diff --git a/tracsubtickets/api.py b/tracsubtickets/api.py
index 35fbed7..7818b1f 100644
--- a/tracsubtickets/api.py
+++ b/tracsubtickets/api.py
@@ -47,7 +47,7 @@
 
 # i18n support for plugins, available since Trac r7705
 # use _, tag_ and N_ as usual, e.g. _("this is a message text")
-_, tag_, N_, add_domain = domain_functions('tracsubtickets', 
+_, tag_, N_, add_domain = domain_functions('tracsubtickets',
     '_', 'tag_', 'N_', 'add_domain')
 
 
@@ -71,8 +71,7 @@ def environment_created(self):
 
     def environment_needs_upgrade(self, db):
         cursor = db.cursor()
-        cursor.execute("SELECT value FROM system WHERE name=%s",
-                       (db_default.name, ))
+        cursor.execute("SELECT value FROM system WHERE name=%s", (db_default.name, ))
         value = cursor.fetchone()
         try:
             self.found_db_version = int(value[0])
@@ -95,17 +94,15 @@ def upgrade_environment(self, db):
         old_data = {} # {table.name: (cols, rows)}
         cursor = db.cursor()
         if not self.found_db_version:
-            cursor.execute("INSERT INTO system (name, value) VALUES (%s, %s)",
-                           (db_default.name, db_default.version))
+            cursor.execute("INSERT INTO system (name, value) VALUES (%s, %s)", (db_default.name, db_default.version))
         else:
-            cursor.execute("UPDATE system SET value=%s WHERE name=%s",
-                           (db_default.version, db_default.name))
+            cursor.execute("UPDATE system SET value=%s WHERE name=%s", (db_default.version, db_default.name))
             for table in db_default.tables:
                 cursor.execute("SELECT * FROM %s", (table.name, ))
                 cols = [x[0] for x in cursor.description],
                 rows = cursor.fetchall()
                 old_data[table.name] = (cols, rows)
-                cursor.execute("DROP TABLE %s", (table.name))
+                cursor.execute("DROP TABLE %s", (table.name, ))
 
         # insert the default table
         for table in db_default.tables:
@@ -132,13 +129,15 @@ def ticket_created(self, ticket):
         self.ticket_changed(ticket, '', ticket['reporter'], {'parents': ''})
 
     def ticket_changed(self, ticket, comment, author, old_values):
+        self.log.debug("Ticket changed. Ticket id: %s" % ticket.id)
         if 'parents' not in old_values:
             return
 
         old_parents = old_values.get('parents', '') or ''
         old_parents = set(NUMBERS_RE.findall(old_parents))
         new_parents = set(NUMBERS_RE.findall(ticket['parents'] or ''))
-
+        self.log.debug("Old parents: %s" % old_parents)
+        self.log.debug("New parents: %s" % new_parents)
         if new_parents == old_parents:
             return
 
@@ -147,19 +146,18 @@ def ticket_changed(self, ticket, comment, author, old_values):
 
         # remove old parents
         for parent in old_parents - new_parents:
-            cursor.execute("DELETE FROM subtickets WHERE parent=%s AND child=%s",
-                           (parent, ticket.id))
+            cursor.execute("DELETE FROM subtickets WHERE parent = %s AND child = %s", [str(parent), str(ticket.id)] )
+
         # add new parents
         for parent in new_parents - old_parents:
-            cursor.execute("INSERT INTO subtickets VALUES(%s, %s)",
-                           (parent, ticket.id))
+            cursor.execute("INSERT INTO subtickets VALUES(%s, %s)", (parent, ticket.id))
         db.commit()
 
     def ticket_deleted(self, ticket):
         db = self.env.get_db_cnx()
         cursor = db.cursor()
         # TODO: check if there's any child ticket
-        cursor.execute("DELETE FROM subtickets WHERE child=%s", (ticket.id, ))
+        cursor.execute("DELETE FROM subtickets WHERE child=%s", [str(ticket.id)])
         db.commit()
 
     # ITicketManipulator methods
@@ -189,7 +187,7 @@ def validate_ticket(self, req, ticket):
             def _check_parents(id, all_parents):
                 all_parents = all_parents + [id]
                 errors = []
-                cursor.execute("SELECT parent FROM subtickets WHERE child=%s", (id, ))
+                cursor.execute("SELECT parent FROM subtickets WHERE child=%s", [str(id)])
                 for x in [int(x[0]) for x in cursor]:
                     if x in all_parents:
                         error = ' > '.join(['#%s' % n for n in all_parents + [x]])
diff --git a/tracsubtickets/web_ui.py b/tracsubtickets/web_ui.py
index 3b33175..968398c 100644
--- a/tracsubtickets/web_ui.py
+++ b/tracsubtickets/web_ui.py
@@ -37,9 +37,7 @@
 
 from api import NUMBERS_RE, _
 
-
 class SubTicketsModule(Component):
-
     implements(ITemplateProvider,
                IRequestFilter,
                ITicketManipulator,
@@ -94,12 +92,13 @@ def prepare_ticket(self, req, ticket, fields, actions):
         pass
 
     def get_children(self, parent_id, db=None):
+        self.log.debug("Get children for parent: %s" % parent_id)
         children = {}
         if not db:
             db = self.env.get_db_cnx()
+
         cursor = db.cursor()
-        cursor.execute("SELECT parent, child FROM subtickets WHERE parent=%s",
-                       (parent_id, ))
+        cursor.execute("SELECT parent, child FROM subtickets WHERE parent=%s", [str(parent_id)] )
 
         for parent, child in cursor:
             children[child] = None
@@ -108,15 +107,13 @@ def get_children(self, parent_id, db=None):
             children[id] = self.get_children(id, db)
 
         return children
-        
+
     def validate_ticket(self, req, ticket):
         action = req.args.get('action')
         if action == 'resolve':
             db = self.env.get_db_cnx()
             cursor = db.cursor()
-
-            cursor.execute("SELECT parent, child FROM subtickets WHERE parent=%s",
-                           (ticket.id, ))
+            cursor.execute("SELECT parent, child FROM subtickets WHERE parent=%s", [str(ticket.id)] )
 
             for parent, child in cursor:
                 if Ticket(self.env, child)['status'] != 'closed':