Qt and MySQL Database Connection

[shamik]

hiii,

Please help me connect Qt and MySQL in Linux(RH9). I am using Qt 3.3.0 and MySQL 5.0.0 alpha.

I am not able to do database connection in Qt with MySQL.

When I go to "project->database connections" the only driver that is listed is "QMYSQL3" and after providing the information in all the fields when i click "connect" then the whole window disappears and I have to start Qt again.

I have already installed all the drivers and compiled as is given in the manual.
but still cant connect.

Please help me build this database connection.

Thanks and Regards.
shamik

[wysota]

Qt3 doesn't support MySQL 5.0. About the crash - run QtDesigner under a debugger and see why it crashes. You might be missing some symbols if you don't have a proper mysql client library.

[shamik]

qt3 supports mysql5 and it has been done before by somebody and also has been confirmed by the trolltech support team.

i have compiled the drivers using following qmake command :

qmake -0 Makefile "INCLUDEPATH+=/usr/local/mysql/include" "LIBS+=-L/usr/local/mysql/lib" mysql.pro

make.

it compiled fine.

the driver QMYSQL3 is shown in the driver list in project->database connection.

i have written a small code to setup the database connection.

it also compiles well without error and exe is formed.

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

[root@RedhatLinux database setup]# ./dbsetup
./dbsetup: relocation error: /usr/local/qt/plugins/sqldrivers/libqsqlmysql.so: undefined symbol: mysql_server_init
[root@RedhatLinux database setup]#

i dont know what to do know. i think all the libraries are included and all the paths are set correctly. the file libqsqlmysql.so also exists in the given folder.

please tell me whatz wrong here.

shamik

[wysota]

qt3 supports mysql5 and it has been done before by somebody and also has been confirmed by the trolltech support team.

Yes, but probably not out of the box.

i have compiled the drivers using following qmake command :

qmake -0 Makefile "INCLUDEPATH+=/usr/local/mysql/include" "LIBS+=-L/usr/local/mysql/lib" mysql.pro

Do you have /usr/local/mysql/lib in your linker path?

the driver QMYSQL3 is shown in the driver list in project->database connection.

Are you sure it is the same driver you compiled? Did you install the driver? Compiling it is not enough, it should be put in an appropriate place for Qt to find it.

i have written a small code to setup the database connection.

Can you present the code here?

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

[root@RedhatLinux database setup]# ./dbsetup
./dbsetup: relocation error: /usr/local/qt/plugins/sqldrivers/libqsqlmysql.so: undefined symbol: mysql_server_init

Make sure the plugin tries to link against the proper mysqlclient library. You can do that using ldd.

[shamik]

hii,

thanks for the detailed information.

the code is here :

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

int main(int argc, char **argv)
{
Qapplication a(argc,argv);
QsqlDatabase *defaultDB=QsqlDatabase::addDatabase(“QMYSQL 3”);
defaultDB->setDatabaseName(“manager”);
defaultDB->setPassword(“ “);
defaultDB->setHostName(“localhost”);

if(defaultDB->open())
{
qWarning(“Database connection successful”);
}

else
{
qWarning(“Database connection failed”);
}

return a.exec();

}

and yes, please tell what do u mean by
"Yes, but probably not out of the box."
"Do you have /usr/local/mysql/lib in your linker path?"

i have compiled the same driver.
and yes i have inquired about the plugin,

i think it requires, mysqlclient.so.15, as somebody else suggested me, but i am not sure. As against this i have got mysqlclient.so.10 which gets installed after i install mysql-devel package.

if this is the case then can you please tell me where can i get this *.*15 file from. how can i download it or the entire package which contains this file.

regards
shamik

[wysota]

and yes, please tell what do u mean by
"Yes, but probably not out of the box."

I mean that binary distributed qmysql3 plugins won't use the mysqlclient library from MySQL5. You have to recompile the driver from sources.

"Do you have /usr/local/mysql/lib in your linker path?"

I mean does your linker know to look for libraries in /usr/local/mysql/lib?

i think it requires, mysqlclient.so.15, as somebody else suggested me, but i am not sure.

That's very bad, as you ought to be sure. Use ldd on the driver to find out what it needs and what it finds.

As against this i have got mysqlclient.so.10 which gets installed after i install mysql-devel package.

And probably it gets linked with the driver instead of the version from MySQL5 causing relocation errors.

if this is the case then can you please tell me where can i get this *.*15 file from. how can i download it or the entire package which contains this file.

Install MySQL5 on your system. And make sure the dynamic linker can find it.

