How to access Postgresql using Qt in Windows

Question

I am developing an application using QtRuby and PostgreSQL. I successfully developed and running successfully in Linux. Now i want to run the same application in windows. But I am failing to connect to database(postgresql). I am getting the following errors:

 QSqlDatabase: QPSQL driver not loaded
 QSqlDatabase: available drivers: QSQLITE QODBC3 QODBC

Answer 1

As the error message says, the QPSQL driver is not available for Qt to talk to Postgres with. Probably the plugin has not been compiled yet.

As this how-to indicates, you need to install the PostgreSQL developer libraries, and then manually build the Qt driver plugin. See the how-to for the exact commands.

Answer 2

Postgresql using QT in Windows:

1) check installation directory, in my pc:

PostgreSQL (32 bit)    C:\PSQL32\bin
Qt (32 bit)            C:\QT\4.8.0\bin
MingW32                C:\QT\qtcreator-2.4.0\mingw\bin      

2) add these 3 directory to system PATH

3) Download 'mingw-utils' and install in C:\\Qt\\4.8.0\\bin (need utility REIMP.exe)

4) Convert libpq.lib in useful format for mingw32:

CD C:\\PSQL32\\lib

REIMP -d libpq.lib

Open libpq.def and delete ALL "_" at the beginning of definitions

dlltool --input-def libpq.def --output-lib libpq.a --dllname libpq.dll

5) Compile:

CD C:\\Qt\\4.8.0\\src\\plugins\\sqldrivers\\psql

qmake -o Makefile "INCLUDEPATH+=C:\\PSQL32\\include" "LIBS+=C:\\PSQL32\\lib\\libpq.a" psql.pro

mingw32-make debug

mingw32-make release

10) copy dll:

libqsqlpsqld4.a   qsqlpsqld4.dll    (debug)  

libqsqlpsql4.a   qsqlpsql4.dll      (release)

in the directory:

C:\Qt\4.8.0\plugins\sqldrivers

---

there is a multiple definitions of struct timespec

in file of PostgreSQL (C:\\PSQL32\\include\\pthread.h) 文件中（C：\\ PSQL32 \\ include \\ pthread.h）

replace:

#ifndef HAVE_STRUCT_TIMESPEC

with:

#if ((!defined(_TIMESPEC_DEFINED)) && (!defined(HAVE_STRUCT_TIMESPEC)))

---

Done :-)

Answer 3

Great! It's done! However there are some tips to pay attention: 1. Mingw-utils, 0.4-1 will not work on Windows 7, we must use 0.3. 2. There is a psql.json file in the directory of PSQL driver, please don't delete it.

Answer 4

1. Compile the QPSQL plugin as instructed here: http://ldc.usb.ve/docs/qt/sql-driver.html#qpsql-for-postgresql-version-7-3-and-above
2. Add the PostgreSQL bin path to your PATH environment variable