How to pass parent object's id along with my serialised sortable items?

I've got an Ajax call from the stop event of my jQuery UI sortable that currently looks like this:

...
stop:function(event, ui) {
    $.ajax({
        type: "POST",
        url: "<?php echo site_url('messages/reorder'); ?>",
        data: $("#messagelist").sortable("serialize")
    });
...

Now, that's fine, and it's working (messages/re开发者_Python百科order is a server-side Ajax function that updates the database based on the serialised IDs.)

However, I have multiple lists I could be editing from this page, and I need to pass along the ID of the "parent" object of the list, too.

Is there a standard way of doing this? I know the ID server-side when generating the page. Is there a best-practice way of adding the ID to the "data" that's passed along in my Ajax call?

Sorry if I'm missing something obvious; I'm fairly new to jQuery and Javascript and entirely new to "sortable"...

I ended up doing this by the simple expedient of:

data: "parent_id=" + p_id + "&" + $("#messagelist tbody").sortable("serialize")