Hi! In the application I'm currently working on, we gather data from different sources and store them in a database, but only if the values have changed.
One example is GPS information. We don't want to store hundreds of identical values that are sent by the receiver, so we have to compare the last written row with the current latitude / longitude pair. I use a subclass of NMEARreceiver class to determine the current latitude and longitude. Then I query the database using a ConnectionPool instance to get the previous values for latitude and longitude. If the result differs from the current values, a new entry is stored, again using the ConnectionPool. The problem is: How do I "connect" the current latitude and longitude to the database query? The query returns a Deferred object, but this expects a callback with only one argument, the result of the query. Storing them as instance variables of NMEAReceiver does not seem to be the right way, since I don't know how long it takes to query the database - the relevant GPS information might be overwritten by a new NMEA telegram when the connection pool finally triggers the callback One workaround I've found is to add this information to the SQL query, but this seems quite weird to me (and doesn't work in the case that the query does not return a result). A different approach would be to implement a callback with three arguments (result, latitude and longitude), and wrap it in a lambda function that fills latitude and longitude with the current values. Would this would be a better way to handle this requirement? How would you implement this? Thanks & best regards, Albert -- Albert Brandl Weiermayer Solutions GmbH | Abteistraße 12, A-4813 Altmünster phone: +43 (0) 720 70 30 14 | fax: +43 (0) 7612 20 3 56 web: http://www.weiermayer.com _______________________________________________ Twisted-Python mailing list Twisted-Python@twistedmatrix.com http://twistedmatrix.com/cgi-bin/mailman/listinfo/twisted-python