BTW. Does this thread have anything to do with Designer? Moving to Qt Programming. Or maybe it should end up in "Installation"?

[shamik]

ya thanks

i know it has got nothing to do with designer, ill surely move it to installation, but before that tell me how to move this thread.

and yes i know dont know which is the exact driver, wheather it is mysqlclient.so.10 or ..15. the connection doesnt work with 10. but cant say wheather definitely it is 15. if you know then please tell me. i cant find any source to know this. also in mysql.com and other sites also i have searched for the same, but i dint even got ..15.

as i told you i have done a new fresh instalation, i am quite sure that the actual driver only gets linked. i have posted the qmake command which i use.
the errors all the remain same after the installation too.

and about installig mysql5, let me inform you that the project is already in use in "indian space research organization" and we are just adding a new feature to it. so my seniors are not convinced about changing any kind of specification in the softwares used to build up the project. thats the tragedy with me that even after such advanced version of qt, kdevelop, mysql and redhat, i have to still work on with the older ones.

can you tel me wheather i m using the correct driver or not. its mysqlclient.so.10. if not then please tell me which is the correct one. from where can i get it.

[wysota]

i know it has got nothing to do with designer, ill surely move it to installation, but before that tell me how to move this thread.

You can't. I can and I already did.

and yes i know dont know which is the exact driver, wheather it is mysqlclient.so.10 or ..15. the connection doesnt work with 10. but cant say wheather definitely it is 15. if you know then please tell me. i cant find any source to know this. also in mysql.com and other sites also i have searched for the same, but i dint even got ..15.

I have already told you -- use ldd.

as i told you i have done a new fresh instalation, i am quite sure that the actual driver only gets linked.

Sure it gets linked, but against what?

i have posted the qmake command which i use.
the errors all the remain same after the installation too.

Because it has nothing to do with Qt, only with linker path.

can you tel me wheather i m using the correct driver or not. its mysqlclient.so.10. if not then please tell me which is the correct one. from where can i get it.

mysqlclient.10 is an old library, MySQL 3.3 I think...

I suggest you read a little about things such as dynamic linking, ldd, ldconfig, LD_LIBRARY_PATH and /etc/ld.so.conf.

[shamik]

hii there

now let me make somethings clear which i have come to know recently

all the installation cds which we use are made by those who have already made the software using these. those guys have now left the company and we have lost contact with them. we only have to add a new feature to the existing one. so compulsorily we have to use these softwares only. and since these have worked in the past it should work now also right?

what happened today is in one of the pcs the when i pressed 'connect' in 'project->database settings' the qt window dint disappear as it used to.
the settings under that are as follows
connection name : default
driver : QMYSQL3
database name : mysql
user : root
password :
host : localhost
port : default

and when press connect the following exclamation had come :

"
Could not connect to database.
Please ensure that the database server is running and that all the connection information is correct.
[QMYSQL3 : Unable to connect.
Cant connect to local MySQL server through socket 'tmp/mysql.sock' (2)]
"
the file mysql.sock is present in /var/lib/mysql dir. and not in /tmp
and now there are now problems in running mysql as we were facing previously. the only thing is that everytime i start mysql i have to run /etc/init.d/mysqld start .

and yes the mysql server is running when i see under server setting->services.

i have also tried to run the code which i have already posted.

when i try to run the exe from the shell it gives following error: (exe's name is driver)

QSqlDatabase Warning : QMySQL3 driver not loaded
QSqlDatabase : available drivers :
Database Connection failed (this is the message from our code)
[2]+stopped ./driver

so this all is new.

now lets go back again.
in my pc as you told to try out ldd
i tried it on libqsqlmysql.so which is in /usr/local/qt/plugins/sqldrivers
it listed the library file of mysql called libmysqlclient.so.10 along with many others.

when i try to run nm on this file which is in /usr/lib/mysql/ it says no symbols found
again on the file libqsqlmysql.so i had tried out nm and it shows that mysql_server_init is undefined.

now i am quite sure that the file ..10 is the correct driver and not ..15 because this has been done before by somebody.

what now!!?!?

shamik

[wysota]

i tried it on libqsqlmysql.so which is in /usr/local/qt/plugins/sqldrivers
it listed the library file of mysql called libmysqlclient.so.10 along with many others.

So it links against MySQL3 and not MySQL5 client library.

when i try to run nm on this file which is in /usr/lib/mysql/ it says no symbols found

That's because the library is stripped, don't worry, that's perfectly normal.

again on the file libqsqlmysql.so i had tried out nm and it shows that mysql_server_init is undefined.

