michal salaban wrote:

class ObjectRepository:

def getById(self, id): dMain = self.dbpool.runInteraction( fetchOneAndMapToDictionary, "SELECT * FROM MainTable WHERE id = '%d'" % (id,) ) dMain.addCallback(self._gotMainData) return dMain

def _gotMainData(self, mappedRow): dSub = self.dbpool.runInteraction( fetchOneAndMapToDictionary, "SELECT * FROM SubTable WHERE id = '%d'" % (mappedRow['SubID'],) ) dSub.addCallback(self._gotSubData) return [what to return ????]

how can i return the result that consist of data from both queries? chaining callbacks is impossible. i cannot have dSub before dMain.callback() is called, and also cannot do dMain.chainDeferred(dSub) in _gotMainData() because dMain has already been returned to calling code and contains callbacks attached there.

Give this a try and see how it works for you... def _gotMainData(self, mappedRow): dSub = self.dbpool.runInteraction( fetchOneAndMapToDictionary, "SELECT * FROM SubTable WHERE id = '%d'" % (mappedRow['SubID'],) ) dSub.addCallback(self._gotSubData, mappedRow) return dSub def _gotSubData(self, subMappedRow, mainMappedRow): # Do work here. When adding callbacks to a deferred, you can add arguments that will get passed to the argument, independant of the result from previous callbacks. Like above, you can take the mappedRow dictionary from the first callback and pass it as an argument to the callback for the subrequest. Also, for the new deferred to be useful, you return it from the callback. When Twisted sees that, it'll pause the callback chain until that deferred fires and processes all of its callbacks. It'll take the result that is produced from that deferred and use it as the result for the next callback in the main deferred. -- Jason Fritcher Software Engineer Core Infrastructure Services & Strategy Earthlink, Inc fritcher@corp.earthlink.net (404) 748-7262, x22262

michal salaban wrote:

class ObjectRepository:

def getById(self, id): dMain = self.dbpool.runInteraction( fetchOneAndMapToDictionary, "SELECT * FROM MainTable WHERE id = '%d'" % (id,) ) dMain.addCallback(self._gotMainData) return dMain

def _gotMainData(self, mappedRow): dSub = self.dbpool.runInteraction( fetchOneAndMapToDictionary, "SELECT * FROM SubTable WHERE id = '%d'" % (mappedRow['SubID'],) ) dSub.addCallback(self._gotSubData) return [what to return ????]

how can i return the result that consist of data from both queries? chaining callbacks is impossible. i cannot have dSub before dMain.callback() is called, and also cannot do dMain.chainDeferred(dSub) in _gotMainData() because dMain has already been returned to calling code and contains callbacks attached there.

Give this a try and see how it works for you... def _gotMainData(self, mappedRow): dSub = self.dbpool.runInteraction( fetchOneAndMapToDictionary, "SELECT * FROM SubTable WHERE id = '%d'" % (mappedRow['SubID'],) ) dSub.addCallback(self._gotSubData, mappedRow) return dSub def _gotSubData(self, subMappedRow, mainMappedRow): # Do work here. When adding callbacks to a deferred, you can add arguments that will get passed to the argument, independant of the result from previous callbacks. Like above, you can take the mappedRow dictionary from the first callback and pass it as an argument to the callback for the subrequest. Also, for the new deferred to be useful, you return it from the callback. When Twisted sees that, it'll pause the callback chain until that deferred fires and processes all of its callbacks. It'll take the result that is produced from that deferred and use it as the result for the next callback in the main deferred. -- Jason Fritcher Software Engineer Core Infrastructure Services & Strategy Earthlink, Inc fritcher@corp.earthlink.net (404) 748-7262, x22262