Qt and MySQL Database Connection

[shamik]

what are these mysql development packages. and tell me how does mysql installation is seen bydefault by the system. what actually d u mean by this. i had tried configuring qt many times as under:
./configure -qt-sql-mysql
./configure -plugin-sql-mysql

but everytime it gave some error during make process. in my pc and other ones too, qt installation takes more than 4hrs of time.

i have already started qt installation and by evening it will get over.
before that i had re-installed mysql but after the installation all the tables, and databases which i had made previously existed in the newer installation also which i think should have got vanished.

i am again planning to do linux installation again and then mysql and then qt

please help me yaar, i am fed up of this stupid things. why does it work in one of the pcs and why not in mine?

[wysota]

what are these mysql development packages.

mysql-devel or simmilar.

and tell me how does mysql installation is seen bydefault by the system. what actually d u mean by this.

I'm sorry, this is a Qt related forum. I don't feel competent enough to answer MySQL related questions. By "seen by default" I meant that the library and header files is visible by the loader/compiler without need to set any environment variables or something like that.

i had tried configuring qt many times as under:
./configure -qt-sql-mysql
./configure -plugin-sql-mysql

It is possible that you should also use -I and -L to point the compile process to appropriate places of your MySQL installation. This is if your MySQL installation is not "seen by default" by your system.

but everytime it gave some error during make process.

If you report the errors here, maybe we'll be able to help solve them. Alternatively use Google and solve them yourself.

in my pc and other ones too, qt installation takes more than 4hrs of time.

That's normal for Qt3. My first own compilation of Qt3 took about 8 hours.

before that i had re-installed mysql but after the installation all the tables, and databases which i had made previously existed in the newer installation also which i think should have got vanished.

Did you do that using some package manager? If so, they should be safe.

i am again planning to do linux installation again and then mysql and then qt

It's not Windows, you don't need to reinstall everything just to get one component to work.

please help me yaar, i am fed up of this stupid things. why does it work in one of the pcs and why not in mine?

You probably use some custom things. Trying to get MySql5 work with qmysql3 is one of them, IMO...

[shamik]

hiii

about the installation , as u were telling it takes around 8hrs wth u, but at my friend's home it takes just 20 mins, he's got fedora 5 but qt version is same. has it got anything to do with processor??

i dint un/installed mysql using any package manager. what i did is just deleted the mysql folder from /usr/local and then again re-installed from the .tar file i had to the same folder /usr/local/mysql.

i dont really setup any environment variables during mysql installation. only that my.cnf gets modified to set up the path of mysql.sock file. nothing else

now what?

[wysota]

has it got anything to do with processor??

Sure, the faster the processor, the shorter the compilation time.

i dint un/installed mysql using any package manager. what i did is just deleted the mysql folder from /usr/local and then again re-installed from the .tar file i had to the same folder /usr/local/mysql.

So you deleted all your databases with it. If you use RedHat (and I think you do), use its package manager (Yast or something like that) to install the software from RPMs. You can install appropriate RPMs manually too. This will save you a lot of trouble.

i dont really setup any environment variables during mysql installation. only that my.cnf gets modified to set up the path of mysql.sock file. nothing else

If you install any software in a custom place (and /usr/local/mysql might be considered one), you should inform your system, that the software is there and that it should look for it there. Otherwise it will be unable to use it.

[shamik]

i have mysql 5 as .tar file so i dont use rpm package manager to install that. and since it doesnt list mysql5 in its package's list i dnt use it either to uninstall also. when i give the command : rpm -qa | grep mysql all it lists is :
mysql-server 3.23.. (..version..)
mysql 3.23
mysql-devel 3.23

and not mysql5.

i have installed mysql in a custom place /usr/local/mysql. tell me how to inform the system about it.
will that solve the relocation error it is giving?

[wysota]

http://unixhelp.ed.ac.uk/CGI/man-cgi?ld.so
http://unixhelp.ed.ac.uk/CGI/man-cgi?ldconfig+8

I don't know if it will solve them, but you surely won't be able to use mysql5 client library without it. Also make sure you compile the qsqlmysql driver against that library.