That's normal too, because it will be defined when dynamic loader links the driver against mysql library.

now i am quite sure that the file ..10 is the correct driver and not ..15 because this has been done before by somebody.

So you need MySQL3 or MySQL5? Do you have libmysqlclient.so.10? (locate libmysqlclient.so should help find it)

what now!!?!?

Does ldd report any missing paths? (try ldd libqsqlmysql.so|grep "not found" or something simmilar)

From the message you provided I can see that the driver plugin can't be loaded. It is either not found at all (where is the file located?) or it can't find one of its dependencies (ldd should verify that).

[shamik]

So it links against MySQL3 and not MySQL5 client library.


no, but i told u that it should work against mysql5 also as it has been done before.


So you need MySQL3 or MySQL5? Do you have libmysqlclient.so.10? (locate libmysqlclient.so should help find it)

ya i have libmysqlclient.so.10 and it is /usr/lib/mysql directory.

Does ldd report any missing paths? (try ldd libqsqlmysql.so|grep "not found" or something simmilar)

this is the result of ldd:

[root@localhost sqldrivers]# ldd libqsqlmysql.so
libmysqlclient.so.10 => /usr/lib/mysql/libmysqlclient.so.10 (0x40023000)
libqt.so.3 => /usr/local/qt/lib/libqt.so.3 (0x4005a000)
libXrender.so.1 => /usr/X11R6/lib/libXrender.so.1 (0x4081e000)
libXrandr.so.2 => /usr/X11R6/lib/libXrandr.so.2 (0x40826000)
libXcursor.so.1 => /usr/X11R6/lib/libXcursor.so.1 (0x4082b000)
libXft.so.2 => /usr/X11R6/lib/libXft.so.2 (0x40834000)
libfreetype.so.6 => /usr/lib/libfreetype.so.6 (0x40846000)
libfontconfig.so.1 => /usr/lib/libfontconfig.so.1 (0x40897000)
libXext.so.6 => /usr/X11R6/lib/libXext.so.6 (0x408bc000)
libX11.so.6 => /usr/X11R6/lib/libX11.so.6 (0x408ca000)
libSM.so.6 => /usr/X11R6/lib/libSM.so.6 (0x409aa000)
libICE.so.6 => /usr/X11R6/lib/libICE.so.6 (0x409b3000)
libdl.so.2 => /lib/libdl.so.2 (0x409ca000)
libstdc++.so.5 => /usr/lib/libstdc++.so.5 (0x409cd000)
libm.so.6 => /lib/tls/libm.so.6 (0x40a80000)
libgcc_s.so.1 => /lib/libgcc_s.so.1 (0x40aa2000)
libc.so.6 => /lib/tls/libc.so.6 (0x42000000)
libz.so.1 => /usr/lib/libz.so.1 (0x40aab000)
libcrypt.so.1 => /lib/libcrypt.so.1 (0x40ab9000)
libnsl.so.1 => /lib/libnsl.so.1 (0x40ae6000)
libexpat.so.0 => /usr/lib/libexpat.so.0 (0x40afb000)
/lib/ld-linux.so.2 => /lib/ld-linux.so.2 (0x80000000)
[root@localhost sqldrivers]#ldd libqsqlmysql.so | grep "not found"
[root@localhost sqldrivers]#



From the message you provided I can see that the driver plugin can't be loaded. It is either not found at all (where is the file located?) or it can't find one of its dependencies (ldd should verify that).

so as ldd doesnt report anything missing , everything else is fine.
i think i am just little bit far from the end.

[wysota]

Where is libqsqlmysql.so and what paths are mentioned by qtconfig as library paths?

[shamik]

libqsqlmysql.so is in /usr/local/qt/plugins/sqldrivers

there are two paths mentioned under library paths tab when i type ./qtconfig they are

/usr/local/qt/plugins
/usr/local/qt

[wysota]

Seems fine... And what does QSqlDatabase::drivers() return?

One more thing I just thought of... Are you sure you're not trying to access an embedded mysql database using a client only library? mysql_server_init() symbol name suggests trying to use an embedded database, which is available in libmysqld.so not in libmysqlclient.so. Did you compile the qsqlmysql driver yourself? What switches did you pass during compile process?

[shamik]

no i think i am not trying to access an embedded mysql database.

and i have tried alot but i am not able to write a code to print the list of drivers using QSqlDatabase::drivers()

actually i am able to store the list, this function returns but i dont know how to print that list.

i think QMYSQL3 might be the only driver since only this is listed under project->database settings->driver

what say!!

