brotherton-erpnext/erpnext/patches/v11_0/move_leave_approvers_from_employee.py

import frappe
from frappe import _
from frappe.model.utils.rename_field import rename_field

def execute():
	frappe.reload_doc("hr", "doctype", "department_approver")
	frappe.reload_doc("hr", "doctype", "employee")
	frappe.reload_doc("hr", "doctype", "department")

	if frappe.db.has_column('Department', 'leave_approver'):
		rename_field('Department', "leave_approver", "leave_approvers")

	if frappe.db.has_column('Department', 'expense_approver'):
		rename_field('Department', "expense_approver", "expense_approvers")

	if not frappe.db.table_exists("Employee Leave Approver"):
		return

	approvers = frappe.db.sql("""select distinct app.leave_approver, emp.department from
	`tabEmployee Leave Approver` app, `tabEmployee` emp
		where app.parenttype = 'Employee'
		and emp.name = app.parent
		""", as_dict=True)

	for record in approvers:
		if record.department:
			department = frappe.get_doc("Department", record.department)
			if not department:
				return
			if not len(department.leave_approvers):
				department.append("leave_approvers",{
					"approver": record.leave_approver
				}).db_insert()