Postgresql driver is not found

[alxdef]

Re: POSTGRES QPSQL not loading

Hello!
I have old problem with new soft. Got a message "Cannot load library C:\Qt\5.15.2\mingw81_64\plugins\sqldrivers\qsqlpsql.dll"
on Win 10 Pro x64 and Postgresql 13 x64. The path is valid.
I've smoked all web sources about this problem, used all advices but nothing changed. Is there any solution?

[JonB]

@alxdef
Start with checking with a suitable Dependency Walker. Otherwise what didn't work in the proposals in the thread you reference?

[alxdef]

@JonB

Here DW output:

But DW fault with this:

1. I tried to add paths to Postgres "bin" and "lib" folders - no way.
2. Copy DLLs to different folders: "build", "plugins\build" and other variations - no luck.
3. I didn't build database libraries myself.

[SGaist]

Hi and welcome to devnet,

On Qt Creator, add the QT_DEBUG_PLUGINS environment variable set to 1 in the Run part of the project panel. You'll have more information about what is going wrong.

[alxdef]

@SGaist
Hi there!
I've already done this. The message I got is directly from application output.

[SGaist]

In the list of plugins information dumped in your application, you should have why the plugin failed to load. You did not show that in what you posted.

[alxdef]

@SGaist
Here the supplement message to my first one: "QLibraryPrivate::loadPlugin failed on "C:/Qt/5.15.2/mingw81_64/plugins/sqldrivers/qsqlpsql.dll""

[SGaist]

Can you should the complete output of your application ?

[alxdef]

@SGaist
Here the part of application output about DLL load failure:

Got keys from plugin meta data ("QPSQL7", "QPSQL")
QFactoryLoader :: QFactoryLoader () checking directory path "…/ build-MCS-Desktop_Qt_5_15_2_MinGW_64_bit-Debug / Shell / debug / sqldrivers" …
Cannot load library C: \ Qt \ 5.15.2 \ mingw81_64 \ plugins \ sqldrivers \ qsqlpsql.dll: The specified module could not be found.
QLibraryPrivate :: loadPlugin failed on "C:/Qt/5.15.2/mingw81_64/plugins/sqldrivers/qsqlpsql.dll": "Cannot load library C: \\ Qt \\ 5.15.2 \\ mingw81_64 \\ plugins \\ sqldrivers \\ qsqlpsql.dll: The specified module could not be found. "
QSqlDatabase: QPSQL driver not loaded
QSqlDatabase: available drivers: QSQLITE QODBC QODBC3 QPSQL QPSQL7

Tell me what additional information is needed?

[SGaist]

Just remembered something, check that you have also copied the dependencies of the PostgreSQL .dll.

[alxdef]

@SGaist
Am I on the right way? Which of them should be added in project executable folder?

[SGaist]

The OpenSSL related

[alxdef]

@SGaist said in Postgresql driver is not found:

The OpenSSL related

Not works.

[SGaist]

Then run Dependency Walker on these.
The next likely candidate is the VC runtime dll.

[alxdef]

@SGaist

I think that library is not in business.

[SGaist]

I meant that you should run Dependency Walker on the OpenSSL dlls and that it would have likely been the VC runtime missing.

[alxdef]

@SGaist

It looks like infinite loop…

[SGaist]

Did you copy the VC runtime in the same folder as the OpenSSL library ?

[Christian Ehrlicher]

@alxdef Your first screenshot tells you that libstdc++-6.dll is missing.

[SGaist]

@Christian-Ehrlicher said in Postgresql driver is not found:

@alxdef Your first screenshot tells you that libstdc++-6.dll is missing.

