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How to connect to the database correctly in QtWebApp

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  • Christian EhrlicherC Online
    Christian EhrlicherC Online
    Christian Ehrlicher
    Lifetime Qt Champion
    wrote on last edited by
    #4

    @Mikeeeeee said in How to connect to the database correctly in QtWebApp:

    What do you mean by unique names?

    RTM: https://doc.qt.io/qt-5/qsqldatabase.html#details

    Qt Online Installer direct download: https://download.qt.io/official_releases/online_installers/
    Visit the Qt Academy at https://academy.qt.io/catalog

    1 Reply Last reply
    1
    • M Offline
      M Offline
      Mikeeeeee
      wrote on last edited by
      #5

      I did this from the very beginning and with this approach the server crashes when 2 different objects are connected to the database in parallel

      1 Reply Last reply
      0
      • SGaistS Offline
        SGaistS Offline
        SGaist
        Lifetime Qt Champion
        wrote on last edited by
        #6

        What exactly did you do ?
        What did the stack trace of the crash tell you ?

        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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        0
        • M Offline
          M Offline
          Mikeeeeee
          wrote on last edited by
          #7

          Each new object of the DataBase class reconnects to the database. This object is created each time in a function

          void RequestHandler::service(HttpRequest& request, HttpResponse& response)
          

          And I get error:

          07.06.2020 15:36:44.134 1 WARNING  0x20d4 QSqlDatabasePrivate::addDatabase: duplicate connection name 'qt_sql_default_connection', old connection removed.
          
          jsulmJ 1 Reply Last reply
          0
          • M Mikeeeeee

            Each new object of the DataBase class reconnects to the database. This object is created each time in a function

            void RequestHandler::service(HttpRequest& request, HttpResponse& response)
            

            And I get error:

            07.06.2020 15:36:44.134 1 WARNING  0x20d4 QSqlDatabasePrivate::addDatabase: duplicate connection name 'qt_sql_default_connection', old connection removed.
            
            jsulmJ Offline
            jsulmJ Offline
            jsulm
            Lifetime Qt Champion
            wrote on last edited by
            #8

            @Mikeeeeee said in How to connect to the database correctly in QtWebApp:

            duplicate connection name 'qt_sql_default_connection'

            It doesn't look like you really read the documentation: you do NOT set database name!
            Also it would be helpful if you would post your code...

            https://forum.qt.io/topic/113070/qt-code-of-conduct

            1 Reply Last reply
            1
            • M Offline
              M Offline
              Mikeeeeee
              wrote on last edited by
              #9

              It is my code fore open database:

              void DataBase::openDB()
              {
                  QTextStream out(stdout);
                  ///*
                  dataBase = QSqlDatabase::addDatabase("QPSQL");
                  dataBase.setDatabaseName("db_game_tamada");
                  dataBase.setUserName("postgres");
                  dataBase.setPassword("1qaz");
                  dataBase.setPort(5433);//*/
                  if (dataBase.open()) {
                      //out<<"db is opened \r\n";
                  }
                  else {
                      //out<<"db not opened \r\n";
                  }
              }
              
              void DataBase::closeDB()
              {
                  dataBase.close();
              }
              

              I tried to use it like this:

              void RequestHandler::service(HttpRequest& request, HttpResponse& response)
              {
                  DataBase db;
                  db.openDB();
              
              1 Reply Last reply
              0
              • SGaistS Offline
                SGaistS Offline
                SGaist
                Lifetime Qt Champion
                wrote on last edited by
                #10

                As we already suggested several times: go read the documentation of addDatabase. You are not setting a connection name, therefore all your DataBase objects are using default connection.

                And as I already have written numerous times: Do not keep a local QSqlDatabase member variable. There's a warning in the documentation about that.

