# HG changeset patch
# Parent 7a7d003fe38426a405ce0657a627a139133ec4dd
# Parent  52f54b46487c8224a5aade4b921be77360ed3eae

diff --git a/openacademy/models.py b/openacademy/models.py
--- a/openacademy/models.py
+++ b/openacademy/models.py
@@ -1,6 +1,6 @@
 # -*- coding: utf-8 -*-
 
-from openerp import models, fields, api
+from openerp import models, fields, api, exceptions
 
 class Course(models.Model):
     _name = 'openacademy.course'
@@ -56,3 +56,9 @@ class Session(models.Model):
                     'message': "Increase seats or remove excess attendees",
                 },
             }
+
+    @api.constrains('instructor_id', 'attendee_ids')
+    def _check_instructor_not_in_attendees(self):
+        for r in self:
+            if r.instructor_id and r.instructor_id in r.attendee_ids:
+                raise exceptions.ValidationError("A session's instructor can't be an attendee")