[shamik]

thanks for the links you provided.

as u suggested i have tried out
$gdb ./designer

i.e. opened qt in debugger. then i tried to make the connection by selecting the QMYSQL3 driver and the clicked connect. as usual qt crashed. but on the shell i got following error:

#$gdb ./designer

QSqlDatabase : driver not loaded
QSqlDatabase : available drivers : QMYSQL3
./designer : relocation error : /usr/local/qt/plugins/sqdrivers/libqsqlmysql.so : undefined symbol : mysql_server_init

from the links you provided i tried out
ldconfig

it did something, (i donno what) and then returned to the shell.

then i tried
ld libqsqlmysql.so
it gives

ld : warning : cannot find entry symbol _start;not setting start address
libqsqlmysql.so : undefined reference to 'mysql_server_init'
libqsqlmysql.so : undefined reference to 'mysql_server_end'

and yes i have tried out what you told about linking to embedded mysql. but i dont have that mysqld.so library with me so i think it would not be the case. of that kind what i only have is mysqld.a file. all the .so files have the initials 'libmysqlclient'.

i think now it would help you to trace out the problem.

[wysota]

Did you add a path to your MySQL5 client library to ld.so.conf before running ldconfig? Did you recompile the driver afterwards?

Maybe you should first try to get QMYSQL3 with MySQL3 up and running? You might be chasing a bug which is caused by something completely different.

[shamik]

i have added the newer qt's library path to ld.so.conf in /etc . the contents of this file are now:

/usr/kerberos/lib
/usr/X11R6/lib
/usr/lib/sane
/usr/local/qt/lib
/usr/lib/mysql

the last two lines i have added. then i did ldconfig (without any options).
then i recomipiled my driver using the qmake and make process as i told u.
and then tested by $gdb ./designer

but everything is same. mainly the error.
actually i did ldconfig -v so that it would list the files it is processing. it showed libmysqlclient.so file in the /lib/mysql folder and the qt lib files also.

"Maybe you should first try to get QMYSQL3 with MySQL3 up and running"

what do you mean by this. i have already QMYSQL3 running on this particular MYSQL5 on one of the pcs and the connection is working fine. but on my pc only it is giving error. so i dont think it is a compatiblity issue.

[shamik]

hii there

i have installed linux, mysql and qt again. as u suggested i installed mysql devel package before installing qt.

everythings working fine. qt which used to crash before is not crashing anymore and the connection is seen and setup fine.

but one more problem has occured.

as i press connect the connection appears on the left side pane. that means the connection is setup. now i have tried to do a simple book's example from the qt manual.

in my mysql i have created a database called "manager" and inside it created a table called "book" and have some values inserted in it.

now (going back to qt) after creating the connections, i clicked on tools-database-datatable.
a data table setup appeared and i did as given in the manual. note that all the columns in the "book" table in mysql were shown after i finished the datatable settings. this means the driver is working fine and all the settings have been correct.

now i had pasted the following code from the manual to my project :

#include<qsqldatabase.h>
#include<qapplication.h>
 
bool createconnections()
{
	QSqlDatabase *db= QSqlDatabase::addDatabase(“QMYSQL3”);
if(!db)
{
	qWarning(“Failed to connect to driver”);
	return FALSE;
}
 
db->setDatabaseName(“manager”);
db->setUserName(“root”);
db->setPassword(“”);
db->setHostName(“localhost”);
 
if(!db->open())
{
	qWarning(“Failed to open books database : “ + db->lastError().driverText());
qWarning(db->lastError().databaseText());
return FALSE;
}
return TRUE;
}
 
int main(int argc, char *argv[])
{
	Qapplication a(argc,argv);
	If(!createconnections())
	{
		return 1;
	}
	BookForm bookForm;
	a.setMainWidget(&bookForm);
	bookForm.show();
	return a.exec();
}

