [
      { "acme_random_amount" : {
          "USING" : {
            "product_id" : [ "commerce-line-item:commerce-product:sku" ],
            "account" : [ "commerce-line-item:order:owner" ]
          },
          "PROVIDE" : { "amount" : { "amount" : "Amount" } }
        }
      },
      { "commerce_line_item_unit_price_amount" : {
          "commerce_line_item" : [ "commerce_line_item" ],
          "amount" : [ "amount" ],
          "component_name" : "base_price",
          "round_mode" : "0"
        }
      },
      { "drupal_message" : { "message" : "Set the price of [commerce-line-item:commerce-product:sku] to amount: [amount:value] for user [commerce-line-item:order:owner:name]" } }
    ]
  }
}

Note that in order to get at the product SKU, it is necessary to introduce a condition Entity has field checking for the presence of the commerce_product field on the commerce-line-item variable.

Please keep in mind that this rule will be executed on every page request for every item in the cart. Additionally it is executed whenever an add-to-cart form is displayed. If this is on a high traffic site, you probably need to think about an appropriate caching strategy.