use flush, refresh and rollback instead of intemediate commit statements

web/app/services/views.py

@@ -51,13 +51,13 @@ def service(service):
                   service_version=form.version.data,
                   status='preparing', title=form.title.data)
         db.session.add(job)
-        db.session.commit()
+        db.session.flush()
+        db.session.refresh(job)
         try:
             os.makedirs(job.path)
         except OSError:
             logging.error('Make dir {} led to an OSError!'.format(job.path))
-            db.session.delete(job)
-            db.session.commit()
+            db.session.rollback()
             flash('Internal Server Error', 'error')
             return make_response(
                 {'redirect_url': url_for('.service', service=service)}, 500)