How to order the link field in the dialog box

Hi,
I like to order the link field in a dialog box based on another field.I have tried as follows. But it is not working

var dialog = new frappe.ui.Dialog({
		title: __("abc"),
		fields: [
			{
				"fieldtype" : "Link", 
				"options" 	: "box",
				"value" 	: id,
				"label" 	: __("Donation Box"),
				"fieldname" : "don_box",
			},
			{
				"fieldtype" : "Link",
				"reqd" 		: 1,
				"options" 	: "Box Location",
				"filters"    : {"status":"unassigned"},
				"label" 	: __("Select Location"),
				"fieldname":"box_loc",
				"order by" : "asc"
			},
			{"fieldtype":"Button", 	"label": __("Assign"), 	"fieldname": "assign"},
		]
	});

Please help me to fix this problem

Thanks