QsqlDatabase & QsqlQuery managed in a class -Error removeDatabase: connection 'qt_sql_default_connection' is still in use

[Kamigi]

Hello Everyone,

I would like to create a class which can manage my sqlite db.

I've read already almost all topics regarding this error, but i still can't use it well.

• I tried to execute every QSqlQuery class declaration in the same scope than the db manager ( QsqlDatabase object ).
• I tried also to use pointers, local Member, no member of class ( declared each time by a QsqlDatabase::database(connectionName)

Please find a bit of code to do this :
file: query.h

namespace sql {
    /// Query Class : used to manage Database Structures, Queries, and DB Manipulation(create,update,open/close)
    class query : public QObject
    {
        Q_OBJECT
    public:

    explicit query(QObject *parent = nullptr);
    ~query();
[...]
   private:
[...]
        void initDb(QSqlDatabase db);
        bool openDb(QSqlDatabase db);
        void closeDb(QSqlDatabase db);
        bool createDb(QSqlDatabase db);
        bool updateDb(QSqlDatabase db);
   signals:
   };
}

file : query.cpp

using namespace sql;
query::query(QObject *parent) : QObject{parent}
{
   // create db structure from JSON File
    _dbStruct = new skel::database(); // Custom Class to manage db structure
    // Init QSqlDatabase based on _dbStruct information
    QSqlDatabase sqlDb = QSqlDatabase::addDatabase(skel::database::TYPE[_dbStruct->type()]); // skel::database::TYPE[_dbStruct->type()] = "QSQLITE"
    sqlDb.setDatabaseName(_dbStruct->path() + _dbStruct->name()); // set up the sqlite file path & name
    _dbConnectionName = sqlDb.connectionName(); // retrieve connection Name (not in use in this version of implementation)
    qDebug() << "Qsql DB Connection Name : " << _dbConnectionName;
}

query::~query()
{
    QSqlDatabase sqlDb = QSqlDatabase::database(_dbConnectionName);
    this->closeDb(sqlDb);
   QSqlDatabase::removeDatabase(sqlDb.connectionName());
}

bool query::createDb(QsqlDatabase db)
{
      [...]
      QSqlQuery q = QSqlQuery(db);
      [...]
      // Loop on all tables to create it in database
      for(int i=0;i<_dbStruct->tables()->count(); i++) {
           // Execute Query CREATE TABLE (...)
           isCreated = q.exec(_dbStruct->tables()->at(i)->sql());
           if(!isCreated) {
               qDebug() << "query::createDb():[ERROR]Table -> " << q.lastError();
               return isCreated;
          }
               qDebug().noquote().nospace() << _dbStruct->tables()->at(i)->sql();
      }
      [...]
      q.clear();
      q.prepare("INSERT INTO version ( \"database\", \"application\" ) VALUES (  :dbVal, :appVal  )");
      q.bindValue(":dbVal", _dbStruct->version());
      q.bindValue(":appVal", "1");
      // Exec Insert Prepared Query
      if(!(isCreated = q.exec())) {
           qDebug() << "query::createDb():[ERROR] Unable to Insert Version : " << q.lastError();
      }
}

void query::closeDb(QSqlDatabase db)
{
    int count = 0; while(db.isOpen() && count < 3) {
        count++; qDebug() << "query::closeDb():[INFO]Closing Database ! Attempt " << count << " of 3";
        db.close();
    }
return isCreated;
}

file main.cpp

[...]
sql::query *query = new sql::query();
// Delete query object;
delete query; // <--- !!! ERROR happens here !!!
[...]

When executed, i have still this same error ( for all type of implementations described at the beginning of this thread ) ->

query::closeDb():[INFO]Closing Database ! Attempt  1  of 3
QSqlDatabasePrivate::removeDatabase: connection 'qt_sql_default_connection' is still in use, all queries will cease to work.

N.B. : all my code isn't pasted here, but i think ift's enough to understand how i want to proceed, if there is some missing information, ask me i will share it!

EDIT : post updated with all modifications and remarks done in replies

LAST EDIT : SOLVED ! the problem was in the destructor, here is the correction :

query::~query()
{
    this->closeDb(QSqlDatabase::database(_dbConnectionName));
    QSqlDatabase::removeDatabase(_dbConnectionName);
}

Thanks to everyone for their help !

[Christian Ehrlicher]

You have a QSqlQuery lingering around somewhere (not in the code you showed us).

