The problem is that the line item type is configured per node type. Sometimes the site architecture works out and this isn't a big deal. However, sometimes the requirements would make you create far too many node types, have to manage an insane amount of field instance configurations, and cause a lot of discrepancies across configurations. Below is a snippet that allows you to programmatically set the line item type, allowing you to choose based off the form's context and reducing the required number of content types.
The form is built in two ways: hook_field_formatter_view() and field_attach_view_alter(). The latter hook is when Commerce Cart works it's magic, so we need to intercept and inject ourselves right in the middle. But how? Drupal runs hooks based on module weight and then based on the name in alphabetical order. That's a pain to guess, so first add a hook_module_implements_alter() to force your hook to run first.
$implementations[$module]);
unset($implementations[$module]);
$implementations = $group + $implementations;
}
?>
Essentially we're hooking into Drupal's hook system to say "when invoking this alter, run ours first" in a play of hookception. Now we add our hook_attach_view_alter to modify the line item type before it hits Commerce Order
$element) {
if (!empty($element['#formatter']) && $element['#formatter'] == 'commerce_cart_add_to_cart_form') {
foreach (element_children($element) as $key) {
// Store the current line item type
$line_item_type = $output[$field_name][$key]['#arguments']['line_item']->type;
// Check to make sure we're not already using a custom line item type.
if ($line_item_type == 'product') {
// In this example, we'll switch line item type based on catalog tid
$store_category = $context['entity']->field_store_category[LANGUAGE_NONE][0]['tid'];
// If not set to custom line item type already, override by term ID.
if ($store_category == '87') {
$line_item_type = 'my_line_item_type';
}
elseif ($store_category == '36') {
$line_item_type = 'my_other_line_item_type';
}
$output[$field_name][$key]['#arguments']['line_item']->type = $line_item_type;
}
}
}
}
}
?>
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