[wysota]

no i think i am not trying to access an embedded mysql database.

You think that or you verified that?

and i have tried alot but i am not able to write a code to print the list of drivers using QSqlDatabase::drivers()
actually i am able to store the list, this function returns but i dont know how to print that list.

QStringList slist = QSqlDatabase::drivers();
for(int i=0;i<slist.size();i++) qDebug("%s", slist[i].ascii());

QStringList slist = QSqlDatabase::drivers();
for(int i=0;i<slist.size();i++) qDebug("%s", slist[i].ascii());

To copy to clipboard, switch view to plain text mode 

i think QMYSQL3 might be the only driver since only this is listed under project->database settings->driver

It's not a matter of thinking, it's a matter of checking different possibilities to find out what the problem is.

What about answers to my other questions?

[shamik]

ok
the code gives the list -- QMYSQL3
and i have to stop the program manually by pressing ctrl-Z

ofcourse i have compiled the driver myself using the qmake which i have submitted.
and m sorry i dont know what are switches.

and can you tell me (going back to our previous prob) why does the qt crashes when i press connect. i dont know how to open and run it under any debugger. i have tried using the debugger present in programming-debugger and failed miserably.

moreover in other pc as the problem i have told you about, it gives the error that it cant connect through socket /tmp/mysql.sock. this file is not present there but exists in /var/lib/mysql/

how to tell qt to change the path into which it is looking. i have added a library path -- /var/lib/mysql in qtconfig. but can see no difference.

[wysota]

using the qmake which i have submitted.

What do you mean by that?

and m sorry i dont know what are switches.

Commandline parameters passed to configure.

and can you tell me (going back to our previous prob) why does the qt crashes when i press connect.

You mean the relocation error? It is because when a plugin is loaded, the dynamic linker has to resolve all the symbols from the plugin and its dependencies. And it fails to do so.

i dont know how to open and run it under any debugger. i have tried using the debugger present in programming-debugger and failed miserably.

If it is a relocation error, then the debugger won't help you. But if you want to check other things, then try this:
$ gdb ./your_application
(gdb) run
(...)
(gdb) bt

This will give you the backtrace -- a list of calls which led to the error.

moreover in other pc as the problem i have told you about, it gives the error that it cant connect through socket /tmp/mysql.sock. this file is not present there but exists in /var/lib/mysql/

You have to instruct MySQL to put it in /tmp or convince the driver (using my.cnf I think) to look for it elsewhere.

how to tell qt to change the path into which it is looking. i have added a library path -- /var/lib/mysql in qtconfig. but can see no difference.

It is MySQL which fails, not Qt.

[shamik]

hiii there

thanks alot for the help
finally i have done the connection (in other pc, though not in mine). the very small thing took a hell lot of time.
thanks alot for that.

what i did is just changed the path in my.cnf to /tmp

but wait a min. in my pc the error is same old one and got to solve it.
about the switches you told , i dont pass anything in that. what i do is simply type:
./configure

and then

make.

then i install the mysql-devel package and then run qmake as under :
1) qmake -o Makefile "INCLUDEPATH+=/usr/local/mysql/include" "LIBS+=-L/usr/lib/mysql" mysql.pro

2) qmake -o Makefile "INCLUDEPATH+=/usr/local/mysql/include" "LIBS+=-L/usr/local/mysql/lib" mysql.pro

3) qmake -o Makefile "INCLUDEPATH+=/usr/local/mysql/include" "LIBS+=-L/usr/local/mysq/lib -lmysqlclient" mysql.pro

i have tried all the three of these, but none works.
i am planning to install qt again in my pc and start from scratch. i usually follow the instructions given in the "install" file in the qt folder.

can u tell me the step by step process of qt installation if anywhere i am going wrong?

and yes one more thing. we already had qt 3.1.1 installed with linux but we have installed qt3.3.0.
now we want to integrate it with kdevelop. when we click the qt icon given in the kdevelop gui the new version i.e. qt3.3.0 opens up. thats fine and as we wanted.

but when we try to add new qt ui file to new project or existing project by going into
file->new->qtdesigner(*.ui), give the file name and then click ok then the older qt3.1.1 gets open. i want that new qt should get opened. do you know anything about this.

if possible then tell me otherwise our previous problem is more important.
and i think we are about to get it done.

thanks again

[wysota]

Install mysql development packages before compiling Qt. Otherwise it won't know that it is to compile the plugin at all or will link it against some other mysql library. Also make sure that mysql installation you performed is seen "by default" by the system. Otherwise you might need to pass some switches to configure (see configure -help for details).