I started with c++ QT recently.
I created class "ControllerOfDB" to hold pointer to my QSqlDatabase and few functions (to make inserts/selects).
Example select function:
QList<data1> GetData1()
{
QList<data1> output;
if(!dataBase->isOpen())
dataBase->open();
if(dataBase->isOpen())
{
QSqlQuery* query = new QSqlQuery(*dataBase);
query->prepare("SELECT * FROM table1");
if(query->exec())
while (query->next())
{
output.append( *(new data1(
query->value(0).toInt(),
query->value(1).toString(),
query->value(2).toInt(),
query->value(3).toInt(),
query->value(4).toInt(),
)) );
}
query->clear();
query->finish();
delete query;
}
return output;
}
It was all working fine, until i had to add possibility to change db or login as different user. I modified Connect and Disconnect function. After few iterrations, this is what i get:
void Connect()
{
dataBase = new QSqlDatabase(QSqlDatabase::addDatabase("QPSQL", "Main"));
dataBase->setHostName(hostName);
dataBase->setPort(port);
dataBase->setDatabaseName(dbName);
dataBase->setUserName(userName);
dataBase->setPassword(userPass);
if(!dataBase->isOpen())
dataBase->open();
}
void Disconnect()
{
if(dataBase != NULL)
if(dataBase->isOpen()){
dataBase->close();
dataBase->removeDatabase("Main");
dataBase = NULL;
}
}
hostName, port, dbName, userName and userPass are also attributes of that class.
public:
QSqlDatabase *dataBase;
QString hostName;
int port;
QString dbName;
QString userName;
QString userPass;
whenever i try to diconnect and create new connection i recieve warnings/errors about queries of my current connections - even if i only "connected" ( = used function Connect() ).
I already saw few similar topics and documentation for it, saying i have to remove queries from scope, but at this point i don't know how.
when you look at QSqlDatabase document, the method removeDatabase is static, so your method Disconnect logic should be like:
void Disconnect()
{
if(dataBase != NULL) {
if(dataBase->isOpen()){
dataBase->close();
}
delete dataBase;
dataBase = NULL;
}
QSqlDatabase::removeDatabase("Main");
}
Related
I've made separate functions for open and close connection.But it wont let me to add new record on new form.
this is login header file.
public:
QSqlDatabase mydb;
void connClose()
{
//QString connection;
//connection = mydb.connectionName();
mydb.close();
//mydb.removeDatabase(connection);
mydb.removeDatabase(mydb.connectionName());
}
bool connOpen()
{
mydb=QSqlDatabase::addDatabase("QSQLITE");
mydb.setDatabaseName("./Poem.db");
if(mydb.open())
{
return true;
}
else if(!mydb.open())
{
return false;
}
}
this is the other form add button :
QString Title,Group,Poem;
Title = ui->lineEdit->text();
Group = ui->label_2->text();
Poem = ui->textEdit->toPlainText();
MainWindow mainwindow;
mainwindow.connOpen();
QSqlQuery * qry1 = new QSqlQuery(mainwindow.mydb);
qry1->prepare("insert into Poems(Title,Poem,Group) values ('"+Title+"','"+Poem+"','"+Group+"')");
if(qry1->exec())
{
QMessageBox::critical(this,tr("درج شعر جدید"),tr("شعر اضافه شد"));
mainwindow.connClose();
}
I get this errors :
duplicate connection name 'qt_sql_default_connection', old connection removed.
connection 'qt_sql_default_connection' is still in use, all queries will cease to work.
You are committing exactly what Qt QSqlDatabase Documentation warns about:
Warning: There should be no open queries on the database connection
when this function is called
...
