Open MYSQL Database with connectionName

helenebro · wrote on 26 Aug 2015, 09:55

Hi,
I have an application thats needs to connect to two several database.
I can connect this two database but I have the "warning" :

QSqlDatabasePrivate::removeDatabase: connection 'qt_sql_default_connection' is still in use, all queries will cease to work.
QSqlDatabasePrivate::addDatabase: duplicate connection name 'qt_sql_default_connection', old connection removed.

To solve the problem, I have seen I have to add different connection name to my two connection. But when I add connection name, connection to database doesn't work.

  void MyData::getData()
  {
  if(openDataBase()){
      QSqlQuery query;
      QString myquery="SELECT * FROM MaTable";
      if(queryTitre.exec(myquery))
      {
	  ...
      }
      else{
	  qDebug() << queryTitre.lastError().text()<dbData.lastError().text();
      }
      dbData.close();
  }
  }

  bool MyData::openDataBase()
  {
    // dbData = QSqlDatabase::addDatabase("QMYSQL3");			//work but warning
      dbData = QSqlDatabase::addDatabase("QMYSQL3", "myDbName");	//Error
      dbData.setHostName("localhost");
      dbData.setDatabaseName("myDbName");
      dbData.setUserName("myUserName");
      dbData.setPassword("myPassword");
  if(!dbData.open())
  {
      qDebug() <<dbData.lastError().text();
      return false;
  }
  qDebug()<<"database open";
  return true;
  }

With the connectionName, I have the Debug :

database open
"Driver not loaded Driver not loaded" " "

I use Qt 5.2.1 under Ubuntu 14.04

Thank you for your help.

SGaist · wrote on 26 Aug 2015, 21:24

Hi,

You don't need to re-create the database object each time, just create once e.g. in the constructor and open/close the connection as needed.

helenebro · wrote on 27 Aug 2015, 08:49

Thank you for your help.
In reality, I open two differents database from two classes. The first class create the second class.
First class, MyApp:

MyApp::MyApp() {
    MyClass *myClass = new MyClass();
    getDataApp();
}
void MyApp::getDataApp() {
    if(openDataBaseApp()) {
       ...
       dbApp.close();
   }
}
bool MyApp::openDataBaseApp() {
  if(!dbApp.isValid()) {
    dbApp = QSqlDatabase::addDatabase("QMYSQL3");
    dbApp.setHostName("localhost");
    dbApp.setUserName("myUserName");
    dbApp.setPassword("myPassword");
    dbApp.setDatabaseName("databaseMyApp");
  }
  if(!dbApp.open())
  {
    qDebug() << dbApp.lastError().text() << "\n";
    return false;
  }
  return true;
}

Second Class , MyClass:

MyClass::MyClass() {
    getDataMyClass();
}
void MyClass::getDataMyClass() {
    if(openDataBaseMyClass()) {
       ...
      dbMyClass.close()
   }
}
bool MyClass::openDataBaseMyClass() {
  if(!dbMyClass.isValid()) {
    dbMyClass = QSqlDatabase::addDatabase("QMYSQL3");
    dbMyClass.setHostName("localhost");
    dbMyClass.setUserName("myUserName");
    dbMyClass.setPassword("myPassword");
    dbMyClass.setDatabaseName("databaseMyClass");
  }
  if(!dbMyClass.open())
  {
    qDebug() << MyClass.lastError().text() << "\n";
    return false;
  }
  return true;
}

If I put dbMyClass and dbMyApp on respective constructor, I have a problem when I re-call getDataBase, it seems driver not loaded.

MyApp::MyApp() {
    MyClass *myClass = new MyClass();
    dbApp = QSqlDatabase::addDatabase("QMYSQL3");
    dbApp.setHostName("localhost");
    dbApp.setUserName("myUserName");
    dbApp.setPassword("myPassword");
    dbApp.setDatabaseName("databaseMyApp");
    getDataApp();
}
MyClass::MyClass() {
    dbMyClass = QSqlDatabase::addDatabase("QMYSQL3");
    dbMyClass.setHostName("localhost");
    dbMyClass.setUserName("myUserName");
    dbMyClass.setPassword("myPassword");
    dbMyClass.setDatabaseName("databaseMyClass");
    getDataMyClass();
}

This is the log :

dbDataCube is create QSqlDatabase(driver=""QMYSQL3"", database=""databaseMyClass"", host=""localhost"", port=-1, user=""myUserName"", open=false) 
openDataBase dbMyClass
dbMyClass is open 
dbMyClass close
QSqlDatabasePrivate::removeDatabase: connection 'qt_sql_default_connection' is still in use, all queries will cease to work.
QSqlDatabasePrivate::addDatabase: duplicate connection name 'qt_sql_default_connection', old connection removed.
dbApp is create QSqlDatabase(driver=""QMYSQL3"", database=""databaseMyApp"", host=""localhost"", port=-1, user=""myUserName"", open=false) 
dbApp is open 
openDataBase dbMyClass
"Driver not loaded Driver not loaded" false 
dbMyClass not open

SGaist · wrote on 27 Aug 2015, 20:45

Ok, that's because you're not naming your connections when setting up your QSqlDatabase objects. You should give each a different name.

By the way, which OS are you running ?

helenebro · wrote on 28 Aug 2015, 08:19

have to admit I'm a little bit confused.

When I has a connection name, my database doesn't open.
If I setup my QSqlDatabase on constructor (whitout connection name), it works the first timer (with the warning) but if I call again my function to get my database, I have the errror : Driver not loaded

If I understand, I should first create two QSqlDatabase with two different name, then get the QSqlDatabase but in this case I can't open database (access denied).

