Qt连接mysql数据库，全局变量定义db

#include "mainwindow.h" #include "ui_mainwindow.h" #include <QtSql> #include<QSqlError> #include <QDebug> QSqlDatabase db; //查询数据 QSqlQuery MainWindow::queryDatabase(const QString &query) { QSqlQuery sqlQuery; sqlQuery = QSqlQuery(db); if (!sqlQuery.exec(query)) { qDebug() << "查询失败：" << sqlQuery.lastError().text(); } return sqlQuery; } void MainWindow::queryDatabase1(){ QSqlQuery query=this->queryDatabase("select * from user"); /*while (query.next()) { QString result = query.value(0).toString(); QString result1 = query.value(1).toString(); qDebug() << result<<" "<<result1; }*/ QSqlQueryModel *model=new QSqlQueryModel(ui->tableView); model->setQuery(query);//将查询结果绑定到模型上 ui->tableView->setModel(model); } //连接数据库 bool MainWindow::connectToDatabase(const QString &host, const QString &dbName, const QString &user, const QString &password) { //db = QSqlDatabase::addDatabase("QMYSQL"); db.setHostName(host); db.setDatabaseName(dbName); db.setUserName(user); db.setPassword(password); if (!db.open()) { qDebug() << "数据库连接失败：" << db.lastError().text(); return false; } else { qDebug() << "数据库连接成功！"; return true; } } //点击按钮实现数据库表的数据删除 void MainWindow::onButtonClicked2() { QString username = ui->lineEdit_3->text(); QSqlQuery query; //QString username=ui->lineEdit->text(); //QSqlQuery query; QString str=QString("delete from user where username='%1'").arg(username); if (!query.exec(str)) { qDebug() << "删除失败：" << query.lastError().text(); } else { qDebug() << "删除成功"; } } //点击按钮实现表的数据的显示 void MainWindow::onButtonClicked1() { //QSqlDatabase db=QSqlDatabase::addDatabase("QMYSQL"); /*QString host="localhost"; QString dbName="sys"; QString user="root"; QString password="12345"; this->connectToDatabase(host,dbName,user,password);*/ QSqlQuery query=this->queryDatabase("select * from user"); /*while (query.next()) { QString result = query.value(0).toString(); QString result1 = query.value(1).toString(); qDebug() << result<<" "<<result1; }*/ QSqlQueryModel *model=new QSqlQueryModel(ui->tableView); model->setQuery(query);//将查询结果绑定到模型上 ui->tableView->setModel(model); } //点击按钮，实现查找某条数据 void MainWindow::onButtonClicked3() { /*QSqlDatabase db=QSqlDatabase::addDatabase("QMYSQL");*/ /*QString host="localhost"; QString dbName="sys"; QString user="root"; QString password="12345"; this->connectToDatabase(host,dbName,user,password);*/ QString username = ui->lineEdit_4->text(); QSqlQuery query=this->queryDatabase(QString("select * from user where username = '%1'").arg(username)); /*while (query.next()) { QString result = query.value(0).toString(); QString result1 = query.value(1).toString(); qDebug() << result<<" "<<result1; }*/ QSqlQueryModel *model=new QSqlQueryModel(ui->tableView); model->setQuery(query);//将查询结果绑定到模型上 ui->tableView->setModel(model); db.close(); } //跳转到增加数据框 void MainWindow::onButtonClicked4() { Dialog d(this); //d.setWindowFlags(Qt::CustomizeWindowHint | Qt::WindowCloseButtonHint); d.exec(); } //跳转到修改数据框 void MainWindow::onButtonClicked5() { Dialog1 d(this); //d.setWindowFlags(Qt::CustomizeWindowHint | Qt::WindowCloseButtonHint); d.exec(); } MainWindow::MainWindow(QWidget *parent) : QMainWindow(parent) , ui(new Ui::MainWindow) { ui->setupUi(this); //static QSqlDatabase db=QSqlDatabase::addDatabase("QMYSQL"); QString host="localhost"; QString dbName="sys"; QString user="root"; QString password="12345"; this->connectToDatabase(host,dbName,user,password); //this->queryDatabase1(db); connect(ui->pushButton_3, &QPushButton::clicked, this, &MainWindow::onButtonClicked5); connect(ui->pushButton_4, &QPushButton::clicked, this, &MainWindow::onButtonClicked3); connect(ui->pushButton, &QPushButton::clicked, this, &MainWindow::onButtonClicked1); connect(ui->pushButton_2, &QPushButton::clicked, this, &MainWindow::onButtonClicked2); connect(ui->pushButton_5, &QPushButton::clicked, this, &MainWindow::onButtonClicked4); /*QSqlQuery query=this->queryDatabase(db,"select * from user"); /*while (query.next()) { QString result = query.value(0).toString(); QString result1 = query.value(1).toString(); qDebug() << result<<" "<<result1; }*/ /*QSqlQueryModel *model=new QSqlQueryModel(ui->tableView); model->setQuery(query);//将查询结果绑定到模型上 ui->tableView->setModel(model); ui-> //ui->setupUi(this);*/ } MainWindow::~MainWindow() { delete ui; }