What is the right way to use PostgreSQL with PyQt5

[Nenad Lamza]

I use PostgreSQL 9.6.17 (installed on linux server on LAN) and have 
Win10 (or Win7) clients with installed Python 3.7 or 3.8 and PyQt 
5.13.2, and my PyQt5 app that uses that PostgreSQL server works ok, but 
I really don't know what I'm doing.

I'll describe the problem. If I don't have PostgreSQL installed on Win 
client (I don't need it because I use PostgreSQL on linux server) or 
have installed it but not in path, my app crashes with the error: 
"QSqlDatabase: QPSQL driver not loaded".

So, I need some drivers. And I install PostgreSQL 9.6.x on Win client 
and have it in path and after that everything works ok, but only if I 
had luck and picked the right x in PostgreSQL 9.6.x version.

The alternative is that I don't install PostgreSQL 9.6.x (why would I 
need to install it) on client machine and just copy some dll files at 
the app directory. If I find the right files (drivers), everything works 
ok, but if I don't, the app crashes with the error: "QSqlDatabase: QPSQL 
driver not loaded" or worse, recognize the PostgreSQL database on 
server, works ok some time, but after the first, second or third query 
it crashes.

Some driver combinations I copy to my app directory that work with PyQt 
5.13.2:

1.
Timestamp                      Size             File
25/02/2016  07:19         1,015,973 libiconv-2.dll
07/01/2016  09:02         1,550,023 libintl-8.dll
10/07/2019  20:20           145,408 libpq.dll

2.
Timestamp                      Size             File
21/06/2019  14:43         1,218,048 libeay32.dll
25/02/2016  07:19         1,015,973 libiconv-2.dll
07/01/2016  09:02         1,550,023 libintl-8.dll
10/07/2019  20:20           145,408 libpq.dll
21/06/2019  14:43           276,992 ssleay32.dll

If I install PyQt 5.14 or 5.15 (instead of PyQt 5.13.2), the app 
crashes, and I am afraid to upgrade PyQt5.

So, my question is:
How do I know which drivers I should copy to my app directory with 
various version of PyQt5, that's the mistery to me. And also if copying 
the drivers to my app directory is the right way at all?

There's a fine answer here:

https://stackoverflow.com/questions/20884010/qt5-failed-to-load-psql-driver-in-windows

"It's quite likely to be failing because there's a dependency of 
|qsqlpsql.dll| missing - either |libpq.dll|, or one of the libraries 
that |libpq| build requires." ... "You should use the /same/ libpq your 
Qt's |qsqlpgsql.dll| was compiled against if possible."

If that's true, how should I know with what libpq library qsqlpgsql.dll 
was compiled in. I suppose PyQt 5.13.2's qsqlpgsql.dll is compiled with 
different version than PyQt 5.14.x's qsqlpgsql.dll or even 5.15.x's 
qsqlpgsql.dll.

Also, this link has some clues:
https://stackoverflow.com/questions/26507353/qpsql-driver-not-loaded-qt

And generally, what's the best way to work with PostgreSQL in PyQt5. It 
obviously doesn't work out of the box if PostgreSQL is not installed on 
client machine, and even if the wrong version is installed.

Nenad

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