Quotation calculate price list rate total

Hi everybody;
H need to show total price before adding discount
so i created a custom field “total before discount” which just will be total of all items price list rates, I made this custom script for automatically make this calculation but not working
total before discount always =0 why?

     `frappe.ui.form.on('Quotation',"price_list_rate", {
      validate: function(frm) {
	  total_qty = 0;
	  $.each(frm.doc.items || [], function(i, d) {
		total_qty +=flt(d.price_list_rate);
	  });
	  frm.doc.total_before_discount=total_qty;
	  frm.refresh_fields();
}}); 

`

you cannot assign value to a field using ‘=’,
use

frm.set_value("field_name","value")

also not working it still 0

frappe.ui.form.on('Quotation',"price_list_rate", {
validate: function(frm) {
	total_qty = 0;
	$.each(frm.doc.items || [], function(i, d) {
		total_qty +=flt(d.price_list_rate);
	});
	frm.set_value('total_before_discount',total_qty);
	frm.refresh_fields();
}

});

check & see if the value is actually getting computed and stored in total_qty in each iteration by printing it to console or something


so what does that mean?

correct this to your appropriate trigger,

frappe.ui.form.on('Job Card Entry',{validate :function(frm){

it works now thanks so much