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[SOLVED] Problem with QSqlDatabase

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  • S Offline
    S Offline
    stoyanps
    wrote on last edited by
    #2

    About 3 times messages, I guess it is because somewhere in your program you call function getUser() at least three times. First time connection is created and every next time it is removed and created again.

    The error "QSqlError(-1, "Error opening database", "out of memory")" can be caused by location of your database. In Windows 7 for folders under "Users" there are limited access rights. It is possible that your program have no right to create and/or modify database on this location. I suggest to change location of database to "C:\Test\userDatabase.db.sqlite" for example or some other folder.

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    • J Offline
      J Offline
      joonne
      wrote on last edited by
      #3

      That is the weird part because I am pretty sure that I call the getUser() function only 1 time but I don't know why the output looks like that. I changed the location of database as you suggested but the error message is still the same.

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      • SGaistS Offline
        SGaistS Offline
        SGaist
        Lifetime Qt Champion
        wrote on last edited by
        #4

        Hi and welcome to devnet,

        First thing you should do is open your database connection only once at the start of your program since you are using SQLite. Then, if getUser is a slot, verify that you don't connect to it several times.

        Hope it helps

        Interested in AI ? www.idiap.ch
        Please read the Qt Code of Conduct - https://forum.qt.io/topic/113070/qt-code-of-conduct

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        • P Offline
          P Offline
          panosk
          wrote on last edited by
          #5

          Line 12 should be
          @
          if(db_.open()) { //lowercase "o"
          @

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          • J Offline
            J Offline
            joonne
            wrote on last edited by
            #6

            So it would be a good way to make separate functions for example openDB() and something like that? Thanks I will give it a try.

            Thanks to panoski also for pointing the mistake, I forgot it because I modified the code a bit.

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            • J Offline
              J Offline
              joonne
              wrote on last edited by
              #7

              I made separate function for opening the database and I call it at the begin of my program and it solved other problems except the one that matters the most so it doesn't open the database. The error messages in the output are: @QSqlError(-1, "Error opening database", "out of memory")
              Unable to open input file: No such file or directory@

              Is there something wrong with my path or what could cause this?

              I am now using this code to open the database:

              @bool User::openDB() {

              // Find QSLite driver
              db_ = QSqlDatabase::addDatabase("QSQLITE");
              db_.setDatabaseName("C:/Databases/userDatabase.db.sqlite");
              
              // Open databasee
              if(db_.open()) {
                  return true;
              } else {
                  qDebug() << db_.lastError();
                  return false;
              }
              

              }@

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              • SGaistS Offline
                SGaistS Offline
                SGaist
                Lifetime Qt Champion
                wrote on last edited by
                #8

                How big is your database ?

                Interested in AI ? www.idiap.ch
                Please read the Qt Code of Conduct - https://forum.qt.io/topic/113070/qt-code-of-conduct

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                • J Offline
                  J Offline
                  joonne
                  wrote on last edited by
                  #9

                  The database is 2kB and contains only 1 row of User's information such as name and age.

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                  • P Offline
                    P Offline
                    panosk
                    wrote on last edited by
                    #10

                    And how did you modify the User::getUser() function?

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                    • J Offline
                      J Offline
                      joonne
                      wrote on last edited by
                      #11

                      The function is now like this:

                      @bool User::getUser() {

                      bool ret = false;
                      
                      if(db_.isOpen()) {
                      
                          QSqlQuery query("SELECT * FROM user;",db_);
                          qDebug() << query.lastError();
                      
                          if (query.first()) {
                      
                              name_ = query.value(1).toString();
                              age_ = query.value(2).toInt();
                              gender_ = query.value(3).toString();
                              height_ = query.value(4).toDouble();
                              weight_ = query.value(5).toDouble();
                              ret = true;
                          }
                      }
                      
                      return ret;
                      

                      }@

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                      • J Offline
                        J Offline
                        joonne
                        wrote on last edited by
                        #12

                        And I think I should have specified before but I am making a Sailfish application here, does that affect to your advice a lot? Sorry if this was a vital information :/

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                        • P Offline
                          P Offline
                          panosk
                          wrote on last edited by
                          #13

                          I remember a post where a user had trouble with this QSqlQuery constructor. Try to change your function like this:
                          @
                          bool User::getUser() {

                          bool ret = false;
                          
                          if(db_.isOpen()) {
                          
                              QSqlQuery query(db_);
                              if(!query.exec&#40;"SELECT * FROM user"&#41;)
                                  qDebug() << query.lastError();
                          
                              if (query.first()) {
                          
                                  name_ = query.value(1).toString();
                                  age_ = query.value(2).toInt();
                                  gender_ = query.value(3).toString();
                                  height_ = query.value(4).toDouble();
                                  weight_ = query.value(5).toDouble();
                                  ret = true;
                              }
                          }
                          
                          return ret;
                          

                          }
                          @

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                          • J Offline
                            J Offline
                            joonne
                            wrote on last edited by
                            #14

                            I changed the function like you said but the database isn't open so I cant test this but it looks better, thanks.

