QT 数据库创建，插入等简单操作

应用程序很多情况下需要操作数据库。QT支持多种数据库，但是很多情况需要安装DLL驱动。这就有点麻烦，想当初想用MYSQL的结果就

是因为驱动很难装，然后就使用了SQLITE。如果对数据库的要求不是很高的话，Sqlite应该可以满足需求了。下面就简单介绍下在QT中的

需要包含如下的数据库相关头文件：
#include <QSqlDatabase>
#include <QSqlQuery>

下面是创建数据库的操作，写成 createConnection()
bool database::createconnection()
{
    bool IsExist = QFile::exists("Myqq.dat");
    db = QSqlDatabase::addDatabase("QSQLITE"); // 注意不要拼写错误
    db.setDatabaseName("Myqq.dat");
    if (!db.open())
    {
        QMessageBox::critical(0, "Cannot open database",
            "Unable to establish a database connection./n"
                     "This example needs SQLite support. Please read "
                     "the Qt SQL driver documentation for information how "
                     "to build it./n/n"
                     "Click Cancel to exit.", QMessageBox::Cancel);
        return false;
    }
    if (!IsExist)
    {
        if (!createDatabase())
            return false;
    }
    return true;
}

下面是创建数据库的操作，写成 createConnection()
bool database::createconnection()
{
    bool IsExist = QFile::exists("Myqq.dat");
    db = QSqlDatabase::addDatabase("QSQLITE"); // 注意不要拼写错误
    db.setDatabaseName("Myqq.dat");
    if (!db.open())
    {
        QMessageBox::critical(0, "Cannot open database",
            "Unable to establish a database connection./n"
                     "This example needs SQLite support. Please read "
                     "the Qt SQL driver documentation for information how "
                     "to build it./n/n"
                     "Click Cancel to exit.", QMessageBox::Cancel);
        return false;
    }
    if (!IsExist)
    {
        if (!createDatabase())
            return false;
    }
    return true;
}

下面是创建数据库 createDatabase()。创建了两张表，最需要注意的就是：不要把数据库操作写错了，比如单词写错了。因为没有提示，所以还是蛮容易写错的。最后出错了，还不容易找到错误。
bool database::createDatabase()
{
    QSqlQuery query;
    qDebug() << "Start to create table..."; // qDebut()方便在 debug 的时候查看
    //create table: User
    query.exec("CREATE TABLE [User] ( [userId] VARCHAR(40) NOT NULL, [username] VARCHAR(40) NOT NULL, [email] VARCHAR(40), [password] VARCHAR(40), [city] VARCHAR(20), PRIMARY KEY([userId]) )");
    //create table: Connect
    query.exec("CREATE TABLE [Connect] ( [LeftUser] VARCHAR(40) NOT NULL, [RightUser] VARCHAR(40) NOT NULL, [relation] INTEGER DEFAULT '0' NULL, PRIMARY KEY ([LeftUser], [RightUser]))");
    if (query.lastError().isValid())
    {
        qDebug() << query.lastError();
        return false;
    }
    else
    {
        qDebug() << "Create database successfully.";
    }
    return true;
}

下面就简单的贴下自己写的 创建和插入的操作方法。会写数据库的童鞋知道语法了 就知道怎么写了

bool database::createDatabase()
{
    QSqlQuery query; // 此处请查询 query的相关操作
    qDebug() << "Start to create table...";
    //create table: User
    query.exec("CREATE TABLE [User] ( [userId] VARCHAR(40) NOT NULL, [username] VARCHAR(40) NOT NULL, [email] VARCHAR(40), [password] VARCHAR(40), [city] VARCHAR(20), PRIMARY KEY([userId]) )"); // 一定注意不要拼写错误，引号内是不提示拼写错误的。自己也感觉这有点不方便
    //create table: Connect
    query.exec("CREATE TABLE [Connect] ( [LeftUser] VARCHAR(40) NOT NULL, [RightUser] VARCHAR(40) NOT NULL, [relation] INTEGER DEFAULT '0' NULL, PRIMARY KEY ([LeftUser], [RightUser]))");
    if (query.lastError().isValid())
    {
        qDebug() << query.lastError();
        return false;
    }
    else
    {
        qDebug() << "Create database successfully.";
    }
    return true;
}

插入操作

bool database::adduser( User user )
{
    if (!db.isOpen())
    {
        createconnection();
    }
    QSqlQuery query;
    qDebug() << "start to insert data";
    query.exec("INSERT INTO [User] ( userId, username, email, password, city) VALUES(?,?,?,?,?)");
    QVariantList userId;
    userId << user.getUserId();
    query.addBindValue(userId);
    QVariantList username;
    username << user.getUserName();
    query.addBindValue(username);
    QVariantList email;
    email << user.getEmail();
    query.addBindValue(email);
    QVariantList password;
    password << user.getPassword();
    query.addBindValue(password);
    QVariantList city;
    city << user.getCity();
    query.addBindValue(city);
    try
    {
        if (!query.execBatch())
        {
            qDebug() << query.lastQuery();
            qDebug() << query.lastError();
            return NULL;
        }
    }
    catch(...)
    {
        QMessageBox::critical(0, "Add New Node error!",
                              "Unable to add a new Node!/n/n"
                                       "Click Cancel to exit.", QMessageBox::Cancel);
    }
    if( !UpdateConnectTable(user.getUserId(),user.getUserId(),2))
    {
        QMessageBox::critical(0,"","Update table Connect error");
        return NULL;
    }
    return true;
}