Add extra filter criteria from a separate form

dnagirl

I have a vanilla DataTable based on a Doctrine entity Chemical:

$(document).ready(function() {
    $('#chemical).DataTable( {
        "processing": true,
        "serverSide": true,
        "ajax": ""/CIR/web/app_dev.php/chemical/filter"
    } );
} );

The entity is linked to many other entities that don't need to be displayed in the table. But they would be extremely useful for limiting the result-set. For example, a user may wish to see only those Chemicals that have Supplies which have Items. For overhead reasons, I'd prefer not to include these other entities in a query unless I have to.

What I'd like to do is modify the request parameters that Datatables sends by including the field values from a separate form.

Can I set option ajax = function(){ }? What is passed to the function? Is there a preferred way of modifying Datatables request parameters?