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                            • P Offline
                              P Offline
                              panosk
                              wrote on last edited by
                              #15

                              Of course, the error prints when opening the database.... Anyway, I suppose you have also double-checked that the path and database file name are accurate.

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                              • SGaistS Offline
                                SGaistS Offline
                                SGaist
                                Lifetime Qt Champion
                                wrote on last edited by
                                #16

                                Indeed you should have mention that earlier. Are you running this application on your Windows computer or on the Sailfish emulator/device ? In the second case I don't think it will access your hard drive to get the file hence the error "no such file or directory"

                                Interested in AI ? www.idiap.ch
                                Please read the Qt Code of Conduct - https://forum.qt.io/topic/113070/qt-code-of-conduct

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                                • S Offline
                                  S Offline
                                  stoyanps
                                  wrote on last edited by
                                  #17

                                  First in function OpenDB add this:
                                  @ if(db_.open()) {
                                  QStringList tables = db_.tables();
                                  qDebug() << "Tables: " << tables;
                                  return true;
                                  } else {@

                                  This will show you all tables in your database if connection is successful.

                                  1. In the beginning of function getUser add this:
                                    @QSqlDatabase db_ = QSqlDatabase::database();
                                    if(db_.isOpen()) {
                                    QSqlQuery query(db_);@
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                                  • J Offline
                                    J Offline
                                    joonne
                                    wrote on last edited by
                                    #18

                                    Thanks for replies. I am running the application in Sailfish emulator and I think I should now get familiar with the usage of local storage and how to get database available for my Sailfish application. After that I can continue with these comments you have given.

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                                    • J Offline
                                      J Offline
                                      joonne
                                      wrote on last edited by
                                      #19

                                      I am a bit confused now. Does someone know how I could store my existing database to local storage and how I could refer to it and use it from my c++ class/object? I did found some examples on how to access database from QML but I would like to access my database from the c++ backend.

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                                      • p3c0P Offline
                                        p3c0P Offline
                                        p3c0
                                        Moderators
                                        wrote on last edited by
                                        #20

                                        Hi,

                                        This test code might help you

                                        @
                                        MainWindow::MainWindow(QWidget *parent) :
                                        QMainWindow(parent),
                                        ui(new Ui::MainWindow)
                                        {
                                        ui->setupUi(this);

                                        if(ConnectLocalDB())
                                            GetData();
                                        

                                        }

                                        MainWindow::~MainWindow()
                                        {
                                        delete ui;
                                        }

                                        bool MainWindow::ConnectLocalDB()
                                        {
                                        db = QSqlDatabase::addDatabase("QSQLITE");

                                        QString dbpath = "/root/testd.db";
                                        db.setDatabaseName(dbpath);
                                        
                                        QSqlQuery query(QSqlDatabase::database());
                                        query.exec&#40;"CREATE TABLE testtable ("
                                                   "id  INTEGER PRIMARY KEY AUTOINCREMENT NOT NULL,"
                                                   "testcolumn TEXT&#41;;"
                                                   );
                                        
                                        query.exec&#40;"insert into testtable(testcolumn&#41; values('one')");
                                        query.exec&#40;"insert into testtable(testcolumn&#41; values('two')");
                                        query.exec&#40;"insert into testtable(testcolumn&#41; values('three')");
                                        
                                        qDebug() << dbpath;
                                        
                                        return db.open();
                                        

                                        }

                                        bool MainWindow::GetData()
                                        {
                                        QSqlQuery query(QSqlDatabase::database());
                                        QString q = "select * from testtable;";
                                        query.exec(q);
                                        while(query.next())
                                        {
                                        qDebug() << query.value(1).toString();
                                        }
                                        }
                                        @

                                        157

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                                        • J Offline
                                          J Offline
                                          joonne
                                          wrote on last edited by
                                          #21

                                          Thanks. I tried with that test code, but I get these errors when I try to open the test database to /root/test.db:

                                          @QSqlDatabasePrivate::database: unable to open database: "out of memory Error opening database"
                                          QSqlQuery::exec: database not open
                                          QSqlQuery::exec: database not open
                                          QSqlQuery::exec: database not open
                                          QSqlQuery::exec: database not open
                                          "/root/testd.db"@

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