PyQt5:将扩展加载到 sqlite 中

Question

我开始使用 PyQt5 及其带有 sqlite 的 Sql 类。我想将扩展加载到 sqlite 中。为此，必须在运行时为 sqlite 启用扩展加载。在 python 模块 sqlite3 中，这是通过 enable_load_extension 实现的。

C++sqlite句柄可以像这样获得(取自 https://doc.qt.io/qt-5/qsqldriver.html#handle(：

QSqlDatabase db = QSqlDatabase::database();
QVariant v = db.driver()->handle();
if (v.isValid() && (qstrcmp(v.typeName(), "sqlite3*") == 0)) {
// v.data() returns a pointer to the handle
sqlite3 *handle = *static_cast<sqlite3 **>(v.data());
if (handle) {
// ...
}
}

蟒蛇等价物是

from PyQt5.QtSql import QSqlDatabase
db = QSqlDatabase.addDatabase('QSQLITE')
db.driver().handle()
-> TypeError: unable to convert a C++ 'sqlite3*' instance to a Python object

作为旁注，在 Pyside2 中，句柄方法没有公开。

这似乎是错误的方法。有什么方法可以通过 PyQt5 加载我的 sqlite 扩展吗？

Answer 1

一种可能的解决方案是创建一个使用 ctypes 加载的库。

_{在这种情况下，我展示了 ubuntu Linux 的解决方案，但我认为类似的步骤可以应用于其他操作系统。}

编译库

qsqlite.pro

QT -= gui
QT += sql
TEMPLATE = lib
DEFINES += QSQLITE_LIBRARY
CONFIG += unversioned_libname unversioned_soname
CONFIG += c++11
SOURCES += 
qsqlite.cpp
HEADERS += 
qsqlite_global.h 
qsqlite.h
LIBS += -lsqlite3

qsqlite_global.h

#ifndef QSQLITE_GLOBAL_H
#define QSQLITE_GLOBAL_H
#if defined(_MSC_VER) || defined(WIN64) || defined(_WIN64) || defined(__WIN64__) || defined(WIN32) || defined(_WIN32) || defined(__WIN32__) || defined(__NT__)
#  define Q_DECL_EXPORT __declspec(dllexport)
#  define Q_DECL_IMPORT __declspec(dllimport)
#else
#  define Q_DECL_EXPORT     __attribute__((visibility("default")))
#  define Q_DECL_IMPORT     __attribute__((visibility("default")))
#endif
#if defined(QSQLITE_LIBRARY)
#  define QSQLITE_EXPORT Q_DECL_EXPORT
#else
#  define QSQLITE_EXPORT Q_DECL_IMPORT
#endif
#endif // QSQLITE_GLOBAL_H

Qsqlite.h

#ifndef QSQLITE_H
#define QSQLITE_H
#include "qsqlite_global.h"
class QSqlDriver;
extern "C" {
bool QSQLITE_EXPORT enable_extension(QSqlDriver *ptr, bool enabled);
}
#endif // QSQLITE_H

Qsqlite.cpp

#include "qsqlite.h"
#include <sqlite3.h>
#include <QSqlDriver>
#include <QVariant>
bool enable_extension(QSqlDriver *driver, bool enabled)
{
if(!driver)
return false;
QVariant v = driver->handle();
if (!v.isValid() || !(qstrcmp(v.typeName(), "sqlite3*")==0))
return false;
if(sqlite3 *db_handle = *static_cast<sqlite3 **>(v.data())){
sqlite3_initialize();
sqlite3_enable_load_extension(db_handle, enabled);
return true;
}
return false;
}

qsqlite/
├── qsqlite.cpp
├── qsqlite_global.h
├── qsqlite.h
└── qsqlite.pro

要编译，您必须使用 Qt，因此在这种情况下，我将通过执行以下命令使用 aqtinstall(python -m pip install aqtinstall

(：

python -m aqt install 5.15.0 linux desktop --outputdir qt
qt/5.15.0/gcc_64/bin/qmake qsqlite
make

注意：要编译库，必须具有sqlite3的标头，因此您必须在ubuntu中安装libsqlite3-dev：sudo apt install -y --no-install-recommends libsqlite3-dev。

