How can I check the connection in python?
I am doing a project reading an RFID tag using python on a raspberry pi and using an RDM880 reader.
My idea is to take the time and time to check the work of the staff on time or not.
I am trying to add card_ID, time_in, time_out to local mysql and remote mysql (IP: 192.168.137.1) using python.
It has the same table in remote and local mysql.
If the mysql remote is corrupted, I only want to add the local mysql.
Here is my code:
import serial
import time
import RPi.GPIO as GPIO
import MySQLdb
from datetime import datetime
from binascii import hexlify
serial=serial.Serial("/dev/ttyAMA0",
baudrate=9600,
parity=serial.PARITY_NONE,
stopbits=serial.STOPBITS_ONE,
bytesize=serial.EIGHTBITS,
timeout=0.1)
db_local = MySQLdb.connect("localhost","root","root","luan_van") #connect local
db = MySQLdb.connect("192.168.137.1", "root_a","","luan_van") #connect remote
ID_rong = 128187 # reader respone if no card
chuoi= "\xAA\x00\x03\x25\x26\x00\x00\xBB"
def RFID(str): #function read RFID via uart
serial.write(chuoi)
data = serial.readline()
tach_5 = data[5]
tach_6 = data[6]
hex_5 = hexlify(tach_5)
hex_6= hexlify(tach_6)
num_5 = int(hex_5,16)
num_6 = int(hex_6,16)
num_a = num_5 * 1000 + num_6
if(num_a != ID_rong):
tach_7 = data[7]
tach_8 = data[7]
hex_7 = hexlify(tach_7)
hex_8= hexlify(tach_8)
num_7 = int(hex_7,16)
num_8 = int(hex_8,16)
num = num_8 + num_7 * 1000 + num_6 * 1000000 + num_5 * 1000000000
else:
num = num_5 * 1000 + num_6
return num
def add_database(): # add card_ID and time_in to remote mysql
with db:
cur = db.cursor()
cur.execure("INSERT INTO tt_control(Card_ID,Time_in) VALUES ('%d',NOW()) " %num)
return
def add_database_local(): # add card_ID and time_in to remote mysql
with db_local:
cur = db_local.cursor()
cur.execure("INSERT INTO tt_control(Card_ID,Time_in) VALUES ('%d',NOW()) " %num)
return
def have_ID(int): #check ID in table tt_control
with db_local:
cur = db_local.cursor(MySQLdb.cursors.DictCursor)
cur.execute("SELECT * FROM tt_control WHERE Card_ID = '%d'" %num)
rows = cur.fetchall()
ID=""
for row in rows:
ID = row['Card_ID']
return ID
def add_time_out(): #add time out to remote mysql
with db:
cur = db.cursor(MySQLdb.cursors.DictCursor)
cur.execute("UPDATE tt_control SET Time_out = NOW() WHERE Card_ID = '%d'" %num)
return
def add_time_out_local(): #add time out to local mysql
with db_local:
cur = db_local.cursor(MySQLdb.cursors.DictCursor)
cur.execute("UPDATE tt_control SET Time_out = NOW() WHERE Card_ID = '%d'" %num)
return
def add_OUT(): #increase Card_ID to distinguish second check
with db:
cur = db.cursor(MySQLdb.cursors.DictCursor)
cur.execute("UPDATE tt_control SET Card_ID = Card_ID + 1 WHERE Card_ID = '%d'" %num)
return
def add_OUT_local(): #increase Card_ID to distinguish second check
with db_local:
cur = db_local.cursor(MySQLdb.cursors.DictCursor)
cur.execute("UPDATE tt_control SET Card_ID = Card_ID + 1 WHERE Card_ID = '%d'" %num)
return
while 1:
num = RFID(chuoi)
time.sleep(1)
Have_ID =have_ID(num)
if(num != ID_rong):
if(Have_ID ==""):
add_database() #---> it will error if remote broken, how can i fix it?
add_database_local()
else:
add_time_out() #---> it will error if remote broken, how can i fix it? I think connection alive can fix, but I don't know
add_time_out_local()
add_OUT()
add_OUT_local() #---> it will error if remote broken, how can i fix it?
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You have several options:
(not so good) Ping the server regularly to keep in touch.
(best) Handle MySQLdb exception when calling cur.execute by re-establishing the connection and calling again. Here's a great and concise answer on how to do it . From this article, you handle the exception yourself:
def __execute_sql(self,sql,cursor):
try:
cursor.execute(sql)
return 1
except MySQLdb.OperationalError, e:
if e[0] == 2006:
self.logger.do_logging('info','DB', "%s : Restarting db" %(e))
self.start_database()
return 0
(finally) Establish a new database connection just before you actually call the database records. In this case, move the definition db
and db_local
in the function you call just before cursor
. If you make thousands of requests, this is not the best. However, if these are just a few queries to the database, it might be a good thing.
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I used a simple technique. Initially, I connected to the DB using:
conect = mysql.connector.connect(host=DB_HOST, user=DB_USER, password=DB_PASS, database=DB_NAME)
Whenever I need to check if the DB is connected, I used the line:
conect.ping(reconnect=True, attempts=3, delay=2)
This will check if the DB connection is alive. If not, it will restart the connection, which will fix the problem.
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