Save the form on change of a child table

1

How can I save the parent form if I change a field of child table?

2 
frappe.ui.form.on('Child Table Name', {
    item_name: function(frm, cdt, cdn) {
        cur_frm.save();
    }
});

by the way, it’s not a good solution to save form each time you change any field!

3

and how can we test that this field is not empty?

5

check bellow:

 frappe.ui.form.on('Child Table Name', {
        item_name: function(frm, cdt, cdn) {
    	    var row = locals[cdt][cdn];
    	    if(row.item_name){
    	    	cur_frm.save();
    	    }
        }
    });