// WRONG
QSqlDatabase db = QSqlDatabase::database("sales");
QSqlQuery query("SELECT NAME, DOB FROM EMPLOYEES", db);
QSqlDatabase::removeDatabase("sales"); // will output a warning
// "db" is now a dangling invalid database connection, // "query"
contains an invalid result set
and the correct is:
{
QSqlDatabase db = QSqlDatabase::database("sales");
QSqlQuery query("SELECT NAME, DOB FROM EMPLOYEES", db);
}
// Both "db" and "query" are destroyed because they are out of scope
QSqlDatabase::removeDatabase("sales"); // correct
So in your case you execute query qry1 and remove the database within same scope (i.e before qry1 goes out of scope), you should modify your code to make sure qry1 is executed and gets destroyed / goes out of scope / before deleting the database. Try this:
{
QSqlQuery * qry1 = new QSqlQuery(mainwindow.mydb);
qry1->prepare("insert into Poems(Title,Poem,Group) values ('"+Title+"','"+Poem+"','"+Group+"')");
if(qry1->exec())
{
QMessageBox::critical(this,tr("درج شعر جدید"),tr("شعر اضافه شد"));
}
}
mainwindow.connClose();
I have a folder where i have a many databases. Some times may be deleted or added database to the folder.
So I use QTimer and read all databases.
It is a my code:
this->timer = new QTimer(this);
this->timer->setInterval(15000);
connect(this->timer, &QTimer::timeout, this, [=]() {
QString path = "C:\\Users\\User\\Desktop\\DAXI SMS SENDER\\SMSSenderAllBASE";
//QString path = qApp->applicationDirPath() + "\\SMSSenderAllBASE";
QDir recoredDir(path);
QStringList allFiles = recoredDir.entryList(QDir::NoDotAndDotDot | QDir::System | QDir::Hidden | QDir::AllDirs | QDir::Files, QDir::DirsFirst);
for (int i = 0; i < allFiles.size(); i++) {
QString fullPath = path + "\\" + allFiles[i];
QString connectionName = allFiles[i];
connectionName = connectionName.remove(connectionName.size() - 4, 4);
QSqlDatabase db = QSqlDatabase::addDatabase("QIBASE", connectionName);
db.setDatabaseName(fullPath);
db.setHostName("localhost");
db.setPort(3050);
db.setUserName("SYSDBA");
db.setPassword("masterkey");
thrdHelperSendSMS *help = new thrdHelperSendSMS(db, this);
connect(help, &thrdHelperSendSMS::helperFinished, this, [=](QString connectionName){
QSqlDatabase t_db = QSqlDatabase::database(connectionName);
t_db.close();
QSqlDatabase::removeDatabase(connectionName);
delete help;
});
help->run();
}
});
this->timer->start();
Yes I'm sure that the helperFinished signal will happen and this time I will not have any connection with this base.
EDIT:
If i remove
thrdHelperSendSMS *help = new thrdHelperSendSMS(db, this);
connect(help, &thrdHelperSendSMS::helperFinished, this, [=](QString connectionName){
QSqlDatabase t_db = QSqlDatabase::database(connectionName);
t_db.close();
QSqlDatabase::removeDatabase(connectionName);
delete help;
});
help->run();
example:
for (int i = 0; i < allFiles.size(); i++) {
QString fullPath = path + "\\" + allFiles[i];
QString connectionName = allFiles[i];
connectionName = connectionName.remove(connectionName.size() - 4, 4);
QSqlDatabase db = QSqlDatabase::addDatabase("QIBASE", connectionName);
db.setDatabaseName(fullPath);
db.setHostName("localhost");
db.setPort(3050);
db.setUserName("SYSDBA");
db.setPassword("masterkey");
QSqlDatabase::removeDatabase(connectionName);
}
I have the same error.
You don't use removeDatabase() correctly. The object of SqlDatabase needs to go out of scope first. See documentation.
Wrong use
QSqlDatabase db = QSqlDatabase::database("sales");
QSqlQuery query("SELECT NAME, DOB FROM EMPLOYEES", db);
QSqlDatabase::removeDatabase("sales"); // will output a warning
Correct use
{
QSqlDatabase db = QSqlDatabase::database("sales");
QSqlQuery query("SELECT NAME, DOB FROM EMPLOYEES", db);
}
// Both "db" and "query" are destroyed because they are out of scope
QSqlDatabase::removeDatabase("sales"); // correct
In the second example db will go out of scope after } and you will no longer see the error message QSqlDatabasePrivate::removeDatabase: connection 'myConnectionName' is still in use, all queries will cease to work
Please read the documentation carefully. The database stuff is sensible and every line needs to be checked carefully.
Also you have missing db.close(); - It makes sense to close the database before you remove it.