#include<qsqldatabase.h>
#include<qapplication.h>

bool createconnections()
{
	QSqlDatabase *db= QSqlDatabase::addDatabase(“QMYSQL3”);
if(!db)
{
	qWarning(“Failed to connect to driver”);
	return FALSE;
}

db->setDatabaseName(“manager”);
db->setUserName(“root”);
db->setPassword(“”);
db->setHostName(“localhost”);

if(!db->open())
{
	qWarning(“Failed to open books database : “ + db->lastError().driverText());
qWarning(db->lastError().databaseText());
return FALSE;
}
return TRUE;
}

int main(int argc, char *argv[])
{
	Qapplication a(argc,argv);
	If(!createconnections())
	{
		return 1;
	}
	BookForm bookForm;
	a.setMainWidget(&bookForm);
	bookForm.show();
	return a.exec();
}

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please ignore any spelling mistakes or caps mistake in the code as i have typed this manually in windows.

this code compiles well and exe is also formed as usual.

but when i run the exe from the shell it gives following error :

#./book
QSqlDatabase warning : QMYSQL3 driver not loaded
QSqlDatabase : available drivers :
Failed to open books database : Driver not loaded
Driver not loaded


please tell me where am i going wrong.

[wysota]

Do Qt SQL examples work correctly?

[shamik]

sorry, it was 3 days holiday in our country (festivals)

anyways
i dont understand what u mean by "Do Qt SQL examples work correctly?"

the examples are given in the qt manual so i assumed they must be correct.
else can u provide me with a small code so that i can check wheather my connection is working or not.

thanks.

[wysota]

i dont understand what u mean by "Do Qt SQL examples work correctly?"

the examples are given in the qt manual so i assumed they must be correct.

I'm not asking about the code but actual programs residing in examples/ and demos/ directories of your Qt application.

else can u provide me with a small code so that i can check wheather my connection is working or not.

I can't. You have Qt examples for that, that's why I asked you to check if they work I can provide code which is not bound to be correct, whereas Qt examples are correct for sure so everyone checks against them if they can.

[shamik]

ok

the in the other pc, the code which i had provided is working and the exe is running good and shows all the contents of the database.

in my pc, i have tried the same code.
in the qt window when i press preview->preview form

the form with the datatable is shown and all the contents of the actual database in mysql are reflected in the datatable.
but why only when i run the exe nothing is shown. this means there is no problem with the driver as it showing the contents of the database.
there must be something else. what say??
also i have to open the newer version of qt manually.
the kdevelop doesnt take it bydefault. it takes the older version.
is there any setting by which kdevelop can take it automatically.

thanks
shamik

[wysota]

ok

the in the other pc, the code which i had provided is working and the exe is running good and shows all the contents of the database.

in my pc, i have tried the same code.
in the qt window when i press preview->preview form

the form with the datatable is shown and all the contents of the actual database in mysql are reflected in the datatable.
but why only when i run the exe nothing is shown. this means there is no problem with the driver as it showing the contents of the database.
there must be something else. what say??

Please run the SQL examples from Qt3. Don't test your code as it may not be completely valid. Test on something which is known to be valid.

also i have to open the newer version of qt manually.
the kdevelop doesnt take it bydefault. it takes the older version.
is there any setting by which kdevelop can take it automatically.

I don't know what "newer" means in this case. Maybe you didn't install Qt correctly. If you install it in a custom path, you have to make sure $QTDIR and $PATH point to proper places. QTDIR should point to the main directory of Qt3 installation and PATH should contain the place where qmake, uic, moc and other needed binaries are stored (most probably $QTDIR/bin).

