Employee Benefit Application - validate duplicate
diff --git a/erpnext/hr/doctype/employee_benefit_application/employee_benefit_application.py b/erpnext/hr/doctype/employee_benefit_application/employee_benefit_application.py
index 9282d98..f409a13 100644
--- a/erpnext/hr/doctype/employee_benefit_application/employee_benefit_application.py
+++ b/erpnext/hr/doctype/employee_benefit_application/employee_benefit_application.py
@@ -4,7 +4,21 @@
 
 from __future__ import unicode_literals
 import frappe
+from frappe import _
 from frappe.model.document import Document
 
 class EmployeeBenefitApplication(Document):
-	pass
+	def before_submit(self):
+		self.validate_duplicate_on_payroll_period()
+
+	def validate_duplicate_on_payroll_period(self):
+		application = frappe.db.exists(
+			"Employee Benefit Application",
+			{
+				'employee': self.employee,
+				'payroll_period': self.payroll_period,
+				'docstatus': 1
+			}
+		)
+		if application:
+			frappe.throw(_("Employee {0} already submited an apllication {1} for the payroll period {2}").format(self.employee, application, self.payroll_period))