Application does not connect to database when deployed on another computer - mysql

Question

I built a qt application that connects and queries a database using mysql . it works perfectly fine on my development computer (the computer with Qt Creator on it). but when I deploy it using windeployqt.exe and run it on another computer it doesn't connect to the database for some odd reason.
Note that I do have a working database (mysql as well) on the other computer (the one that fails to connect to the database)
I'm not sure what to do, I tried using addLibraryPaths but it didn't work (I'm not even sure if I did it correctly).
I'm using :
mysql server 5.5.36
workbench 6.0
Qt Creator 5.4.0
I also tried looking into statically building my application but I failed to understand the procedures in doing so.
I would greatly appreciate it if any of you Qt gods could help with this.

Answer 1

i finally found the problem and solved it.
problem: for some reason the target computer wasnt recognizing or reading libmysql.dll in C:\Windows ,and thanks to #Marco i used db.LastError and got my application to display the error , it was "Driver not Loaded Driver not Loaded" which meant that there was something wrong with libmysql.dll (note i copied this dll from MySql folder installed on the target machine )
Solution : i had to copy libmysql.dll from my development machine and place it in C:\Windows on the target machine (i noticed that libmysql.dll on my target machine was smaller in size than the one i used on my development machine)
for some reason the program only operates when the libmysql.dll from the development machine is present in C:\Windows in the target machine
this solution should fix any "Driver not loaded" or "QMySQL driver not loaded "(etc) errors . thanks everyone for trying to help , thanks again #Macro

Answer 2

I assume you built your application in release mode instead of debug mode.
If you have libmysql.dll and qsqlmysql.dll alongside your executable. Create a directory/folder and name it sqldrivers. Place qsqlmysql.dll in the directory you created and deploy it alongside your executable.
PS: I didn't see nnb's comment earlier. I think he's saying the same thing as my answer

Answer 3

From the comment we have cleared that there is a problem loading the driver, I am confident that you have the put qsqlmysql.dll in the correct place, as you have used the deploying utility, so I suspect that the problem is qsqlmysql.dll needs another dll that cannot be found in the system path.
I suggest that you run this tool:
http://www.dependencywalker.com/ on the qsqlmysql.dll
That will help you finding out what is missing, when you find that out, you will probably have to modify the system path or to install a dll that is missing.

Answer 4

I know this thread is old, but I've been having the same issue, and the solution was very easy (once you know).
The problem is that when you execute your application inside Qt, it will find the needed dll to load the drivers (libmysql.dll) if you located it in the correct Qt folder (Qt/path_to_compiler/bin), in my case: C:\Qt\5.9.1\msvc2017_64\bin. But when you try to execute the deployed executable, it is not able to find it. You will notice that the problem is solved if you paste the dll in C:\Windows, as #Nelioussness said. But that's not the solution, as it won't work in a different computer.
Just go to MySQL installation folder and look for the file libmysql.dll if you didn't do it before. In my case, it was located in C:\Program Files\MySQL\MySQL Server 5.7\lib. Once you find it, copy it to your release folder, exactly at the same level as the executable. It didn't work for me when I put it inside 'sqldriver' folder and everything was solved by just putting it outside, next to the .exe
Hope this helps :)