#user3606329's answer is right, but I add this possibility:
QSqlDatabase db = QSqlDatabase::database("sales");
{
QSqlQuery query("SELECT NAME, DOB FROM EMPLOYEES", db);
//use query
}
db = QSqlDatabase();
QSqlDatabase::removeDatabase("sales");
You can use std::swap to force it destruct on demand.
I basically use BOOST_SCOPE_EXIT for cases when want to call a function on scope exit including not expected exit like through an exception throw.
#include <boost/scope_exit.hpp>
{
QSqlDatabase db;
BOOST_SCOPE_EXIT(this_, &db) { // by reference, otherwise it will copy a stack object
// access object here through the this_ instead of this ...
if (db.isOpen()) {
db.close(); // closing if not yet closed before connection remove
}
std::swap(db, QSqlDatabase{}); // destruct via swap
// CAUTION:
// From this point you must not call to `QSqlDatabase::database("MYDB", ...)`, otherwise it will return another constructed object!
//
QSqlDatabase::removeDatabase("MYDB");
} BOOST_SCOPE_EXIT_END
// ui change from here ...
// accomplish last ui changes before long blocking operation
qApp->processEvents();
db = QSqlDatabase::addDatabase("...", "MYDB");
// database access from here ...
}
QSqlDatabase db = QSqlDatabase::addDatabase("QSQLITE", "conn_name");
db.open();
if (db.open())
{
qDebug()<<"DataBase is Open";
}
else
{
qDebug()<<"DataBase is Not Open";
}
QSqlQueryModel * model = new QSqlQueryModel();
QSqlQuery query(QSqlDatabase::database("conn_name"));
query.exec("SMTHING")
if (query.exec())
{
while (query.next())
{
ui->QTableView->setModel(model);
model->setHeaderData(2, Qt::Horizontal, QObject::tr("????"));
}
}
db.close();
QSqlDatabase::removeDatabase("conn_name");
Here is my code
I have a simple application, where I can log in / out users. When user logs in, application shows appropriate tab on main window (employee/admin/customer). I have a QMainWindow with QTabWidget on it. In my QMainWindow I create a database (I implemented a special class for this):
class DataBase
{
public:
DataBase();
void initDatabase();
void closeDatabase();
private:
QSqlDatabase db;
};
DataBase::DataBase()
{
}
void DataBase::initDatabase()
{
QString filename = "database.sql";
QFile file(filename);
db = QSqlDatabase::addDatabase("QSQLITE");
db.setHostName("localhost");
db.setDatabaseName(filename);
// create users table
if(this->db.open())
{
QSqlQuery usersTableQuery;
QString usersTableQueryStr = "CREATE TABLE IF NOT EXISTS USERS (ID INTEGER PRIMARY KEY NOT NULL, "
"LOGIN TEXT,"
"PASSWORD TEXT,"
"FIRSTNAME TEXT,"
"LASTNAME TEXT,"
"EMAIL TEXT,"
"ACCOUNT_TYPE INTEGER"
");";
if(usersTableQuery.exec(usersTableQueryStr))
{
qDebug() << "Create USERS table OK";
}
else
{
qDebug() << usersTableQuery.lastError().text();
}
}
else
{
qDebug() << "DB is not opened!\n";
}
// create service table
if(this->db.open())
{
QSqlQuery serviceTableQuery;
QString serviceTableQueryStr = "CREATE TABLE IF NOT EXISTS SERVICE (ID INTEGER PRIMARY KEY NOT NULL, "
"NAME TEXT,"
"PRICE REAL"
");";
if(serviceTableQuery.exec(serviceTableQueryStr))
{
qDebug() << "Create SERVICE table OK";
}
else
{
qDebug() << serviceTableQuery.lastError().text();
}
}
else
{
qDebug() << "DB is not opened!\n";
}
}
void DataBase::closeDatabase()
{
db.close();
}
My tabs for employee, admin, client look like this one:
class AdminTab : public QWidget
{
Q_OBJECT
public:
explicit AdminTab(DataBase *db, QWidget *parent = 0);
//...
Everyone (employee,client,admin) can make changes in database (for instance, admin can insert services, users can check available services, etc). However, when admin adds a service (I make an insert operation on an open database), and logs out, when the client logs in, it can't see the changes made by the admin. When I start application again, and client logs in, it can see new added service.