这将创建必须在脚本旁边复制的 libqsqlite.so 库，例如以下代码加载空间模块(sudo apt install -y --no-install-recommends libsqlite3-mod-spatialite(。

main.py

from ctypes import CDLL, c_void_p
import os
from PyQt5.QtSql import QSqlDatabase, QSqlQuery
import sip
CURRENT_DIR = os.path.dirname(os.path.realpath(__file__))

def load_spatialite():
queries = (
"SELECT load_extension('mod_spatialite')",
"SELECT InitSpatialMetadata(1)",
)
q = QSqlQuery()
for query in queries:
if not q.exec_(query):
print(
f"Error: cannot load the Spatialite extension ({q.lastError().text()})"
)
return False
return True

def main():
db = QSqlDatabase.addDatabase("QSQLITE")
db.setDatabaseName("foo.sqlite")
if not db.open():
sys.exit(-1)
lib = CDLL(os.path.join(CURRENT_DIR, "libqsqlite.so"))
lib.enable_extension(c_void_p(sip.unwrapinstance(db.driver()).__int__()), True)
load_spatialite()
query = QSqlQuery()
query.exec_("CREATE TABLE my_line(id INTEGER PRIMARY KEY)")
query.exec_(
"""SELECT AddGeometryColumn("my_line","geom" , 4326, "LINESTRING", 2)"""
)
polygon_wkt = "POLYGON ((11 50,11 51,12 51,12 50,11 50))"
XA = 11
YA = 52
XB = 12
YB = 49
line_wkt = "LINESTRING({0} {1}, {2} {3})".format(XA, YA, XB, YB)
query.prepare("""INSERT INTO my_line VALUES (?,GeomFromText(?, 4326))""")
query.addBindValue(1)
query.addBindValue(line_wkt)
query.exec_()
query.prepare(
"""SELECT astext(st_intersection(geom, GeomFromText(?, 4326))) from my_line WHERE st_intersects(geom, GeomFromText(?, 4326))"""
)
query.addBindValue(polygon_wkt)
query.addBindValue(polygon_wkt)
query.exec_()
while query.next():
for i in range(query.record().count()):
print(query.value(i))

if __name__ == "__main__":
main()

├── main.py
└── libqsqlite.so

输出：

LINESTRING(11.333333 51, 11.666667 50)

---

相同的库可用于 PySide2：

from ctypes import CDLL, c_void_p
import os
from PySide2.QtSql import QSqlDatabase, QSqlQuery
import shiboken2
CURRENT_DIR = os.path.dirname(os.path.realpath(__file__))

def load_spatialite():
queries = (
"SELECT load_extension('mod_spatialite')",
"SELECT InitSpatialMetadata(1)",
)
q = QSqlQuery()
for query in queries:
if not q.exec_(query):
print(
f"Error: cannot load the Spatialite extension ({q.lastError().text()})"
)
return False
return True

def main():
db = QSqlDatabase.addDatabase("QSQLITE")
db.setDatabaseName("foo.sqlite")
if not db.open():
sys.exit(-1)
lib = CDLL(os.path.join(CURRENT_DIR, "libqsqlite.so"))
lib.enable_extension(c_void_p(shiboken2.getCppPointer(db.driver())[0]))
load_spatialite()
query = QSqlQuery()
query.exec_("CREATE TABLE my_line(id INTEGER PRIMARY KEY)")
query.exec_(
"""SELECT AddGeometryColumn("my_line","geom" , 4326, "LINESTRING", 2)"""
)
polygon_wkt = "POLYGON ((11 50,11 51,12 51,12 50,11 50))"
XA = 11
YA = 52
XB = 12
YB = 49
line_wkt = "LINESTRING({0} {1}, {2} {3})".format(XA, YA, XB, YB)
query.prepare("""INSERT INTO my_line VALUES (?,GeomFromText(?, 4326))""")
query.addBindValue(1)
query.addBindValue(line_wkt)
query.exec_()
query.prepare(
"""SELECT astext(st_intersection(geom, GeomFromText(?, 4326))) from my_line WHERE st_intersects(geom, GeomFromText(?, 4326))"""
)
query.addBindValue(polygon_wkt)
query.addBindValue(polygon_wkt)
query.exec_()
while query.next():
for i in range(query.record().count()):
print(query.value(i))

if __name__ == "__main__":
main()

_{对于测试，我使用了您可以在此处找到的 docker。}