#include "myapp.h"

MyApp::MyApp(QQmlContext *ctx, QObject *parent) : QObject( parent)
{
        QSqlDatabase::addDatabase("QMYSQL3", "myapp");
        QSqlDatabase::addDatabase("QMYSQL3", "myclass");

        MyClass *myClass = new MyClass();
        ctx->setContextProperty("myClass", myClass);

        dbMyApp = QSqlDatabase::database("myapp");
        dbMyApp.setHostName("localhost");
        dbMyApp.setUserName("userName");
        dbMyApp.setPassword("password");
        dbMyApp.setDatabaseName("dbMyApp");
        getDataMyApp();
}

void MyApp::getDataMyApp()
{
    if(openDataBaseMyApp()) {
         QSqlQuery query ;
         int nb = 0;
         if(query.exec("SELECT * from MaTable"))
         {
             while(query.next()) {
             nb++;
         }
     }
     dbMyApp.close();
     qDebug()<<"there are "<<nb<<"input";
    }
}

bool MyApp::openDataBaseMyApp()
{
    if(!dbMyApp.open())
    {
        qDebug() << dbMyApp.lastError().text() << "\n";
        return false;
    }
    return true;
}


#include "myclass.h"

MyClass::MyClass(QObject *parent) : QObject(parent)
{
    dbMyClass = QSqlDatabase::database("myclass");
    dbMyClass.setHostName("localhost");
    dbMyClass.setUserName("userName");
    dbMyClass.setPassword("password");
    dbMyClass.setDatabaseName("dbMyClass");

    getDataMyClass();
}

void MyClass::getDataMyClass()
{
    if(openDataBaseMyClass()) {
        QSqlQuery query ;
        int nb = 0;
        if(query.exec("SELECT * from MaTable"))
        {
            while(query.next()) {
                nb++;
            }
        }
        dbMyClass.close();
        qDebug()<<"there are "<<nb<<"input";
    }
}

bool MyClass::openDataBaseMyClass()
{
        if(!dbMyClass.open())
        {
            qDebug() << dbMyClass.lastError().text() << "\n";
            return false;
        }
    return true;
}

But I have ther error ;

QSqlDatabasePrivate::database: unable to open database: "Access denied for user 'otherName'@'localhost' (using password: NO) QMYSQL: Impossible d'établir une connexion" 
QSqlQuery::exec: database not open
il y a  0 product dans la base 
QSqlDatabasePrivate::database: unable to open database: "Access denied for user 'otherName'@'localhost' (using password: NO) QMYSQL: Impossible d'établir une connexion" 
QSqlQuery::exec: database not open
il y a  0 titre dans la base

SGaist · wrote on 28 Aug 2015, 22:18

That's not a Qt problem there. You otherName user doesn't have access to the database you want to get.

helenebro · wrote on 31 Aug 2015, 07:18

Yes but "OtherName" isn't the name that I have set with dbMyApp.setUserName("userName");

SGaist · wrote on 31 Aug 2015, 21:26

How did you setup the databases ?

Out of curiosity, why two different databases for your application ?

helenebro · wrote on 1 Sept 2015, 10:18

What do you mean by saying "setup" ?

MyApp

MyApp::MyApp(QQmlContext *ctx, QObject *parent) : QObject( parent)
{
    QSqlDatabase::addDatabase("QMYSQL3", "myapp");
    QSqlDatabase::addDatabase("QMYSQL3", "myclass");
    MyClass *myClass = new MyClass();
    ctx->setContextProperty("myClass", myClass);
    dbMyApp = QSqlDatabase::database("myapp");
    dbMyApp.setHostName("localhost");
    dbMyApp.setUserName("root");
    dbMyApp.setPassword("mySQL:r00t");
    dbMyApp.setDatabaseName("cube_application");
    getDataMyApp();
}

MyClass

MyClass::MyClass(QObject *parent) : QObject(parent)
{
    dbMyClass = QSqlDatabase::database("myclass");
    dbMyClass.setHostName("localhost");
    dbMyClass.setUserName("root");
    dbMyClass.setPassword("mySQL:r00t");
    dbMyClass.setDatabaseName("catalogue_4mod");
    getDataMyClass();
}

I have two databases because data have no relationship. My application contains several "mini application".

SGaist · wrote on 1 Sept 2015, 10:23

I meant server side setup.

But again why multiple databases ? You can have your unrelated tables in only one database. They don't need to have any relation between them.

helenebro · wrote on 1 Sept 2015, 10:29

My database is only on localhost and create by command line.
Indeed the two database can be merged, I find it more clear like this (It is maybe a mistake)

SGaist · wrote on 1 Sept 2015, 13:08

Do you mean you find it more clear to connect your application to two different databases ?

helenebro · wrote on 1 Sept 2015, 13:25

Yes, because my application is the merge of different application which has a data on database

SGaist · wrote on 1 Sept 2015, 21:03

That I understood, but still, deploying several databases for one application sounds like an overkill.

helenebro · 9 Feb 2015, 08:42

Ok, I will merge my two databases

lqsa · wrote on 23 Nov 2017, 12:19

In my app, the error

QSqlDatabasePrivate::removeDatabase: connection 'qt_sql_default_connection' is still in use, all queries will cease to work.
QSqlDatabasePrivate::addDatabase: duplicate connection name 'qt_sql_default_connection', old connection removed.

solves when pass the database on QSqlQuery constructor.

In your case could be something like QSqlQuery(dbMyClass) for querys on MyClass and QSqlQuery(dbApp) for querys on MyApp.