Qt-interest Archive, January 2008
General QSqlDatabase connection questions
Message 1 in thread
disclamer: I am very new to the Qt API.
I've found that I can connect to a PostgreSQL database just fine.
Query it, work with data...etc. No Problem.
The problem I'm looking to gracefully deal with is when a connection is
suddenly and unexpectedly disconnected.
For example, if I pull the ethernet cable after a connection is made.
In this scenario, after the connection is made and isOpen() says yes, I yank
the ethernet cable - .isOpen() continues to say yes.
Additionally, if I submit a query via .exec(Qstring), it just hangs. Maybe it
would timeout eventually - I've only waited 3 minutes.
I've tried db->setConnectOptions("connect_timeout=10;"); as described here:
http://doc.trolltech.com/4.2/qsqldatabase.html#setConnectOptions
But...
1 - that doesn't cause connection to timeout after 10 seconds, as I suspect it
should.
2 - that parameter refers to connections, not executions of queries.
So:
Why does connect_timeout=10 as a connection option not set the connection
timeout to 10 seconds?
What is the preferred method for testing an established connection?
How can I make an exec timeout a little faster?
Thanks
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Message 2 in thread
Rick Vernam wrote:
> disclamer: I am very new to the Qt API.
>
> I've found that I can connect to a PostgreSQL database just fine.
> Query it, work with data...etc. No Problem.
>
> The problem I'm looking to gracefully deal with is when a connection is
> suddenly and unexpectedly disconnected.
> For example, if I pull the ethernet cable after a connection is made.
> In this scenario, after the connection is made and isOpen() says yes, I yank
> the ethernet cable - .isOpen() continues to say yes.
> Additionally, if I submit a query via .exec(Qstring), it just hangs. Maybe it
> would timeout eventually - I've only waited 3 minutes.
>
> I've tried db->setConnectOptions("connect_timeout=10;"); as described here:
> http://doc.trolltech.com/4.2/qsqldatabase.html#setConnectOptions
> But...
> 1 - that doesn't cause connection to timeout after 10 seconds, as I suspect it
> should.
> 2 - that parameter refers to connections, not executions of queries.
>
> So:
> Why does connect_timeout=10 as a connection option not set the connection
> timeout to 10 seconds?
> What is the preferred method for testing an established connection?
> How can I make an exec timeout a little faster?
>
> Thanks
>
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Are you using setConnectOptions before you open the connection? It has
no effect if you use it on an open connection. A simple thing but I have
to ask :) Also, I believe that connect_timeout only applies to the
actual connection phase of your database session (i.e. when you call
db->open()).
As for checking the connection, there doesn't seem to be a pretty way to
do that... if you can afford the overhead and it is critical that you
know if the connection is open, you may just want to re-open the
connection before executing a query.
Hope that helps,
Stuart
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