在python中从数据库中实时获取数据

Question

我有一个Python中的多处理类，它创建了3个不同的进程。第一个过程是检查是否有来自我的硬件的信号，并将其推送到队列中，第二个过程是将数据从队列中取出并推送到数据库中，第三个过程是从数据库中取出数据并推送到服务器上。

obj = QE()
stdFunct = standardFunctions()
watchDogProcess = multiprocessing.Process(target=obj.watchDog)
watchDogProcess.start()

pushToDBSProcess = multiprocessing.Process(target=obj.pushToDBS)
pushToDBSProcess.start()

pushToCloud = multiprocessing.Process(target=stdFunct.uploadCycleTime)
pushToCloud.start()

watchDogProcess.join()
pushToDBSProcess.join()
pushToCloud.join()

我的前两个进程运行得很理想，但我在第三个进程中遇到了困难。以下是我的第三个过程的代码：

def uploadCycleTime(self):
while True:
uploadCycles = []
lastUpPointer = "SELECT id FROM lastUploaded"
lastUpPointer = self.dbFetchone(lastUpPointer)
lastUpPointer = lastUpPointer[0]
# print("lastUploaded :"+str(lastUpPointer))
cyclesToUploadSQL = "SELECT id,machineId,startDateTime,endDateTime,type FROM cycletimes WHERE id > "+str(lastUpPointer)
cyclesToUpload = self.dbfetchMany(cyclesToUploadSQL,15)
cyclesUploadLength = len(cyclesToUpload)
if(cyclesUploadLength>0):
for cycles in cyclesToUpload:
uploadCycles.append({"dataId":cycles[0],"machineId":cycles[1],"startDateTime":cycles[2].strftime('%Y-%m-%d %H:%M:%S.%f'),"endDateTime":cycles[3].strftime('%Y-%m-%d %H:%M:%S.%f'),"type":cycles[4]})        
# print("length : "+str(cyclesUploadLength))
lastUpPointer = uploadCycles[cyclesUploadLength-1]["dataId"]

uploadCycles = json.dumps(uploadCycles)
api = self.dalUrl+"/cycle-times"
uploadResponse = self.callPostAPI(api,str(uploadCycles))
print(lastUpPointer)
changePointerSQL = "UPDATE lastUploaded SET id="+str(lastUpPointer)
try:
changePointerSQL = self.dbAbstraction(changePointerSQL)
except Exception as errorPointer:
print("Pointer change Error : "+str(errorPointer))
time.sleep(2)

现在我保存了一个指针来记住上次上传的id，然后继续上传15个数据包。当数据库中存在数据时，代码运行良好，但如果在启动进程时不存在数据，并且随后发送数据，则无法从数据库中获取数据。

我尝试实时打印长度，它一直给我0，尽管数据不断实时推送到数据库中。

Answer 1

在上传过程中，我错过了一个commit((

def dbFetchAll(self,dataString):
# dataToPush = self.cycletimeQueue.get()
# print(dataToPush)
dbTry = 1
try:
while(dbTry == 1): # This while is to ensure the data has been pushed
sql = dataString
self.conn.execute(sql)
response = self.conn.fetchall()
dbTry = 0
return response
# print(self.conn.rowcount, "record inserted.")
except Exception as error:
print ("Error : "+str(error))
return dbTry
***finally:
self.mydb.commit()***