[IMP] base_user_role: UX improvements

base_user_role/models/role.py

@@ -96,6 +96,13 @@ class ResUsersRoleLine(models.Model):
     date_from = fields.Date("From")
     date_to = fields.Date("To")
     is_enabled = fields.Boolean("Enabled", compute="_compute_is_enabled")
+    _sql_constraints = [
+        (
+            "user_role_uniq",
+            "unique (user_id,role_id)",
+            "Roles can be assigned to a user only once at a time",
+        )
+    ]
 
     @api.depends("date_from", "date_to")
     def _compute_is_enabled(self):