Adding service looks like this:
bool DataBase::insertService(QString name, double price)
{
if(!db.isOpen())
{
qDebug() << query.lastError();
return false;
}
else
{
QSqlQuery query;
query.prepare("INSERT INTO SERVICE (NAME, PRICE) "
"VALUES (:NAME, :PRICE)");
query.bindValue(":NAME", name);
query.bindValue(":PRICE", price);
if(query.exec())
{
return true;
}
else
{
qDebug() << query.lastError();
}
}
return false;
}
I guess it's the problem that the database is all the time opened, but how can I make the changes to be available just after I insert/remove something in database? I open the database when I create QMainWindow and close it in its destructor.
I thought about opening/closing the database every time I need to use it, but I can't say if it's a good solution.
Even adding :
if(query.exec())
{
query.clear();
db.commit();
return true;
}
Does not help.
Client has: QVector<Service*> availableServices; and QComboBox *servicesComboBox;, checking for all the available services, when client logs in :
void ClientTab::updateAllServices()
{
availableServices.clear();
availableServices = db->selectAllServices();
servicesComboBox->clear();
for(int i=0; i<availableServices.size(); i++)
servicesComboBox->addItem(availableServices[i]->getServiceName(), QVariant::fromValue(availableServices[i]));
servicesComboBox->setCurrentIndex(-1);
}
Service class:
#ifndef SERVICE_H
#define SERVICE_H
#include <QString>
#include <QMetaType>
#include <QVariant>
class Service : public QObject
{
Q_OBJECT
public:
Service(int id, QString name, double price);
Service(){ id = -1; name = ""; price = 0;}
QString getServiceName() const;
void setServiceName(const QString &value);
double getServicePrice() const;
void setServicePrice(double value);
int getId() const;
void setId(int value);
private:
QString name;
double price;
int id;
};
Q_DECLARE_METATYPE(Service*)
#endif // SERVICE_H
And finally, selecting all services from the database (I use this method to populate combobox on ClientTab):
QVector<Service*> DataBase::selectAllServices()
{
QVector<Service*> services;
if(!db.isOpen())
{
return services;
}
else
{
QSqlQuery query;
if(query.exec("SELECT * FROM SERVICE;"))
{
while( query.next() )
{
int id = query.value(0).toInt();
QString name = query.value(1).toString();
double price = query.value(2).toDouble();
Service *s = new Service(id, name, price);
services.push_back(s);
}
}
else
{
qDebug() << "DataBase::selectAllServices " << query.lastError();
}
}
return services;
}
Could you doublecheck that
void ClientTab::updateAllServices()
is called every time as the client logs in (not only at application start)?
SQLite database has autocommit on by default, therefore you don't need to commit anything or use any transaction for this simple thing.
Can you see the new service added in sqlite command line with a select * from service? If so, then adding a service works well, and you need to check when do you call updateAllServices().
If I understand your problem correctly, it's about how to synchronize multiple views of a database. This is indeed a difficult task.
If only one of the views is visible at any given time (like it seems in your case to be with the different tabs), just reload the data from the database and repopulate the tabs. How would you do this? Add a signal contentChanged() to your main window and let all views reload the data when they see it. (Or clear their data and reload when the user switches to the specific tab.)
In case this is too slow or you can see the same content in multiple views at the same time: You should use the models provided by Qt, e.g. QListView + QAbstractListModel instead of QListWidget. If you use those, synchronization is for free, but you should not access your SQL database directly anymore and only change it through the model.
What is the correct way to handle connections for QSqlDatabase?
In my program I am doing it this way:
DatabaseConnector *databaseConnector = 0;
try
{
databaseConnector = new DatabaseConnector();
//Do stuff...