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

                SGaistS 1 Reply Last reply
                1
                • M Offline
                  M Offline
                  Mikeeeeee
                  wrote on last edited by
                  #11

                  How I can set connection name? I try this, but this code not work

                      dataBase = QSqlDatabase::addDatabase("QPSQL", "conectionName");
                      dataBase.setDatabaseName("db_game_tamada");
                      dataBase.setUserName("postgres");
                      dataBase.setPassword("1qaz");
                      dataBase.setPort(5433);//*/
                      if (dataBase.open()) {
                          //out<<"db is opened \r\n";
                      }
                      else {
                          //out<<"db not opened \r\n";
                      }
                  

                  I get error: driver not loaded

                  1 Reply Last reply
                  0
                  • SGaistS Offline
                    SGaistS Offline
                    SGaist
                    Lifetime Qt Champion
                    wrote on last edited by
                    #12

                    You need to use a unique name for each connection.

                    As for the error, there's usually a bit more information than that and if not, then set the QT_DEBUG_PLUGINS environment variable to 1 to get more output.

                    You can do it in the Run part of the Project panel in Qt Creator.

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

                    1 Reply Last reply
                    1
                    • M Offline
                      M Offline
                      Mikeeeeee
                      wrote on last edited by
                      #13

                      But how to set the name of the database connection? My previous version does not work even with 1 connection. Please write a correct example.

                      1 Reply Last reply
                      0
                      • SGaistS Offline
                        SGaistS Offline
                        SGaist
                        Lifetime Qt Champion
                        wrote on last edited by
                        #14

                        You used the way the documentation explains.
                        You have now what seems to be an unrelated error.
                        You were asked to provide additional information.
                        Provide them so we can find what is going on.

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

                        1 Reply Last reply
                        1
                        • M Offline
                          M Offline
                          Mikeeeeee
                          wrote on last edited by
                          #15

                          @SGaist said in How to connect to the database correctly in QtWebApp:

                          QT_DEBUG_PLUGINS

                          I use windows7 and in cmd I write "QT_DEBUG_PLUGINS=1" and get error: QT_DEBUG_PLUGINS is not an internal or external command.
                          How use QT_DEBUG_PLUGINS in windows?

                          JonBJ 1 Reply Last reply
                          0
                          • M Mikeeeeee

                            @SGaist said in How to connect to the database correctly in QtWebApp:

                            QT_DEBUG_PLUGINS

                            I use windows7 and in cmd I write "QT_DEBUG_PLUGINS=1" and get error: QT_DEBUG_PLUGINS is not an internal or external command.
                            How use QT_DEBUG_PLUGINS in windows?

                            JonBJ Offline
                            JonBJ Offline
                            JonB
                            wrote on last edited by JonB
                            #16

                            @Mikeeeeee
                            We have previously told you: under Windows in a Command Prompt you have to write:

                            set QT_DEBUG_PLUGINS=1
                            

                            If you are developer it's a really basic thing, you should take your own time to read how to set an environment variable, it's not a Qt thing.

                            1 Reply Last reply
                            1
                            • M Offline
                              M Offline
                              Mikeeeeee
                              wrote on last edited by
                              #17

                              I get this in server log:

                              08.06.2020 13:53:10.942 0 DEBUG    0x26c0 ServiceHelper: Starting service
                              08.06.2020 13:53:11.042 0 DEBUG    0x26c0 HttpListener: Listening on port 8080
                              08.06.2020 13:53:11.042 1 WARNING  0x26c0 Startup: Service has started
                              08.06.2020 13:53:19.333 0 DEBUG    0x26c0 HttpListener: New connection
                              08.06.2020 13:53:19.333 0 DEBUG    0x26c0 HttpConnectionHandler (0x112c0a0): thread started
                              08.06.2020 13:53:19.333 0 DEBUG    0x26c0 HttpConnectionHandler (0x112c0a0): constructed
                              08.06.2020 13:53:19.333 0 DEBUG    0x2838 HttpConnectionHandler (0x112c0a0): handle new connection
                              08.06.2020 13:53:19.334 0 DEBUG    0x2838 HttpConnectionHandler (0x112c0a0): read input
                              08.06.2020 13:53:19.334 0 DEBUG    0x2838 HttpRequest: read request
                              08.06.2020 13:53:19.334 0 DEBUG    0x2838 HttpRequest: from ::ffff:127.0.0.1: POST /getAllCategory HTTP/1.1
                              08.06.2020 13:53:19.334 0 DEBUG    0x2838 HttpRequest: received header host: 127.0.0.1:8080
                              08.06.2020 13:53:19.334 0 DEBUG    0x2838 HttpRequest: received header content-type: application/json
                              08.06.2020 13:53:19.334 0 DEBUG    0x2838 HttpRequest: received header content-length: 46
                              08.06.2020 13:53:19.334 0 DEBUG    0x2838 HttpRequest: received header connection: Keep-Alive
                              08.06.2020 13:53:19.334 0 DEBUG    0x2838 HttpRequest: received header accept-encoding: gzip, deflate
                              08.06.2020 13:53:19.334 0 DEBUG    0x2838 HttpRequest: received header accept-language: ru-RU,en,*
                              08.06.2020 13:53:19.334 0 DEBUG    0x2838 HttpRequest: received header user-agent: Mozilla/5.0
                              08.06.2020 13:53:19.335 0 DEBUG    0x2838 HttpRequest: headers completed
                              08.06.2020 13:53:19.335 0 DEBUG    0x2838 HttpRequest: expect 46 bytes body
                              08.06.2020 13:53:19.443 0 DEBUG    0x2838 HttpConnectionHandler (0x112c0a0): read input
                              08.06.2020 13:53:19.443 0 DEBUG    0x2838 HttpRequest: receive body
                              08.06.2020 13:53:19.443 0 DEBUG    0x2838 HttpRequest: extract and decode request parameters
                              08.06.2020 13:53:19.443 0 DEBUG    0x2838 HttpRequest: extract cookies
                              08.06.2020 13:53:19.443 0 DEBUG    0x2838 HttpConnectionHandler (0x112c0a0): received request
                              08.06.2020 13:53:19.444 0 DEBUG    0x2838 QFactoryLoader::QFactoryLoader() checking directory path "E:/Programs/Qt/5.15.0/mingw81_64/plugins/sqldrivers" ...
                              08.06.2020 13:53:19.445 0 DEBUG    0x2838 QFactoryLoader::QFactoryLoader() looking at "E:/Programs/Qt/5.15.0/mingw81_64/plugins/sqldrivers/qsqlite.dll"
                              08.06.2020 13:53:19.447 1 WARNING  0x2838 Found metadata in lib E:/Programs/Qt/5.15.0/mingw81_64/plugins/sqldrivers/qsqlite.dll, metadata=
                              {
                                  "IID": "org.qt-project.Qt.QSqlDriverFactoryInterface",
                                  "MetaData": {
                                      "Keys": [
                                          "QSQLITE"
                                      ]
                                  },
                                  "archreq": 0,
                                  "className": "QSQLiteDriverPlugin",
                                  "debug": false,
                                  "version": 331520
                              }
                              
                              
                              08.06.2020 13:53:19.447 0 DEBUG    0x2838 Got keys from plugin meta data ("QSQLITE")
                              08.06.2020 13:53:19.447 0 DEBUG    0x2838 QFactoryLoader::QFactoryLoader() looking at "E:/Programs/Qt/5.15.0/mingw81_64/plugins/sqldrivers/qsqlodbc.dll"
                              08.06.2020 13:53:19.448 1 WARNING  0x2838 Found metadata in lib E:/Programs/Qt/5.15.0/mingw81_64/plugins/sqldrivers/qsqlodbc.dll, metadata=
                              {
                                  "IID": "org.qt-project.Qt.QSqlDriverFactoryInterface",
                                  "MetaData": {
                                      "Keys": [
                                          "QODBC3",
                                          "QODBC"
                                      ]
                                  },
                                  "archreq": 0,
                                  "className": "QODBCDriverPlugin",
                                  "debug": false,
                                  "version": 331520
                              }
                              
                              
                              08.06.2020 13:53:19.448 0 DEBUG    0x2838 Got keys from plugin meta data ("QODBC3", "QODBC")
                              08.06.2020 13:53:19.448 0 DEBUG    0x2838 QFactoryLoader::QFactoryLoader() looking at "E:/Programs/Qt/5.15.0/mingw81_64/plugins/sqldrivers/qsqlpsql.dll"
                              08.06.2020 13:53:19.449 1 WARNING  0x2838 Found metadata in lib E:/Programs/Qt/5.15.0/mingw81_64/plugins/sqldrivers/qsqlpsql.dll, metadata=
                              {
                                  "IID": "org.qt-project.Qt.QSqlDriverFactoryInterface",
                                  "MetaData": {
                                      "Keys": [
                                          "QPSQL7",
                                          "QPSQL"
                                      ]
                                  },
                                  "archreq": 0,
                                  "className": "QPSQLDriverPlugin",
                                  "debug": false,
                                  "version": 331520
                              }
                              
