MongoDB integration with Qt

enne9

Hello,
in my current project, I'm trying to move from MySQL to MongoDB.
Any idea about where to start? I didn't find anything really clear and recent, maybe someone can point me in the right direction.

In particular, I'm searching for some basic examples of usage and especially how to deal with driver installation.
Thanks

Christian Ehrlicher

Qt has no driver for MongoDB, you have to use the MongoDB api directly or write a Qt driver for it, see for example here: https://forum.qt.io/topic/37645/how-to-connect-mongodb-with-qt/4 (the search function is your friend)

enne9

I already saw it but all github links are broken.

Christian Ehrlicher

As I already said you've three possibilities

don't use MongoDB
write a proper Qt plugin
use the MongoDB api directly.

SGaist

Hi,

Did you check the official MongoDB C API ?

enne9

I did as you suggested to me and I'm including the mongocxx library.
Unfortunatelly I get a
usr/local/include/bsoncxx/v_noabi/bsoncxx/types.hp:39: Parse error at "{"
and I don't know what to do, since a collage of mine working on the same project is not getting this problem (using the exact same code).

The error is in correspondence of

enum class type : std::uint8_t {
#define BSONCXX_ENUM(name, val) k_##name = val,
#include <bsoncxx/enums/type.hpp>
#undef BSONCXX_ENUM
};

If I remove type : std::uint8_t it then complains about other errors...
Any suggestions?

SGaist

Hi,

Can you show the code that you are using that triggers that error ?

enne9

Sorry, but it is confidential and I'm not sure I can share it.
Using #ifndef Q_MOC_RUN as suggested here https://bugreports.qt.io/browse/QTBUG-80578 makes the compilation error disappears but the program then crashes immediately at runtime.

SGaist

In that kind of case, you can also provide a minimal example that shows the issue.

And what does the stack trace of the crash say ?

enne9

home/../mongo/bsoncxx/v_noabi/bsoncxx/types.hp:39: Parse error at "{"
make[1]: *** [Makefile:1117: moc_server.cpp] Error 1

This is what I get in the compilation output, if it is useful

SGaist

Well, without the code, it doesn't help much.

enne9

A minimal piece of code to reproduce the error is already available here https://bugreports.qt.io/browse/QTBUG-80578, but it seems to be a bug. Unfortunately, I didn't find any workaround and I'm unable to continue with the project.

SGaist

You wrote that the compilation was successful so that part is fine, isn't it ?

As for the run time crash, what is the stack trace ?

enne9

SGaist

Do you have the same issue if you write a minimal test application using only bsoncxx ?

enne9

In the end, it was a problem of compatibility between mongocxx and my Qt version. Installing a previous release fixed the issue.

Ahmed000001

@enne9 said in MongoDB integration with Qt:

n mongocxx and my Qt version. I

so, what was the compatible versions?

plaristote

I confirm that I have the very same issue with Qt 5.15.2 and mongo-cxx-driver 3.5.0 (had to add Q_MOC_RUN defines, and then the same crash when building mongocxx::client).

If the author of the thread show up again, which combination of version did you use that worked ? Did you perhaps use the legacy mongo-cxx-driver ? Considering how different the two are, it might work... but the new generation of mongo-cxx-driver is already pretty damn mature, and the legacy one has reached end of life, so it's not really a viable solution on the long term.

EDIT: Alright, the original author wording lacked precision: this has nothing to do with the combined use of Qt and mongo-cxx-driver.
The problem is due to linking to a certain version of the mongo-cxx library, while using the includes for another version.

Turns out I had already installed mongocxx elsewhere, and the CMake package files for mongo-cxx-driver seem to have some issue finding the include files on its own, so that issue might happen if you're not careful enough and mess up the include part.

qxorm

Hello,

If you want an easier integration with Qt and MongoDB, you can try QxOrm library.
The documentation can be found here.
And here is a project example on GitHub.

Please note that the latest commit on GitHub for QxOrm library supports Qt6.