delete databaseConnector;
}
catch(QString e)
{
delete databaseConnector;
QMessageBox::information(this,"Error",e);
}
databaseConnector.h
#ifndef DATABASECONNECTOR_H
#define DATABASECONNECTOR_H
#include <QtSql>
class DatabaseConnector
{
public:
DatabaseConnector();
DatabaseConnector(QString hostname, QString database, QString user, QString password);
~DatabaseConnector();
private:
QSqlDatabase db;
};
#endif // DATABASECONNECTOR_H
databaseconnector.cpp
#include "databaseconnector.h"
#include <QString>
DatabaseConnector::DatabaseConnector()
{
QSettings settings;
db = QSqlDatabase::addDatabase("QIBASE");
db.setHostName(settings.value("db/host").toString());
db.setDatabaseName(settings.value("db/name").toString());
db.setUserName(settings.value("db/user").toString());
db.setPassword(settings.value("db/pass").toString());
if(!db.open())
{
QString databaseConnectionError = db.lastError().text();
throw databaseConnectionError;
}
}
DatabaseConnector::DatabaseConnector(QString hostname, QString database, QString user, QString password)
{
db = QSqlDatabase::addDatabase("QIBASE");
db.setHostName(hostname);
db.setDatabaseName(database);
db.setUserName(user);
db.setPassword(password);
if(!db.open())
{
QString databaseConnectionError = db.lastError().text();
throw databaseConnectionError;
}
}
DatabaseConnector::~DatabaseConnector()
{
db.close();
}
I'm getting error even if I use QSqlDatabase::removeDatabase(db.connectionName());
QSqlDatabasePrivate::addDatabase: duplicate connection name 'qt_sql_default_connection', old connection removed.
Normally you don’t need to open the database connection more than once within your application.
When adding a database, you can name the connection :
QSqlDatabase::addDatabase( "QIBASE", "MyDBConnectionName" );
You can use the name to query for the connection :
if( QSqlDatabase::contains( "MyDBConnectionName" ) )
{
QSqlDatabase db = QSqlDatabase::database( "MyDBConnectionName" );
//Do stuff...
}
else
{
// connection not found, do something
}
Also notice that before calling QSqlDatabase::removeDatabase you should disconnect your database :
db.close();
QSqlDatabase::removeDatabase("MyDBConnectionName");
In order to add a new database, you need to give it a name. If you do not give a unique name, the default database is re-used. This is documented in the class reference.
Try:
db = QSqlDatabase::addDatabase("QIBASE", databaseName);
In main app:
QSqlDatabase db =QSqlDatabase::addDatabase( "QSQLITE");
in second app:
QSqlDatabase db2 =QSqlDatabase::database();
I am trying to implement a database object for my application, but it became a nightmare when I started using multiple connections. Below, you can see my database C++ class code:
// here are the declarations
QString server_addr;
QString username;
QString password;
QString database_name;
QSqlDatabase connection;
QString error;
QString connectionName;
QSqlQuery m_query;
// and here are the definitions
database::database(QString connectionName) {
preferences p; p.read();
QString iConnectionName = (connectionName == "") ? default_connection_name : connectionName;
this->connectionName = iConnectionName;
if (QSqlDatabase::contains(iConnectionName))
this->connection = QSqlDatabase::database(iConnectionName);
else this->connection = QSqlDatabase::addDatabase("QMYSQL", iConnectionName);
this->connection.setHostName(p.database->server_addr);
this->connection.setUserName(p.database->username);
this->connection.setPassword(p.database->password);
this->connection.setDatabaseName(p.database->database_name);
this->connection.setPort(p.database->serverPort);
if (!connection.open())
{
this->error = this->connection.lastError().text();
}
else this->error = "";
}
QSqlQuery database::query(QString query_text) {
this->m_query = QSqlQuery(query_text, this->connection);
this->m_query.exec();
return m_query;
}
database::~database() {
if (!this->m_query.isActive()) QSqlDatabase::removeDatabase(this->connectionName);
qDebug() << "database object destroyed\n";
}
The problem occurs in a another class (that uses the database):
databaseAdaptor::databaseAdaptor() {
this->db = database();
// other construction operations
}
void databaseAdaptor::fetch() {
QSqlQuery q = db.query("SELECT * FROM `activities`");
qDebug() << "Rows count: " << q.numRowsAffected();
}
It worked some versions in the past, but for some reason, now the output from qDebug() is
Rows count: -1 // and it should be 2 for my current version of database.
In the Qt Documentation, it is said that this class' members are thread-safe. Could this be the problem? I mean, could the thread end before the queries finish their execution?
If so, how can I keep the connection open until all the queries finished their execution?
(I know it's much to read, but I am sure that other might have this problem at some point, so please take your time and read it). Thank you!