Question

我第二次尝试连接数据库时收到此消息：

QSqlDatabasePrivate::removeDatabase: connection 'CompanyDatabase' is still in use, all queries will cease to work.

我删除了之前使用的模型，删除了所有连接，并关闭了数据库。下面我已经包含了打开CompanyWidget作为模式对话框的小部件，因为我认为我打开/关闭使用数据库的小部件可能是相关的。任何人解释为什么这个数据库仍然在使用？

编辑：如果我将QSqlDatabase成员更改为指针并使用以下命令创建它：

this->CompanyDatabase = new QSqlDatabase(QSqlDatabase::addDatabase("QSQLITE", "CompanyDatabase"));

并在重新添加数据库之前将其删除：

  if(this->CompanyDatabase)
    {
    delete this->CompanyDatabase;
    this->CompanyDatabase = NULL;
    }

然后错误就消失了。为什么这与我使用非指针成员的方式有什么不同？

EditCompanyWidget.h

#ifndef EditCompanyWidget_H
#define EditCompanyWidget_H

#include "ui_EditCompanyWidget.h"

#include <QDialog>
#include <QSqlDatabase>

class QSqlTableModel;


class EditCompanyWidget : public QDialog, private Ui::EditCompanyWidget
{
Q_OBJECT
public:

  EditCompanyWidget(QSqlDatabase);
  ~EditCompanyWidget();

public slots:

  void on_btnExit_clicked();

protected:
  QSqlTableModel* Model;
};

#endif

EditCompanyWidget.cpp

#include "EditCompanyWidget.h"

#include <iostream>

#include <QSqlDatabase>
#include <QStringList>
#include <QSqlQuery>
#include <QDebug>
#include <QSqlError>
#include <QVariant>
#include <QSqlTableModel>
#include <QSqlRecord>

EditCompanyWidget::EditCompanyWidget(QSqlDatabase database) : QDialog(NULL)
{
  setupUi(this);

  //QSqlTableModel* model = new QSqlTableModel;
  this->Model = new QSqlTableModel(NULL, database);
  this->Model->setTable("CompanyTable");
  this->Model->setEditStrategy(QSqlTableModel::OnManualSubmit);
  //model->setFilter(QString("id=%1").arg(1));
  this->Model->select();

  this->tableView->setModel(this->Model);
}

EditCompanyWidget::~EditCompanyWidget()
{
  if(this->Model)
    {
    std::cout << "destructor Deleting..." << std::endl;
    delete this->Model;
    this->Model = NULL;
    }
}


void EditCompanyWidget::on_btnExit_clicked()
{
  this->Model->revertAll();
  if(this->Model)
    {
    std::cout << "btnExit Deleting..." << std::endl;
    delete this->Model;
    this->Model = NULL;
    }
  //this->setResult(QDialog::Rejected);
  this->reject();
}

MainWidget.h

#ifndef TimeTrackerConfigurationWidget_H
#define TimeTrackerConfigurationWidget_H

#include "ui_TimeTrackerConfigurationWidget.h"

#include <QMainWindow>
#include <QSqlDatabase>

class TimeTrackerConfigurationWidget : public QMainWindow, private Ui::TimeTrackerConfigurationWidget
{
Q_OBJECT
public:
  TimeTrackerConfigurationWidget(QWidget *parent = 0);

public slots:
  void on_btnNewCompany_clicked();
  void on_btnEditCompany_clicked();

protected:
  QSqlDatabase CompanyDatabase;
};

#endif

MainWidget.cpp

#include "TimeTrackerConfigurationWidget.h"

#include "EditCompanyWidget.h"

#include <iostream>

#include <QSqlDatabase>
#include <QFileDialog>
#include <QSqlError>
#include <QSqlQuery>

TimeTrackerConfigurationWidget::TimeTrackerConfigurationWidget(QWidget *parent) : QMainWindow(parent)
{
  setupUi(this);
}


void TimeTrackerConfigurationWidget::on_btnEditCompany_clicked()
{
//   QString fileName = QFileDialog::getOpenFileName(this, "Database File", ".", "Image Files (*.sqlite)");
//
//   if(fileName.toStdString().empty())
//     {
//     std::cout << "Filename was empty." << std::endl;
//     return;
//     }

  QString fileName = "test.sqlite";

  if(!QFile::exists(fileName))
    {
    std::cerr << "File does not exist!" << std::endl;
    return;
    }

  this->CompanyDatabase.close();
  //QSqlDatabase::removeDatabase("CompanyDatabase");
  //QSqlDatabase database = QSqlDatabase::addDatabase("QSQLITE");

  // Delete all connections
  for(unsigned int i = 0; i < QSqlDatabase::connectionNames().size(); ++i)
    {
    //QSqlDatabase::removeDatabase("TestConnection");
    QSqlDatabase::removeDatabase(QSqlDatabase::connectionNames()[i]);
    }


  this->CompanyDatabase = QSqlDatabase::addDatabase("QSQLITE", "CompanyDatabase");
  //this->CompanyDatabase = QSqlDatabase::addDatabase("QSQLITE");
  this->CompanyDatabase.setDatabaseName(fileName);
  if (!this->CompanyDatabase.open())
    {
    std::cerr << "Could not open database" << std::endl;
    std::cerr << this->CompanyDatabase.lastError().text().toStdString() << std::endl;
    return;
    }

  EditCompanyWidget* editCompanyWidget = new EditCompanyWidget(this->CompanyDatabase);
  editCompanyWidget->exec();
  delete editCompanyWidget;
}

Answer 1

文档明确说明：http://doc.qt.io/qt-4.8/qsqldatabase.html#removeDatabase。在删除连接之前，必须销毁已实例化的所有查询对象和QSqlDatabase连接对象。当你删除指针时，你实际上是这样做的。使用之前的代码，你不是。

删除后，SQL连接仍然打开

1 个答案: