Commerce - adding a product to a cart programmatically with custom price

Question

I've got a line item type called 'Donation' which has a Product reference field.

Additionally, I have an instance of a Product type called 'Donation' with the SKU of DONATION_ONEOFF (pid=1), which has a price field set to $0.

What I want to do is decide at form submit time what the value of the line item is before I add it to the cart.

I have a test form, that when submitted, runs the following

function jam_test_donation_form_submit($form, &$form_state) {
    global $user;

    // Load the product with SKU DONATION_ONEOFF
    $product = commerce_product_load(1);

    // Try and set the price of the product before passing it.
    $product->commerce_price['und'][0]['amount'] = 22;

    // Create the line item from the product.
    $line_item = commerce_product_line_item_new($product, 1, 0, array());

    // Add the line item to the cart.
    $line_item_added = commerce_cart_product_add($user->uid, $line_item);
}

I was hoping that the new value (22) would display in the Cart, but it's still at 0 - even though the $line_item and $line_item_added objects show the correct field values of 22 and even a calculated total if I add more.

I assume this could be because the cart is referencing the product node directly rather than using the value it was given at commerce_cart_product_add time - is there something I need to call to update this?

I could create a series of products at fixed amounts but I need the ability to specify an arbitrary amount for donation as well.

Answer 1

This is covered at length in a variety of other places. Your price is being lost due to the shopping cart refresh system and your avoidance of the core product pricing API.

You need a custom price field or something to store the price on the line item and then a pricing rule that swaps that custom price in for the unit price during the price calculation process.