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Qt-solutions Archive, January 2007
issues about QTextCodec, UTF-8 and databases

Message 1 in thread

Hi,

I've encoutered a strange behaviour with the Qt 3.3.7 database-classes and 
MySQL 4.1.13 in conjunction with UTF-8.

I defined a table like this:

CREATE TABLE `program` (
  `id` int(11) NOT NULL auto_increment,
  `data` longblob,
  `name` text collate utf8_unicode_ci,
  PRIMARY KEY  (`id`)
) ENGINE=MyISAM DEFAULT CHARSET=utf8 COLLATE=utf8_unicode_ci;


First thing the application does is to set a codec for CStrings (utf8 is 
required for a few other purposes).

   QTextCodec::setCodecForCStrings(QTextCodec::codecForName( "utf8" ));

Then I want to update the database longblob "data" with some binary data.

   QByteArray binaryData = f.readAll();
   // binaryData = qCompress(binaryData);

   QSqlQuery q;

   if (!q.prepare( "UPDATE program SET data = ? WHERE id = ?"))
   {
      qDebug(
         "unable to prepare update-query: '%s'", 
         q.lastError().text().latin1()
      );

      return 1;
   }

   q.bindValue(0, binaryData);
   q.bindValue(1, 123);

   if (!q.exec())
   {
      qDebug(
         "unable to execute update-query: '%s'", 
         q.lastError().text().latin1());

      return 1;
   }

When the query is being executed MySQL throws the following error:

unable to execute update-query: 'You have an error in your SQL syntax; check 
the manual that corresponds to your MySQL server version for the right syntax 
to use near '??_??????S??\Z@??#â??*%8     Q????cE??????-{??\n??????E??
\Z\ZV??W?e??????(??+ixSx=%??E??[????t(????\\' at line 1 QMYSQL3: Unable to 
execute query'

Obviously MySQL doesn't come along with the blob-data sent within the query.

When I remove the "QTextCodec::setCodecForCStrings(...)" command, the query is 
executed without whining.

In the Qt-interest Archive I found the following article
http://lists.trolltech.com/qt-interest/2006-02/thread01317-0.html
suggesting to patch the qt-mysql-driver.

Therefore I added the following line to the open-function of qsql_mysql.cpp 
(Qt 3.3.7 version looks a little different):

mysql_set_character_set(d->mysql, "utf8");

Unfortunately that change had no effect.

Finally I wonder about the following lines within the function 
QMYSQLDriver::hasFeature(...)

    case Unicode:
        return FALSE;

Is there no Unicode-support at all?

Do you have any idea why QTextCodec::setCodecForCStrings may mess around in 
QByteArrays?

Thanks in advance!

- Matthias


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Message 2 in thread

Hi,

> I've encoutered a strange behaviour with the Qt 3.3.7 database-classes and 
> MySQL 4.1.13 in conjunction with UTF-8.

This is a mailing list about Qt Solutions:
     http://www.trolltech.com/products/qt/addon/solutions

For questions about Qt, I would suggest trying qt-interest@:
     http://lists.trolltech.com/qt-interest/

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