Arf ! I missed that one. Good catch :-)

[alxdef]

@Christian-Ehrlicher

These libs are present in my app executable folder:

sqldrivers\qsqlpsql.dll
platforms\qwindows.dll
vcruntime140.dll
Qt5Sql.dll
Qt5Core.dll
msvcrt.dll
libstdc++-6.dll
libssl-1_1-x64.dll
libpq.dll
libintl-8.dll
libcrypto-1_1-x64.dll

[alxdef]

So there are no ideas…

[Bonnie]

Did you get libpq from the official site? I've just had a try.
I think it is probably due to the file you were all ignoring: libintl-8.dll --> it depends on libiconv-2.dll, which you didn't copy.
When you use Dependency Walker on libpq.dll, check all the yellow icons, not only in the upper part tree, but also in the lower part list (those are all the dlls recursively)...
But there may also be some many "false alarms", especially those dlls needed by system dlls / vc runtimes (e.g.: api-ms-...), you'll need to distinguish them by yourself.
I mainly check those start with "lib" (MinGW style) and "q" (Qt libs).
Or you can manually expand all the tree items recursively, just skip when it is a system / vc runtime.

[alxdef]

@Bonnie
Thanks for advice. Now application debug output looks like this:

Got keys from plugin meta data ("QPSQL7", "QPSQL")
loaded library "…/debug/sqldrivers/qsqlpsql.dll"
QFactoryLoader::QFactoryLoader() checking directory path "…/debug/accessible" ...
QFactoryLoader::QFactoryLoader() checking directory path "…/debug/accessiblebridge" ...
QLibraryPrivate::unload succeeded on "…/debug/sqldrivers/qsqlpsql.dll" 
QLibraryPrivate::unload succeeded on "…/debug/platforms/qwindows.dll" 
21:31:17: *.exe exited with code 0

But I still catch "Driver not loaded" using this code:

if (!this->app_conn.isValid())
{
  //…
}

if (!this->app_conn.open())
{
  //…
}

[SGaist]

Can you show the code your are actually using to setup the database ?

The output you show does not present any error quite the contrary.

[alxdef]

@SGaist

this->app_conn = QSqlDatabase();

  this->app_conn.addDatabase(this->db_type);
  this->app_conn.setDatabaseName(this->db_name);
  this->app_conn.setHostName(this->db_host);
  this->app_conn.setPort(this->db_port);
  this->app_conn.setUserName(this->user_name);
  this->app_conn.setPassword(this->user_password);

this->db_type is "QPSQL".

[SGaist]

You are using QSqlDatabase in the wrong manner.

addDatabase is a static member, you are manipulating an invalid object.

As the QSqlDatabase warns about: do not store local variables of that type. The class already provides everything needed to handle the objects you create from it.

[alxdef]

@SGaist said in Postgresql driver is not found:

QSqlDatabase

Many thanks! Connected Ok.

[alxdef]

So is it necessary to grab all "Debug" DLLs and place them to "Release"? How to avoid this crutch?

[SGaist]

What debug dll ?

[alxdef]

@SGaist

\sqldrivers\qsqlpsql.dll
\platforms\qwindows.dll
\vcruntime140.dll
\Qt5Sql.dll
\Qt5Core.dll
\msvcrt.dll
\libstdc++-6.dll
\libssl-1_1-x64.dll
\libpq.dll
\libintl-8.dll
\libiconv-2.dll
\libcrypto-1_1-x64.dll

[SGaist]

Ah, you meant the content of the Debug folder.

One thing you can do is go in the Run part of the Project panel and modify the PATH environment variable to include the path to these dlls.

[alxdef]

@SGaist
I've made additional folder inside my project and move all DLLs into it. After that add path to this folder in PATH variable. It works but this method is crutch anyway…

[SGaist]

On Windows there's two way to find .dlls:

• they are in the same folder
• they are in a folder in your PATH environment variable

Qt Creator does the change for Qt for you based on which kit you are using. Since you use external dependencies, it's up to you to provide a mean to find your dependencies dlls. And no, modifying your system's PATH environment is not the correct way.

[Bonnie]

@alxdef
Why?
On windows the most usual way is just putting the dependency dlls with the exe, famous software products also do like that.