在Jquery Symfony Forms中获取当前CollectionType行的元素

I wanna set value one of the field by jquery. Get Value from on field and set it to another field. Got something like this:

$(document).on("click", "a.order_products-collection-rescue-add", function({
    $(".chosen-select").chosen();
    var $product_search = $('order_product');
    $product_search.change(
        function() {
            var single_price  = $(this).find('option.single_option:selected').attr('single_price');
            $(CURENT INDEX OF COLLECTION ROW).('input.single-price-field').val(single_price);
            console.log(this);
        }
    );
});

Everything works fine, but! How i can get Curent Index of Collection Row ? If I click resecue-add button thats embbed my a new form im getting attr single_price from selected option and in new form is second field with class single-price-field, how to get exaclly this form filed ? i dont know how to get index of this form.

$(document).on("click", "a.order_products-collection-rescue-add", function() {
  $(".chosen-select").chosen();

  var $product_search = $('select.order_product');
  $product_search.change(
    function() {
      var single_price = $(this).find('option.single_option:selected').attr('single_price');
      var product_row = $(this).parent().parent().parent();
      $(product_row).find('input.single-price-field').val(single_price);

    }
  );
});