[shamik]

ok
now here is something new.

i have made a new project called book.pro
following is the code for it :

bool createConnections()
{
    // create the default database connection
    QSqlDatabase *defaultDB = QSqlDatabase::addDatabase( "QMYSQL3" );
    if ( ! defaultDB )
    {
       qWarning( "Failed to connect to driver" );
        return FALSE;
    }
    defaultDB->setDatabaseName( "mysql" );
    defaultDB->setUserName( "root" );
    defaultDB->setPassword( "" );
    defaultDB->setHostName( "localhost" );
    if ( ! defaultDB->open() ) {
                qWarning( "Failed to open mysql database: " +
                  defaultDB->lastError().driverText() );
        qWarning( defaultDB->lastError().databaseText() );
        return FALSE;
    }    
      	return TRUE;   
}
int main( int argc, char **argv )
{
    QApplication a( argc, argv );
    QDataTable tb(0,"Author Table");
    BookForm w;
    int i=0;
    if ( ! createConnections() )
    {
	i=1;
                return 1;
	qWarning("This is my warning. Error is in createConnection(). i=%d",i);	
     }
 //   w.show();
//    tb.show();
    a.connect( &a, SIGNAL( lastWindowClosed() ), &a, SLOT( quit() ) );
    return a.exec();
}

bool createConnections()
{
    // create the default database connection
    QSqlDatabase *defaultDB = QSqlDatabase::addDatabase( "QMYSQL3" );
    if ( ! defaultDB )
    {
       qWarning( "Failed to connect to driver" );
        return FALSE;
    }
    defaultDB->setDatabaseName( "mysql" );
    defaultDB->setUserName( "root" );
    defaultDB->setPassword( "" );
    defaultDB->setHostName( "localhost" );
    if ( ! defaultDB->open() ) {
                qWarning( "Failed to open mysql database: " +
                  defaultDB->lastError().driverText() );
        qWarning( defaultDB->lastError().databaseText() );
        return FALSE;
    }    
      	return TRUE;   
}
int main( int argc, char **argv )
{
    QApplication a( argc, argv );
    QDataTable tb(0,"Author Table");
    BookForm w;
    int i=0;
    if ( ! createConnections() )
    {
	i=1;
                return 1;
	qWarning("This is my warning. Error is in createConnection(). i=%d",i);	
     }
 //   w.show();
//    tb.show();
    a.connect( &a, SIGNAL( lastWindowClosed() ), &a, SLOT( quit() ) );
    return a.exec();
}

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i have included following header files :
qapplication.h , qsqldatabase.h , qsqlrecord.h , qsqlfield.h , qdatatable.h , "form1.h"

as usual the exe is formed without any errors. u can try it if you want.
in the form i have a qdatatable.
now in mysql bydefault there is a database called "mysql"
i have tried to use that.
while creating qdatatable all the tables in the database "mysql" were listed and i have selected "help_category" table.
inside this table there are various entries already present.

when i preview the form , all the entries are listed as it is.

but when i run the program from the shell the following error comes :


[root@localhost book]# ./book
QSqlCursor::setName: unable to build record, does 'help_category' exist?
QSqlRecord::field: index out of range: 0
QSqlRecord::position: unable to find field name
QSqlRecord::field: index out of range: -1
QSqlRecord::field: index out of range: 1
QSqlRecord::position: unable to find field parent_category_id
QSqlRecord::field: index out of range: -1
QSqlRecord::field: index out of range: 2
QSqlRecord::position: unable to find field url
QSqlRecord::field: index out of range: -1
QSqlRecord::field: index out of range: 3
QSqlRecord::position: unable to find field help_category_id
QSqlRecord::field: index out of range: -1
QSqlRecord::field: index out of range: 0
QSqlRecord::position: unable to find field name
QSqlRecord::field: index out of range: -1
QSqlRecord::field: index out of range: 1
QSqlRecord::position: unable to find field parent_category_id
QSqlRecord::field: index out of range: -1
QSqlRecord::field: index out of range: 2
QSqlRecord::position: unable to find field url
QSqlRecord::field: index out of range: -1
QSqlRecord::field: index out of range: 3
QSqlRecord::position: unable to find field help_category_id
QSqlRecord::field: index out of range: -1
QSqlDatabase warning: QMYSQL3 driver not loaded
QSqlDatabase: available drivers:
Failed to open mysql database: Driver not loaded
Driver not loaded
[root@localhost book]#


i dont know what is wrong here.
pleeese check the code. i think it is not able to access the database. but as i can see all the fields of mysql when i preview the form, so i think there is no problem with the driver.

please do something. one problem gone, another came. i m frustrated now!!:confused:

this really sucks

[wysota]

First thing - please embed the source code into code tags. I have to correct that every time you post any source code, I think it's high time you started using the forum properly.

