no -ve balance accepted in sales and purchase invoice

controllers/accounts_controller.py

@@ -21,6 +21,10 @@ from webnotes.utils import flt
 from utilities.transaction_base import TransactionBase
 
 class AccountsController(TransactionBase):
+	def validate(self):
+		if self.meta.get_field("grand_total"):
+			self.validate_value("grand_total", ">=", 0)
+
 	def get_gl_dict(self, args, cancel=None):
 		"""this method populates the common properties of a gl entry record"""
 		if cancel is None:

controllers/buying_controller.py

@@ -28,6 +28,7 @@ from controllers.accounts_controller import AccountsController
 
 class BuyingController(AccountsController):
 	def validate(self):
+		super(BuyingController, self).validate()
 		if self.meta.get_field("currency"):
 			self.company_currency = get_company_currency(self.doc.company)
 			self.validate_conversion_rate("currency", "conversion_rate")

controllers/selling_controller.py

@@ -23,6 +23,7 @@ from controllers.accounts_controller import AccountsController
 
 class SellingController(AccountsController):
 	def validate(self):
+		super(SellingController, self).validate()
 		self.set_total_in_words()
 		
 	def set_total_in_words(self):