PyQt5 QtSql 在QThread中访问数据库

Question

好的，既然我已经在 MDI 应用程序中弄清楚了整个持久性 QSqlDatabase，我试图在 QThread 中访问它：

class LoadWorker(QThread):
    totalSignal = pyqtSignal(int)
    countSignal = pyqtSignal(int)

    def __init__(self, parent=None):
        super(LoadWorker, self).__init__(parent)
        self.threadActive = True
        self.commitsize = 200
        self.filename = ""

    def run(self):
        query = QSqlQuery()
        query.exec("DELETE FROM mytable")
        #rest of code here

当运行时，我得到一个错误：

QSqlDatabasePrivate::database: requested database does not belong to the calling thread.
QSqlQuery::exec: database not open

一些研究表明我应该为线程启动一个新的数据库连接，所以我做了以下更改：

class LoadWorker(QThread):
    totalSignal = pyqtSignal(int)
    countSignal = pyqtSignal(int)

    def __init__(self, parent=None):
        super(LoadWorker, self).__init__(parent)
        self.threadActive = True
        self.commitsize = 200
        self.filename = ""
        self.database = QSqlDatabase.addDatabase('QSQLITE',"loader")
        if self.database:
            self.database.setDatabaseName("database/clireports.db")
        else:
            QMessageBox.critical(None, "Database Error", "Unable To Connect To The Database!")
            self.stop()

    def run(self):
        query = QSqlQuery()
        query.exec("DELETE FROM mytable")
        #rest of code here

但是，我仍然遇到同样的错误。我需要做些什么吗？

修改后的代码：

class LoadWorker(QThread):
    totalSignal = pyqtSignal(int)
    countSignal = pyqtSignal(int)

    def __init__(self, parent=None):
        super(LoadWorker, self).__init__(parent)
        self.threadActive = True
        self.commitsize = 200
        self.filename = ""

    def run(self):
        database = QSqlDatabase.addDatabase("QSQLITE","loader")
        database.setDatabaseName("database/clireports.db") # <---
        if not database.open():
            print("Database Error","Unable to connect to the database!")
            self.stop()

        # database.setDatabaseName("database/clireports.db")
        query = QSqlQuery()
        query.exec("DELETE FROM mytable")

未编辑代码：

class LoadWorker(QThread):
    totalSignal = pyqtSignal(int)
    countSignal = pyqtSignal(int)

    def __init__(self, parent=None):
        super(LoadWorker, self).__init__(parent)
        self.threadActive = True
        self.commitsize = 200
        self.filename = ""

    def run(self):
        database = QSqlDatabase.addDatabase("QSQLITE","loader")
        database.setDatabaseName("database/clireports.db")
        if not database.open():
            print("Database Error","Unable to connect to the database!")
            self.stop()
        query = QSqlQuery()
        query.exec("DELETE FROM cptdata")
        with open(self.filename, 'r', encoding="ISO-8859-1") as f:
            reader = csv.reader(f,delimiter='\t')
            data = list(reader)
            self.totalSignal.emit(len(data))
            f.close()
            counter = 0
            query.exec_("BEGIN TRANSACTION")
            for row in data:
                if self.threadActive == False: break
                counter +=1
                self.countSignal.emit(counter)
                if len(row) < 3: continue
                if "/" in row[0] or "Code" in row[0]: continue
                recordid = str(uuid.uuid1())
                cptcode = row[0].strip().upper()
                formatcode = cptcode[:5]
                description = row[2].strip().upper()
                if cptcode == "": continue
                query.prepare("INSERT INTO cptdata (recordid,cptcode,description) VALUES(:recordid,:cptcode,:description)")
                query.bindValue(":recordid", str(recordid))
                query.bindValue(":cptcode", str(formatcode))
                query.bindValue(":description", str(description))
                if query.exec_():
                    if counter % 200==0:
                        database.commit()
                        query.exec_("BEGIN TRANSACTION")
                database.commit()

    def stop(self):
        self.threadActive = False
        self.wait()


class CptLoader(QDialog):
    def __init__(self, parent=None):
        super(CptLoader, self).__init__(parent)
        loadUi("GlobalUI/fileloader.ui", self)

    def beginLoad(self,filename):
        self.thread = LoadWorker(self)
        self.thread.filename = filename
        self.thread.totalSignal.connect(self.prgLoader.setMaximum)
        self.thread.countSignal.connect(self.prgLoader.setValue)
        self.thread.start()

Answer 1

你必须相信 QSqlDatabase 在你想要工作的线程中，你不能将它移动到另一个线程所以你必须为你想要数据库使用的每个线程创建一个新连接。

另一方面，QThread 不是线程，而是它创建的线程的处理程序，因此构造方法属于创建 QThread 对象的线程，不同于处理 QThread 的线程在 run() 方法中执行，总之，如果要在该方法中使用它，则必须在运行方法中创建连接。

另一方面，您不能从另一个线程创建 GUI，在您的情况下，我看到您想从另一个线程显示带有 QMessageBox 的消息，这在 Qt 中是被禁止的。

示例：

from PyQt5 import QtCore, QtSql

class LoadWorker(QtCore.QThread):
    def run(self):
        database = QtSql.QSqlDatabase.addDatabase('QSQLITE')
        database.setDatabaseName("database/clireports.db")
        if not database.open():
            print("Database Error", "Unable To Connect To The Database!")
            self.stop()
        else:
            print("select")
            query = QtSql.QSqlQuery("SELECT * FROM mytable")
            rec = query.record()
            while query.next():
                for i in range(rec.count()):
                    print(query.value(i))

            print("delete")
            query.exec_("DELETE FROM mytable")

            print("select")
            query = QtSql.QSqlQuery("SELECT * FROM mytable")
            rec = query.record()
            while query.next():
                for i in range(rec.count()):
                    print(query.value(i))

    def stop(self):
        self.quit()
        self.wait()

if __name__ == '__main__':
    import sys

    app = QtCore.QCoreApplication(sys.argv)

    mthread = LoadWorker()
    mthread.start()
    sys.exit(app.exec_())

PyQt5 QtSql 在QThread中访问数据库

PyQt5 QtSql access database in QThread

python

pyqt

python-3.x

pyqt5

qsqldatabase