Qt--- DataBase

a database connection is represented by a QSqlDatabase object and to execute SQL queries, we must first establish a connection with a database.

  1. bool createConnection()  
  2. {  
  3.     QSqlDatabase db = QSqlDatabase::addDatabase("QMYSQL");  
  4.     db.setHostName("mozart.konkordia.edu");  
  5.     db.setDatabaseName("musicdb");  
  6.     db.setUserName("gbatstone");  
  7.     db.setPassword("T17aV44");  
  8.     if (!db.open()) {  
  9.         QMessageBox::critical(0, QObject::tr("Database Error"),  
 10.                               db.lastError().text());  
 11.         return false;  
 12.     }  
 13.     return true;  
 14. }  

if open() fails, we show an error message.

Once a connection is established, we can use QSqlQuery to execute any SQL statement that the underlying database supports

  1. QSqlQuery query;  
  2. query.exec("SELECT title, year FROM cd WHERE year >= 1998");  

We call next() once to position the QSqlQuery on the first record of the result set

if the result set is empty , the frist call to next() will return false

当然我们并不是所以内容都希望转换为string 类型的,而 prepare() 可以使用户使用指定的类型的变量,如果我们希望create multiple cconnections, we can pass a name as second argument to   addDatabase()

QSqlDatabase::addDatabase("QPSQL","OTHER");