Index: uc_event_registration.module
===================================================================
--- uc_event_registration.module	(revision 2011)
+++ uc_event_registration.module	(working copy)
@@ -451,9 +451,23 @@
     // Fetch the product attributes from the webform submission because
     // uc_attribute components are in use.
     $attributes = _uc_event_registration_get_product_attributes($form, $form_state);
-
-    //add it to the cart
-    uc_cart_add_item($node->nid, $uc_event_quantity, array('attributes' => $attributes, 'uc_event_registration' => array('sid' => $sid_value)));
+    
+    // If we are editing an existing webform submission, update the associated cart item
+    if (isset($form_state['values']['details']['is_new']) && $form_state['values']['details']['is_new'] == false) {
+      // Fetch and update the cart item based on submission ID
+      $cart_item = uc_event_registration_get_cart_item_from_sid ($sid_value);
+      if ($cart_item) {
+        $cart_item->qty = $uc_event_quantity;
+        $cart_item->data['attributes'] = $attributes;
+        uc_cart_update_item($cart_item);
+        // Rebuild the cached cart items.
+        uc_cart_get_contents(NULL, 'rebuild');
+      }
+    }
+    else {
+      //add it to the cart
+      uc_cart_add_item($node->nid, $uc_event_quantity, array('attributes' => $attributes, 'uc_event_registration' => array('sid' => $sid_value)));
+    }  
   }
 }//end submit function
 
@@ -940,3 +954,88 @@
     unset($node->attributes);
   }
 }
+
+/**
+ * Implements hook_form_FORM_ID_alter() for webform_submission_delete_form to add a submit handler which removes a paidevent
+ * product from the cart.  The new submit handler appears before the default handler so it runs first.
+ */
+function uc_event_registration_form_webform_submission_delete_form_alter (&$form, &$form_state) {
+   // Add submit handler BEFORE the existing Webform submit handler
+   $form['#submit'] = array_merge(array('uc_event_registration_webform_submission_delete_form_submit'), $form['#submit']);  
+}
+
+/**
+ * Webform submission delete form submit handler that removes the product in the cart
+ */
+function uc_event_registration_webform_submission_delete_form_submit($form, &$form_state) {  
+  $cart_item = uc_event_registration_get_cart_item_from_sid ($form_state['values']['details']['sid']);  
+  if ($cart_item) {
+    uc_cart_remove_item ($cart_item->nid, $cart_item->cart_id, $cart_item->data);  
+  }
+}
+
+/** 
+ * Implementation of hook_cart_item to remove a webform submission if a paidevent product is removed from the cart (and we are not in the process of creating a proper order)
+ */
+function uc_event_registration_cart_item($op, &$item) {
+  if ($op == 'remove') {
+    $data = unserialize($item->data);
+    // If there is an associated webform submission, delete it
+    if (isset($data['uc_event_registration']['sid'])) {
+      // Remove the webform submission if there are no order products associated with it (if there is an order product, we are probably emptying the cart after creating a proper order)
+      $order_products = uc_event_registration_get_order_products_from_sid($data['uc_event_registration']['sid']);
+      if (empty($order_products)) {
+        $node = node_load($item->nid);
+        if ($node) {
+          module_load_include('inc', 'webform', 'includes/webform.submissions');
+          $submission = webform_get_submission($item->nid, $data['uc_event_registration']['sid']);
+          webform_submission_delete($node, $submission);
+        }
+      }        
+    }      
+  }
+}
+
+/**
+ * Helper function to return cart items that are associated with a webform submission. 
+ * Returns a cart item or an array of cart items depending on the second parameter.
+ * @param $sid_value 
+ *   The webform submission sid
+ * @param $return_first_item_only 
+ *   TRUE - returns the first cart item that matches, FALSE - returns an array of cart items that match
+ */
+function uc_event_registration_get_cart_item_from_sid($sid_value, $return_first_item_only = true) {
+  $items = array();
+  foreach (uc_cart_get_contents() as $item) {
+    if (isset($item->data['uc_event_registration']['sid']) && $item->data['uc_event_registration']['sid'] == $sid_value) {
+      if ($return_first_item_only) {
+        return $item;
+      }
+      else {
+        $items[] = $item;
+      }
+    }
+  }
+  return $items;
+}
+
+/**
+ * Helper function to return the order products associated with a webform submission
+ * @param unknown_type $sid
+ */
+function uc_event_registration_get_order_products_from_sid ($sid) {
+    $sql = <<<SQL
+  SELECT *
+  FROM {uc_event_registration_submissions}
+  WHERE sid = %d
+  ORDER BY order_id DESC
+SQL;
+
+    $oids = array();
+    $res = db_query($sql, $sid);
+    while ($record = db_fetch_array($res)) {
+      $oids[] = $record;
+    }
+    
+    return $oids;
+}
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