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Query/fetch don't return result when it *theorically* should

Bernard Lebel 3dbernard at gmail.com
Wed Jan 18 17:48:58 EST 2006 
Hi Alan,

On 1/18/06, Alan Franzoni <alan.franzoni.xyz at gmail.com> wrote:
> Il Wed, 18 Jan 2006 14:39:09 -0500, Bernard Lebel ha scritto:
> 1) It would be great if you didn't post four messages in less than an hour
> ^_^

Yeah I know :-)
But like I said, I've been stuck for 3 days on that, so, I need to get
things off my chest. Sorry to anyone that got a smell of spam :-)


> 2) Your code is very long! You can't expect many people to run and read it
> all! You should post a very small demo program with the very same problem
> as your main software. It'll help us a lot.

Okay thanks for the advice. I have done what you have suggested.


In this first example, I fetch an integer value from the database
table. So far so good. However, if I change this value, the script
keeps printing the same value over and over, eternally. Notic that
everytime the while loop performs an iteration, a new cursor object is
created, as you suggested.

if __name__ == '__main__':
	
	oConnection = MySQLdb.connect( host = '192.168.10.101', user =
'render', passwd = 'rnrender', db = 'RenderFarm_BETA' )
	sQuery = "SELECT LogLevel FROM TB_RENDERNODES WHERE ID = 108"

	while 1:
		
		oCursor = oConnection.cursor()
		oCursor.execute( sQuery )
		oResult = oCursor.fetchone()
		print oResult
		oCursor.close()
		
		print 'waiting 5 seconds'
		time.sleep( 5 )




In the next one, I close the connection and create a new one. At that
point, the script prints the right value when I change it in the
database.


if __name__ == '__main__':
	
	sQuery = "SELECT LogLevel FROM TB_RENDERNODES WHERE ID = 108"

	while 1:
		oConnection = MySQLdb.connect( host = '192.168.10.101', user =
'render', passwd = 'rnrender', db = 'RenderFarm_BETA' )
		oCursor = oConnection.cursor()
		oCursor.execute( sQuery )
		oResult = oCursor.fetchone()
		print oResult
		oCursor.close()
		oConnection.close()
		
		print 'waiting 5 seconds'
		time.sleep( 5 )




So I suspected that it had something to do with the threaded queue,
but I can see it's not, since the examples above are not using it at
all.



Btw I did not expect anyone to run through the code, but just in case
someone spotted something fishy... :-)





> 3) IMHO your problem looks like something related to isolation levels. You
> should check with your DB-adapter docs about the issue. You may need to
> manually sync/commit the connection or the cursor. Instead of re-creating
> the connection, have you tried just creating a new cursor object at every
> query?
>
> If you want to do a quick-test, try any ORM, like sqlalchemy or sqlobject,
> and check the results.


Okay I'll check these out.


Thanks
Bernard
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