如果你试图在PyQt5/6或PySide2/PySide6中使用Postgres，你可能遇到了一个加载驱动的问题。 Qt（正确地）列出了驱动在Qt中是可用的，但当试图加载它时，加载将失败。这是因为Qt库依赖于Postgres自己的库，而这个库在加载路径中必须是可用的。
下面的脚本可以让你测试Postgres库的加载是否正确：
- PyQt5
- PyQt6
- PySide2
- PySide6
from PyQt5.QtSql import QSqlDatabase
from PyQt5.QtWidgets import QApplication
app = QApplication([])
db = QSqlDatabase("QPSQL")
print("Available drivers", db.drivers())
if not db.open():
print("Unable to connect.")
print('Last error', db.lastError().text())
else:
print("Connection to the database successful")
from PyQt6.QtSql import QSqlDatabase
from PyQt6.QtWidgets import QApplication
app = QApplication([])
db = QSqlDatabase("QPSQL")
print("Available drivers", db.drivers())
if not db.open():
print("Unable to connect.")
print('Last error', db.lastError().text())
else:
print("Connection to the database successful")
from PySide2.QtSql import QSqlDatabase
from PySide2.QtWidgets import QApplication
app = QApplication([])
db = QSqlDatabase("QPSQL")
print("Available drivers", db.drivers())
if not db.open():
print("Unable to connect.")
print('Last error', db.lastError().text())
else:
print("Connection to the database successful")
from PySide6.QtSql import QSqlDatabase
from PySide6.QtWidgets import QApplication
app = QApplication([])
db = QSqlDatabase("QPSQL")
print("Available drivers", db.drivers())
if not db.open():
print("Unable to connect.")
print('Last error', db.lastError().text())
else:
print("Connection to the database successful")
在一个新的命令提示符下执行上述脚本将得到如下输出（如果Postgres无法访问）。
命令
>python test.py
QSqlDatabase: QPSQL driver not loaded
QSqlDatabase: available drivers: QSQLITE QODBC QODBC3 QPSQL QPSQL7
Available drivers ['QSQLITE', 'QODBC', 'QODBC3', 'QPSQL', 'QPSQL7']
Unable to connect.
Last error Driver not loaded Driver not loaded
可用的驱动 "列表显示了在你的PyQt5（或PyQt6，或PySide2，或PySide6）安装中可用的Qt驱动。例如，在我的安装中，驱动文件在下面。site-packages\PyQt5\Qt5\plugins\sqldrivers
命令
C:\Users\Martin\AppData\Local\Programs\Python\Python37\Lib\site-packages\PyQt5\Qt5\plugins\sqldrivers> dir
Volume in drive C has no label.
Volume Serial Number is 0A6A-65ED
Directory of C:\Users\Martin\AppData\Local\Programs\Python\Python37\Lib\site-packages\PyQt5\Qt5\plugins\sqldrivers
02/12/2021 14:35 <DIR> .
02/12/2021 14:35 <DIR> ..
02/12/2021 14:35 1,412,080 qsqlite.dll
02/12/2021 14:35 98,288 qsqlodbc.dll
02/12/2021 14:35 79,856 qsqlpsql.dll
3 File(s) 1,590,224 bytes
2 Dir(s) 174,429,970,432 bytes free
由于Qt Postgres驱动找不到Postgres库，所以出现了Driver not loaded的错误。Qt Postgres驱动是对这些库的一个封装，而不是对Postgres本身的一个完整实现。
为了使其正常工作，你需要确保所需的Postgres库文件在你的路径中可用。你可以通过将你的Postgres安装bin 文件夹添加到你的路径中来做到这一点。例如，在我的电脑上，Postgres被安装在C:\Program Files\PostgreSQL\14\ （我使用的是14版）。我们需要把Postgres的bin 文件夹添加到PATH ，因为这里包含了Qt需要的libpq.dll （Postgres Access Library）。
命令
SET PATH=%PATH%;C:\Program Files\PostgreSQL\14\bin
有了这些，再次运行脚本会显示该驱动已经成功加载。连接仍然没有工作，因为它需要设置用户名和密码。但如果你走到这一步，你就知道驱动已经正常工作了。
命令
U:\home\martin\www\pythonguis\content\faq\qt-postgres-driver>python test.py
Available drivers ['QSQLITE', 'QODBC', 'QODBC3', 'QPSQL', 'QPSQL7']
Unable to connect.
Last error connection to server at "localhost" (::1), port 5432 failed: fe_sendauth: no password supplied
QPSQL: Unable to connect
我们可以修改测试脚本，加入你的用户名和密码来完成连接：
- PyQt5
- PyQt6
- PySide2
- PySide6
from PyQt5.QtSql import QSqlDatabase
from PyQt5.QtWidgets import QApplication
app = QApplication([])
db = QSqlDatabase("QPSQL")
db.setUserName("postgres") # postgres is the default root username
db.setPassword("") # add your password here
print("Available drivers", db.drivers())
if not db.open():
print("Unable to connect.")
print('Last error', db.lastError().text())
else:
print("Connection to the database successful")
from PyQt6.QtSql import QSqlDatabase
from PyQt6.QtWidgets import QApplication
app = QApplication([])
db = QSqlDatabase("QPSQL")
db.setUserName("postgres") # postgres is the default root username
db.setPassword("") # add your password here
print("Available drivers", db.drivers())
if not db.open():
print("Unable to connect.")
print('Last error', db.lastError().text())
else:
print("Connection to the database successful")
from PySide2.QtSql import QSqlDatabase
from PySide2.QtWidgets import QApplication
app = QApplication([])
db = QSqlDatabase("QPSQL")
db.setUserName("postgres") # postgres is the default root username
db.setPassword("") # add your password here
print("Available drivers", db.drivers())
if not db.open():
print("Unable to connect.")
print('Last error', db.lastError().text())
else:
print("Connection to the database successful")
from PySide6.QtSql import QSqlDatabase
from PySide6.QtWidgets import QApplication
app = QApplication([])
db = QSqlDatabase("QPSQL")
db.setUserName("postgres") # postgres is the default root username
db.setPassword("") # add your password here
print("Available drivers", db.drivers())
if not db.open():
print("Unable to connect.")
print('Last error', db.lastError().text())
else:
print("Connection to the database successful")
...然后连接将如期完成。
命令
>python test-userpass.py
Available drivers ['QSQLITE', 'QODBC', 'QODBC3', 'QPSQL', 'QPSQL7']
Connection to the database successful