[Kamigi]

mmm ok, then the only thing i do it's to call QSqlQuery instance (q) inside the same method ( query::createDb(QSqlDatabase db)) in a for loop, so maybe the scope isn't clear for QSqlDatabase, cause i called the QsqlQuery in a sub scope, else i don't call it at all :

   QSqlQuery q = QSqlQuery(db);
[...]
   // Loop on all tables to create it in database
   for(int i=0;i<_dbStruct->tables()->count(); i++) {
       // Execute Query CREATE TABLE (...)
       isCreated = q.exec(_dbStruct->tables()->at(i)->sql());
       if(!isCreated) {
           qDebug() << "query::createDb():[ERROR]Table -> " << q.lastError();
           return isCreated;
       }
       qDebug().noquote().nospace() << _dbStruct->tables()->at(i)->sql();
   }
[...]
// Insert Database Current Version
   q.clear();
   q.prepare("INSERT INTO :tbl ( \":dbCol\", \"appCol\" ) VALUES ( \":dbVal\", \":appVal\" )");
   q.bindValue(":tbl", "version");
   q.bindValue(":dbCol", "database");
   q.bindValue(":appCol", "application");
   q.bindValue(":dbVal", "1");
   q.bindValue(":appVal", "1");
   // Exec Insert Prepared Query
   if(!(isCreated = q.exec())) {
       qDebug() << "query::createDb():[ERROR] Unable to Insert Version : " << q.lastError();
   }
   return isCreated;

EDIT : Oh i am really sorry , i forgot to mention the error happens when i try to delete the query pointer :
file:main.cpp

sql::query *query = new sql::query();
// Delete query object;
delete query; // the error shows on this call (it calls query::~query())

file query.cpp

query::~query()
{
    QSqlDatabase sqlDb = QSqlDatabase::database(_dbConnectionName);
    this->closeDb(sqlDb);
    sqlDb.removeDatabase(sqlDb.connectionName());
}

N.B. : i updated first post with all these infos

[hskoglund]

Hi, perhaps your query (the 2nd one) with "INSERT INTO..." is still in an active state, try doing a next() or a finish() at the end, say like this:

// Exec Insert Prepared Query
if(!(isCreated = q.exec())) {
       qDebug() << "query::createDb():[ERROR] Unable to Insert Version : " << q.lastError();
}
q.finish();   // here
return isCreated;

[Christian Ehrlicher]

@Kamigi said in QsqlDatabase & QsqlQuery managed in a class -Error removeDatabase: connection 'qt_sql_default_connection' is still in use:

QSqlDatabase sqlDb = QSqlDatabase::database(_dbConnectionName);
this->closeDb(sqlDb);
sqlDb.removeDatabase(sqlDb.connectionName());

This is wrong. removeDabase is static and therefore needs no instance (which is the one which is tirggering the warning)

[Nevez]

did it work? I do not think so

[Kamigi]

Hi again,

First many thanks for your time !

How could i not see that, i know already all these methods are statics (that is what annoying me in fact :D) ...

so i replace by the static method:

QSqlDatabase sqlDb = QSqlDatabase::database(_dbConnectionName);
this->closeDb(sqlDb);
QSqlDatabase::removeDatabase(sqlDb.connectionName());

i still have the same error, maybe i should use open and close static methods also ? (i don't know if those two are static ones...)
I will check this, many thanks , i think you got me on the good way !

EDIT : according to Qt Documentation ( QSqlDatabase Class ), open and close are not statics, they are public ...

[KroMignon]

@Kamigi said in QsqlDatabase & QsqlQuery managed in a class -Error removeDatabase: connection 'qt_sql_default_connection' is still in use:

so i replace by the static method:

QSqlDatabase sqlDb = QSqlDatabase::database(_dbConnectionName);
this->closeDb(sqlDb);
QSqlDatabase::removeDatabase(sqlDb.connectionName());

The problem here is that an instance of the DB still exists!
Why you do not simply do QSqlDatabase::removeDatabase(_dbConnectionName); ?
Or insure that no QSqlDatabase is in use:

this->closeDb(QSqlDatabase::database(_dbConnectionName));
QSqlDatabase::removeDatabase(_dbConnectionName);

[Kamigi]

You really are the best !!!

many thanks error disappear !

here is the code for the destructor as you suggested :

query::~query()
{
    this->closeDb(QSqlDatabase::database(_dbConnectionName));
    QSqlDatabase::removeDatabase(_dbConnectionName);
}

I guess topic is closed !!! , i update the first post with answer and mark it as solved !!!

Many thanks once again!