c++ - QSqlDatabase 检查数据库是否已经存在

Question

我需要在本地系统上存储一些值并稍后以表格格式访问它，所以我选择了 QSqlDatabase。首先我必须检查数据库是否已经存在。但是使用下面的代码我总是收到消息 Data base not exist creating new.... 可能是什么问题？

#include <QtCore/QCoreApplication>
#include <QtSql/QSqlDatabase>
#include "QFile"
#include "QDebug"

int main(int argc, char *argv[])
{
    QCoreApplication a(argc, argv);
    QString dbName = "lprDB";
    QSqlDatabase db = QSqlDatabase::addDatabase("QSQLITE");

    if( QFile::exists(dbName))
    {
         qDebug()<<"Data base exist....";
    }
    else {
        qDebug()<<"Data base not exist creating new....";
        db.setDatabaseName(dbName);
    }

    return a.exec();
}

Answer 1

如@Armatel 所述，您应该打开数据库，这将创建数据库文件。

#include <QtCore/QCoreApplication>  
#include <QtSql/QSqlDatabase>
#include "QFile"
#include "QDebug"

int main(int argc, char *argv[])
{
    QCoreApplication a(argc, argv);
    QString dbName = "lprDB";
    QSqlDatabase db = QSqlDatabase::addDatabase("QSQLITE");

    if( QFile::exists(dbName))
    {
        qDebug()<<"Data base exist....";
    }
    else {
        qDebug()<<"Data base not exist creating new....";
        db.setDatabaseName(dbName);
        db.open(); // <<< Add this!

        if(!db.isOpen()) {
            qDebug() << "ERROR: could not open database";
        }
        qDebug() << "DB opened";
    }

    return a.exec();
}