การใช้เงื่อนไข Where โดยใช้ภาษา LINQ กับ Entity Framework

string sql = " Select * from customer " ;
if(radio_id.checked == true)
{
sql += "Where id_no = '+ txt_box.Text +'" ;
}
else if(radio_name.checked == true)
{
sql += "Where name = '+ txt_box.Text +'" ;

}

var ds = (from c in db.customer
	select c);
if(radio_id.checked == true)
{
	ds = ds.Where(o => (o.id_no == txt_box.Text));
}
else if(radio_name.checked == true)
{
	ds = ds.Where(o => (o.name == txt_box.Text));
}

var ds = (from c in db.customer
	select c);
if(radio_id.checked == true)
{
	ds = ds.Where(o => (o.id_no == txt_box.Text));
}
else if(radio_name.checked == true)
{
	ds = ds.Where(o => (o.name == txt_box.Text));
}

var ds = (from c in db.customer
where c.id_no = (radio_id.checked ? txt_box.text : c.id_no) and c.name = (radio_name.checked() ? txt_name.text : c.name)
	select c).toList();