[Qt-interest] QtSql - fail to send blob data

[Cyril]

Sure, but that's not the problem. I initialize the field as an empty blob.
Everything looks just as if the driver would not "close the packet" even
though the successive chunks are sent one by one to the mysql server at each
QSqlQuery::exec().
Even enclosing each UPDATE query in an explicit transaction doesn't help.

2011/9/8 Robert Hairgrove <evorgriahr at hispeed.ch>

> On Thu, 2011-09-08 at 16:29 +0200, Cyril wrote:
> > Thanks for your answers.
> > I am using MySQL server 5.5.8, MySQL database driver of Qt 4.7 ,
> > libmysql 6.0.2, under windows 7.
> > I tried the CONCAT syntax using hex-encoded blob but it still fails
> > the same way. Here is the code :
> >
> >
> > {
> >   QSqlQuery q1(db);
> >   q1.prepare("INSERT INTO t (id, data) VALUES(42, '')"); // field data
> > is a LONGBLOB
> >   q1.exec();
> > }
> >
> >
> > QByteArray bigData; // several megabytes of data to insert in DB
> > const int chunkSize = 50000;
> >
> >
> > int i = 0;
> > while(!bigData.isEmpty()) {
> >   QByteArray chunk = bigData.left(chunkSize);
> >   bigData = bigData.mid(chunkSize);
> >
> >
> >   QString str = QString::fromLatin1("UPDATE t SET data=CONCAT(data, 0x
> > %1) WHERE id=42").arg(QString(chunk.toHex()));
> >
> >
> >   QSqlQuery q2(db);
> >   q2.prepare(str);
> >   q2.exec(); //<<<<<< still fails when i==max_allowed_packet/chunkSize
> >
> >
> >   i++;
> > }
> >
> >
> >
> >
> > Note that this technique works fine when using phpmyadmin or any other
> > mysql interactive kind of console, which proves that the BLOB data
> > doesn't get mangled by CONCAT.
> > Anybody has an idea? Bug in QtSql?
>
> What happens if data is NULL on the first update? In that case, CONCAT
> would also return NULL. This is safer:
>
>  QString str = QString::fromLatin1("UPDATE t "
>                  "SET data=CONCAT(COALESCE(data,''), 0x%1) WHERE id=42")
>                 .arg(QString(chunk.toHex()));
>
>
>
> _______________________________________________
> Qt-interest mailing list
> Qt-interest at qt.nokia.com
> http://lists.qt.nokia.com/mailman/listinfo/qt-interest
>
-------------- next part --------------
An HTML attachment was scrubbed...
URL: http://lists.qt-project.org/pipermail/qt-interest-old/attachments/20110908/8b99d104/attachment.html