c++ - QSqlError ("", "", "")

Question

我想为我的客户端服务器程序编写 SQLite 数据库。在数据库中，服务器应该保存来自客户端的每条消息。该表有 3 列:客户端 IP、日期和消息。我编写了以下代码，但在 insertmessage() 调试期间出现此错误:“QSqlError(”, “”, “”) ”。它有什么问题？我应该有一些代码来连接服务器收到的消息或客户端 IP 与数据库吗？非常感谢。

bool MainWindow::createConnection()
{

QSqlDatabase database = QSqlDatabase::addDatabase("QSQLITE");

database.setDatabaseName("Message.dat");

   if(!database.open())
   {
       qDebug()<<"can not open database";

       database.lastError().text();

       return false;
    }
   return true;
}

MainWindow::messagewindow()
{
     enum {
          messages_id = 0 ,
          messages_date =1 ,
          messages_HostAddreess = 2,
          messages_message = 3,
          };



      model = new QSqlTableModel(this);
     {
        model->setTable("messages");
        model->setHeaderData(messages_date, Qt::Horizontal, tr("Date"));
        model->setHeaderData(messages_HostAddreess, Qt::Horizontal, tr("From"));
        model->setHeaderData(messages_message, Qt::Horizontal, tr("Message"));
        model->select();

     }



     view = new QTableView;
     {
        view->setSelectionMode(QAbstractItemView::SingleSelection);
        view->setSelectionBehavior(QAbstractItemView::SelectRows);
        view->setColumnHidden(messages_id, true);
        view->setModel(model);
        view->resizeColumnsToContents();
        view->setEditTriggers(QAbstractItemView::NoEditTriggers);

        QHeaderView *header = view->horizontalHeader();
        header->setStretchLastSection(true);
     }

 }

 MainWindow::~MainWindow()
 {
  delete ui;
  }

---

  QString HostAddrress;
  QDate currentDate;
  QString message;

bool create =QFile::exists("Message.dat");
if (!myserver.createConnection())
   return 1;

if (create)

   myserver.createdata();

   myserver.insertMessage( HostAddrress, currentDate, message);


myserver.show();

return a.exec();

}

---

void MainWindow::createdata()
{
    QSqlQuery query;
    query.exec("DROP TABLE messages");
    query.exec("CREATE TABLE messages("
               "id INTEGER PRIMARY KEY AUTOINCREMENT,"
               "HostAddress varchar(20),"
               "date varchar(10),"
               "message varchar(30))");
}


void MainWindow::insertMessage(QString HostAddrress, QDate currentDate, QString message)
{
    QSqlQuery query;

    query.prepare("INSERT INTO messages(HostAddress, date, message) values(?,?,?)");

    query.addBindValue(HostAddrress);
    query.addBindValue(currentDate);
    query.addBindValue(message);
    query.exec();

    if (query.exec()) {
      // got no error, proceed
      qDebug() << "yes!";
    } else {
      // got an error, deal with it
      qDebug() << query.executedQuery();
      qDebug() << query.lastError();
    }
 }

Answer 1

你不需要像上面评论的那样让数据库成为类成员。但是当你创建你的 QSqlQuery 时，你应该像这样在构造函数中设置数据库

QSqlQuery query(QSqlDatabase::database());