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

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

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1. 下面是创建数据库的操作，写成 createConnection()
   
2. bool database::createconnection()
   
3. {
   
4.     bool IsExist = QFile::exists("Myqq.dat");
   
5.     db = QSqlDatabase::addDatabase("QSQLITE"); // 注意不要拼写错误
   
6.     db.setDatabaseName("Myqq.dat");
   
7.     if (!db.open())
   
8.     {
   
9.         QMessageBox::critical(0, "Cannot open database",
   
10.             "Unable to establish a database connection./n"
    
11.                      "This example needs SQLite support. Please read "
    
12.                      "the Qt SQL driver documentation for information how "
    
13.                      "to build it./n/n"
    
14.                      "Click Cancel to exit.", QMessageBox::Cancel);
    
15.         return false;
    
16.     }
    
17.     if (!IsExist)
    
18.     {
    
19.         if (!createDatabase())
    
20.             return false;
    
21.     }
    
22.     return true;
    
23. }

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1. 下面是创建数据库的操作，写成 createConnection()
   
2. bool database::createconnection()
   
3. {
   
4.     bool IsExist = QFile::exists("Myqq.dat");
   
5.     db = QSqlDatabase::addDatabase("QSQLITE"); // 注意不要拼写错误
   
6.     db.setDatabaseName("Myqq.dat");
   
7.     if (!db.open())
   
8.     {
   
9.         QMessageBox::critical(0, "Cannot open database",
   
10.             "Unable to establish a database connection./n"
    
11.                      "This example needs SQLite support. Please read "
    
12.                      "the Qt SQL driver documentation for information how "
    
13.                      "to build it./n/n"
    
14.                      "Click Cancel to exit.", QMessageBox::Cancel);
    
15.         return false;
    
16.     }
    
17.     if (!IsExist)
    
18.     {
    
19.         if (!createDatabase())
    
20.             return false;
    
21.     }
    
22.     return true;
    
23. }

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1. 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。
   
2. bool database::createDatabase()
   
3. {
   
4.     QSqlQuery query;
   
5.     qDebug() << "Start to create table..."; // qDebut()方便在 debug 的时候查看
   
6.     //create table: User
   
7.     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]) )");
   
8.     //create table: Connect
   
9.     query.exec("CREATE TABLE [Connect] ( [LeftUser] VARCHAR(40) NOT NULL, [RightUser] VARCHAR(40) NOT NULL, [relation] INTEGER DEFAULT '0' NULL, PRIMARY KEY ([LeftUser], [RightUser]))");
   
10.     if (query.lastError().isValid())
    
11.     {
    
12.         qDebug() << query.lastError();
    
13.         return false;
    
14.     }
    
15.     else
    
16.     {
    
17.         qDebug() << "Create database successfully.";
    
18.     }
    
19.     return true;
    
20. }

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

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1. bool database::createDatabase()
   
2. {
   
3.     QSqlQuery query; // 此处请查询 query的相关操作
   
4.     qDebug() << "Start to create table...";
   
5.     //create table: User
   
6.     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
   
7.     //create table: Connect
   
8.     query.exec("CREATE TABLE [Connect] ( [LeftUser] VARCHAR(40) NOT NULL, [RightUser] VARCHAR(40) NOT NULL, [relation] INTEGER DEFAULT '0' NULL, PRIMARY KEY ([LeftUser], [RightUser]))");
   
9.     if (query.lastError().isValid())
   
10.     {
    
11.         qDebug() << query.lastError();
    
12.         return false;
    
13.     }
    
14.     else
    
15.     {
    
16.         qDebug() << "Create database successfully.";
    
17.     }
    
18.     return true;
    
19. }

插入操作

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1. bool database::adduser( User user )
   
2. {
   
3.     if (!db.isOpen())
   
4.     {
   
5.         createconnection();
   
6.     }
   
7.     QSqlQuery query;
   
8.     qDebug() << "start to insert data";
   
9.     query.exec("INSERT INTO [User] ( userId, username, email, password, city) VALUES(?,?,?,?,?)");
   
10.     QVariantList userId;
    
11.     userId << user.getUserId();
    
12.     query.addBindValue(userId);
    
13.     QVariantList username;
    
14.     username << user.getUserName();
    
15.     query.addBindValue(username);
    
16.     QVariantList email;
    
17.     email << user.getEmail();
    
18.     query.addBindValue(email);
    
19.     QVariantList password;
    
20.     password << user.getPassword();
    
21.     query.addBindValue(password);
    
22.     QVariantList city;
    
23.     city << user.getCity();
    
24.     query.addBindValue(city);
    
25.     try
    
26.     {
    
27.         if (!query.execBatch())
    
28.         {
    
29.             qDebug() << query.lastQuery();
    
30.             qDebug() << query.lastError();
    
31.             return NULL;
    
32.         }
    
33.     }
    
34.     catch(...)
    
35.     {
    
36.         QMessageBox::critical(0, "Add New Node error!",
    
37.                               "Unable to add a new Node!/n/n"
    
38.                                        "Click Cancel to exit.", QMessageBox::Cancel);
    
39.     }
    
40.     if( !UpdateConnectTable(user.getUserId(),user.getUserId(),2))
    
41.     {
    
42.         QMessageBox::critical(0,"","Update table Connect error");
    
43.         return NULL;
    
44.     }
    
45.     return true;
    
46. }