How to Notice Close of MySql Server in Qt

Question

When I closed MySql server, how can I understand that mysql server is gone away from my Qt program?

Edit:

Here my trial:

When I close MySql, I get these results, and I can't catch that MySql is closed.

My Code Snippet is

QSqlQuery query(db);
query.exec("SELECT * From RequestIds");
qDebug()<<query.lastError();
qDebug()<<db.lastError()<<QTime::currentTime();
qDebug()<<db.isOpen();
qDebug()<<db.isValid();

and output is:

QSqlError(2006, "QMYSQL: Unable to execute query", "MySQL server has gone away") 
QSqlError(-1, "", "") QTime("14:22:58") 
true 
true

I don't understand why db.isOpen() returns true.

Answer 1

There is a bug related with QSqlDatabase::isOpen() in Qt.

https://bugreports.qt.io/browse/QTBUG-223

Answer 2

Your program has no idea of its surroundings. If something changes, you may be able to have the OS notify your program, or you'll have to test yourself.

If the database connection closes before your program, the status from the connection should return some kind of error code. You are checking status from the connection functions?

Write a simple program that opens a window and upon the click of a button, writes to the database. After writing to the database, the program should display the status in the window. Run your program. Press button to get the "controlled" response. Close the database then click on the button again.

You may be able to do this with a debugger, depending on the ability of the debugger & OS to queue up messages.