QT using SQLite database

1、 initialization

void Widget::InitialSQLiteDb()
{
    
    QSqlDatabase m_dbSystemData ;
//  Check the connected mode  -  Default connection name 
// QSqlDatabase::contains(QSqlDatabase::defaultConnection)
// if(QSqlDatabase::contains("qt_sql_default_connection"))
// {
    

// db = QSqlDatabase::database("qt_sql_default_connection");
// }
// else
// {
    
// db = QSqlDatabase::addDatabase("QSQLITE");
// }

    // Check the connected mode  -  Custom connection name 
    if(QSqlDatabase::contains("mysql_connection"))
    {
    

        m_dbSystemData = QSqlDatabase::database("mysql_connection");
    }
    else
    {
    
        m_dbSystemData = QSqlDatabase::addDatabase("QSQLITE","mysql_connection");
    }

    // Set the database path , Create if it does not exist 
    m_dbSystemData.setDatabaseName("mySysData.db");
    //db.setUserName();

    // Open database 
    if(!m_dbSystemData.open())
    {
    
        qDebug()<<"create sqldb failed!";
        return;
    }

    // Close the database 
    m_dbSystemData.close();
}

2、 Create a table

void Widget::CreateTable()
{
    
    if(!m_dbSystemData.isOpen())
    {
    
        qDebug()<<"db is not open!";
        return;
    }

    // Create... If it doesn't exist my_table surface  id Self increasing ,name only 
    const QString sql=R"( CREATE TABLE IF NOT EXISTS my_table ( id INTEGER PRIMARY KEY AUTOINCREMENT NOT NULL, code INTEGER, name CHAR (50) UNIQUE NOT NULL, age INTEGER, sex INTEGER, score INTEGER, rank INTEGER, address CHAR (50) );)";

    //QSqlQuery Pre tectonic , need db Opened and connected ; Not specified db perhaps db Use the default connection when it is invalid 
    QSqlQuery query(m_dbSystemData);

    if(query.exec(sql))
    {
    
        qDebug()<<"create table success!";
    }
    else
    {
    
        // Print sql Statement error message 
        qDebug()<<"create table error!"<< query.lastError();
    }
}

3、 insert data

void Widget::insertRecord(const QString &name, const QString address, int code, int age, int sex, int score, int rank)
{
    
    if(!m_dbSystemData.isOpen())
    {
    
        qDebug()<<"db is not open!";
        return;
    }

    qDebug()<<"2222!";

    QSqlQuery query(m_dbSystemData);

    // Mode one , Direct execution SQL sentence 
    query.exec(QString(R"(INSERT INTO my_table(code,name,age,sex,score,rank,address) VALUES(%1,'%2',%3,%4,%5,%6,'%7');)")
               .arg(code).arg(name).arg(age).arg(sex).arg(score).arg(rank).arg(address));

    // Mode two , Binding value , Undetermined variables are occupied by question marks by default , Notice that the string also has no quotation marks 
    /*query.prepare(R"(INSERT INTO my_table(name,age) VALUES(?,?);)"); query.addBindValue(name); query.addBindValue(age); query.exec();*/
}

4、 Delete data

void Widget::deleteRecord(const QString &name)
{
    
    if(!m_dbSystemData.isOpen())
    {
    
        qDebug()<<"db is not open!";
        return;
    }

    QSqlQuery query(m_dbSystemData);
    // Mode one , Direct execution SQL sentence 
    query.exec(QString(R"(DELETE FROM my_table WHERE name='%1';)").arg(name));

    // Mode two , Binding value , Undetermined variables are occupied by question marks by default 
    /*query.prepare(R"(DELETE FROM my_table WHERE name=?;)"); query.addBindValue(name); query.exec();*/
}

5、 Update data

void Widget::updateRecord(const QString &name, int age)
{
    
    if(!m_dbSystemData.isOpen())
    {
    
        qDebug()<<"db is not open!";
        return;
    }

    QSqlQuery query(m_dbSystemData);
    // Mode one , Direct execution SQL sentence 
    query.exec(QString(R"(UPDATE my_table SET age=%2 WHERE name='%1';)")
               .arg(name).arg(age));
    // Mode two , Binding value , Pending variable default question mark , Customizable 
    /*query.prepare(R"(UPDATE my_table SET age=:age WHERE name=:name;)"); query.bindValue(":name",name);// Replace with a custom alias  query.bindValue(":age",age); query.exec();*/
}

6、 Query data

int Widget::searchRecord(const QString &name)
{
    
    if(!m_dbSystemData.isOpen())
    {
    
        qDebug()<<"db is not open!";
        return -1;
    }

    QSqlQuery query(m_dbSystemData);
    query.exec(QString(R"(SELECT age FROM my_table WHERE name='%1';)").arg(name));

    // Get the... Of query results 0 It's worth ,
    // If the result is multiple rows of data , You can use while(query.next()){} Go through every line 
    int ageValue=-1;
    if(query.next())
    {
    
        ageValue = query.value(0).toInt();
    }
    qDebug()<<"age value is: "<< ageValue;
    return ageValue;
}

7、 Initialize table data

void Widget::InitialQTable()
{
    
    if(!m_dbSystemData.isOpen())
    {
    
        qDebug()<<"db is not open!";
        return;
    }

    ui->tableWidget->setColumnCount(7);
    //ui->tableWidget->setRowCount(10);
    ui->tableWidget->verticalHeader()->setVisible(false);  // Hide the list header 
    ui->tableWidget->horizontalHeader()->setStretchLastSection(true);
    ui->tableWidget->setSelectionBehavior(QAbstractItemView::SelectRows); // The way the whole line is selected 
    QStringList header;
    header<<" Student number "<<" full name "<<" Age "<<" Gender "<<" Total score "<<" ranking "<<" Address ";
    ui->tableWidget->setHorizontalHeaderLabels(header);

    QSqlQuery query(m_dbSystemData);
    query.exec("SELECT * FROM my_table");

    // If the result is multiple rows of data , You can use while(query.next()){} Go through every line 
    int nRow = 0;
    while(query.next())
    {
    
        int iRow = ui->tableWidget->rowCount();
        ui->tableWidget->setRowCount(iRow + 1);
        int id = query.value(0).toInt();
        QString code = query.value(1).toString();
        QString name = query.value(2).toString();
        QString age = query.value(3).toString();
        int nSex = query.value(4).toInt();
        QString sex;
        if(nSex == 0)
        {
    
            sex = " male ";
        }
        else
        {
    
            sex = " Woman ";
        }
        QString score = query.value(5).toString();
        QString rank = query.value(6).toString();
        QString address = query.value(7).toString();

        qDebug()<< id << code << name << age << sex << score << rank;

        ui->tableWidget->setItem(nRow,0,new QTableWidgetItem(code));
        ui->tableWidget->setItem(nRow,1,new QTableWidgetItem(name));
        ui->tableWidget->setItem(nRow,2,new QTableWidgetItem(age));
        ui->tableWidget->setItem(nRow,3,new QTableWidgetItem(sex));
        ui->tableWidget->setItem(nRow,4,new QTableWidgetItem(score));
        ui->tableWidget->setItem(nRow,5,new QTableWidgetItem(rank));
        ui->tableWidget->setItem(nRow,6,new QTableWidgetItem(address));

        nRow++;
    }

    ui->tableWidget->show();
}