c++ - 处理 QSqlDatabase 连接

Question

处理 QSqlDatabase 连接的正确方法是什么？

在我的程序中我是这样做的:

DatabaseConnector *databaseConnector = 0;
try
{
    databaseConnector = new DatabaseConnector();
    //Do stuff...
    delete databaseConnector;
}
catch(QString e)
{
    delete databaseConnector;
    QMessageBox::information(this,"Error",e);
}

databaseConnector.h

#ifndef DATABASECONNECTOR_H
#define DATABASECONNECTOR_H
#include <QtSql>

class DatabaseConnector
{
public:
    DatabaseConnector();
    DatabaseConnector(QString hostname, QString database, QString user, QString password);
    ~DatabaseConnector();
private:
    QSqlDatabase db;
};

#endif // DATABASECONNECTOR_H

数据库连接器.cpp

#include "databaseconnector.h"
#include <QString>

DatabaseConnector::DatabaseConnector()
{
    QSettings settings;

    db = QSqlDatabase::addDatabase("QIBASE");
    db.setHostName(settings.value("db/host").toString());
    db.setDatabaseName(settings.value("db/name").toString());
    db.setUserName(settings.value("db/user").toString());
    db.setPassword(settings.value("db/pass").toString());

    if(!db.open())
    {
        QString databaseConnectionError = db.lastError().text();
        throw databaseConnectionError;
    }
}

DatabaseConnector::DatabaseConnector(QString hostname, QString database, QString user,     QString password)
{
    db = QSqlDatabase::addDatabase("QIBASE");
    db.setHostName(hostname);
    db.setDatabaseName(database);
    db.setUserName(user);
    db.setPassword(password);
    if(!db.open())
    {
        QString databaseConnectionError = db.lastError().text();
        throw databaseConnectionError;
    }

}

DatabaseConnector::~DatabaseConnector()
{
    db.close();
}

即使我使用 QSqlDatabase::removeDatabase(db.connectionName());

QSqlDatabasePrivate::addDatabase: duplicate connection name 'qt_sql_default_connection', old connection removed.

Answer 1

通常您不需要在应用程序中多次打开数据库连接。

添加数据库时，可以给连接命名:

QSqlDatabase::addDatabase( "QIBASE", "MyDBConnectionName" );

您可以使用名称来查询连接:

if( QSqlDatabase::contains( "MyDBConnectionName" ) )
{
    QSqlDatabase db = QSqlDatabase::database( "MyDBConnectionName" );
    //Do stuff...
}
else
{
    // connection not found, do something
}

另请注意，在调用 QSqlDatabase::removeDatabase 之前，您应该断开数据库连接:

db.close();
QSqlDatabase::removeDatabase("MyDBConnectionName");