Second thing - why are you running the application as root?

Third thing - you have to create the connection before creating the data table.

Fourth thing - the driver is still not loaded. Why don't you run the examples as I asked you to?

[shamik]

yes brother

you are right

as i was compiling one of the examples i noticed that the library it was using was /usr/lib/qt-3.1

when i typed 'set' command from the shell the QTDIR path was not set to /usr/local/qt
where i have installed my new qt 3.3.0.

so i had to type the following on the shell
export QTDIR=/usr/local/qt
export PATH=/usr/local/qt:$PATH

and then when i typed the set command again the qtdir path was properly set.

but now whenever i try to compile and form the exe using 'make' command after doing qmake, everytime it gives the following error:
/usr/bin/ld : cannot find -lqt
collect 2 : ld returned 1 exit status
make : *** [sample]E\ Error 1

this error is same for all the programs(projects). so i think i have to set some other paths also.

whats that??

[wysota]

The projects are looking for singlethreaded Qt library (libqt) instead of multithreaded one (libqt-mt). You either have to correct the project files to include CONFIG+=thread (better option) or make a softlink from libqt-mt.so to libqt.so (worse option).

[shamik]

i have soved the previous problem myself. i dont know wheather what i did is right or not.
this is what i did .
i modified the ld.so.conf and properly set the qtdir path.
then i ran 'ldconf' command from shell. then qtdir path was set properly. then i recompiled the driver and that error of 'cannot find -lqt' has gone and the programs are now compiling and exe is also formed.
but the error is the same as i have posted earlier. it comes with two simultneous exclamations saying: "An error occured while accessing the database"
and then followed by that series of QSqlRecord.... (just see the previous to previous post)

you were talking of running the examples for qt3 in some of ur posts. what is that.

also one more thing i noticed.
everytime i restart my pc and type 'set' on the shell the qtdir path which i had set recently i.e. to /usr/local/qt again becomes the previous one which is /usr/lib/qt-3.1
and every time i have to export both QTDIR and PATH. is there any way that i dont have to it everytime i restart.

one more thing.
my-sql devel package has installed( i think) the files i.e. mysqlclient.so and all similar ones in folder /usr/lib/mysql

now notice this :
when i compile the driver with the qmake command as follows :
qmake -o Makefile "INCLUDEPATH+=/usr/local/mysql/include" "LIBS+=-L /usr/lib/mysql -lmysqlclient" mysql.pro

i.e. i give the library path of /usr/lib/mysql
the driver is formed. ok. but qt as usual crashed as our previous problem and all the programs gives relocation error as previously.
when i run ldd on that qsqlmysql.so (driver) then one of the listed file is libmysqlclient.so.10 in /usr/lib/mysql
fine.
but when i compile the driver with qmake command as follows :
qmake -o Makefile "INCLUDEPATH+=/usr/local/mysql/include" "LIBS+=-L /usr/local/mysql/lib -lmysqlclient" mysql.pro
i.e library path is now /usr/local/mysql/lib
the driver is formed. ok. the qt doesnt crash. ok. the connection is also formed. ok. and whenever i preview the form the database contents are also reflected in the datatable.
only that the programs are not running as the present case.
but when i run ldd on this particular 'libqsqlmysql.so' then none of the mysqlclient files are shown. i think it doesnt have any dependencies on mysqlclient libraries. thats the reason it might be having problems accessing database.

this is not as complicated as it seems coz just to give u whole explanation in detail i am writing so long.

my question is :
1). i have to set qtdir path everytime i restart. how to avoid it?
2). as u were telling, how to run examples as qt3? the older version on my system is qt-3.1 and the new is qt-3.3.0.
3). if the preview form can show the database contents then why is the error coming of accessing the database when i run the exe?
4). in ur previous post u were telling about single and multi thread. how to set those better and worse options?

this post is too long but it will give you the entire picture of the problem!!