                              
                              08.06.2020 13:53:19.449 0 DEBUG    0x2838 Got keys from plugin meta data ("QPSQL7", "QPSQL")
                              08.06.2020 13:53:19.449 0 DEBUG    0x2838 QFactoryLoader::QFactoryLoader() checking directory path "E:/QTProject/build-HttpSerwerQtWebAppGameTamada-Desktop_Qt_5_15_0_MinGW_64_bit-Debug/debug/sqldrivers" ...
                              08.06.2020 13:53:19.457 0 DEBUG    0x2838 loaded library "E:/Programs/Qt/5.15.0/mingw81_64/plugins/sqldrivers/qsqlpsql.dll"
                              08.06.2020 13:53:19.504 1 WARNING  0x2838 QSqlQuery::prepare: database not open
                              08.06.2020 13:53:19.504 0 DEBUG    0x2838 Conroller: finished request
                              08.06.2020 13:53:19.504 0 DEBUG    0x2838 HttpConnectionHandler (0x112c0a0): finished request
                              
                              JonBJ 1 Reply Last reply
                              0
                              • M Mikeeeeee

                                I get this in server log:

                                08.06.2020 13:53:10.942 0 DEBUG    0x26c0 ServiceHelper: Starting service
                                08.06.2020 13:53:11.042 0 DEBUG    0x26c0 HttpListener: Listening on port 8080
                                08.06.2020 13:53:11.042 1 WARNING  0x26c0 Startup: Service has started
                                08.06.2020 13:53:19.333 0 DEBUG    0x26c0 HttpListener: New connection
                                08.06.2020 13:53:19.333 0 DEBUG    0x26c0 HttpConnectionHandler (0x112c0a0): thread started
                                08.06.2020 13:53:19.333 0 DEBUG    0x26c0 HttpConnectionHandler (0x112c0a0): constructed
                                08.06.2020 13:53:19.333 0 DEBUG    0x2838 HttpConnectionHandler (0x112c0a0): handle new connection
                                08.06.2020 13:53:19.334 0 DEBUG    0x2838 HttpConnectionHandler (0x112c0a0): read input
                                08.06.2020 13:53:19.334 0 DEBUG    0x2838 HttpRequest: read request
                                08.06.2020 13:53:19.334 0 DEBUG    0x2838 HttpRequest: from ::ffff:127.0.0.1: POST /getAllCategory HTTP/1.1
                                08.06.2020 13:53:19.334 0 DEBUG    0x2838 HttpRequest: received header host: 127.0.0.1:8080
                                08.06.2020 13:53:19.334 0 DEBUG    0x2838 HttpRequest: received header content-type: application/json
                                08.06.2020 13:53:19.334 0 DEBUG    0x2838 HttpRequest: received header content-length: 46
                                08.06.2020 13:53:19.334 0 DEBUG    0x2838 HttpRequest: received header connection: Keep-Alive
                                08.06.2020 13:53:19.334 0 DEBUG    0x2838 HttpRequest: received header accept-encoding: gzip, deflate
                                08.06.2020 13:53:19.334 0 DEBUG    0x2838 HttpRequest: received header accept-language: ru-RU,en,*
                                08.06.2020 13:53:19.334 0 DEBUG    0x2838 HttpRequest: received header user-agent: Mozilla/5.0
                                08.06.2020 13:53:19.335 0 DEBUG    0x2838 HttpRequest: headers completed
                                08.06.2020 13:53:19.335 0 DEBUG    0x2838 HttpRequest: expect 46 bytes body
                                08.06.2020 13:53:19.443 0 DEBUG    0x2838 HttpConnectionHandler (0x112c0a0): read input
                                08.06.2020 13:53:19.443 0 DEBUG    0x2838 HttpRequest: receive body
                                08.06.2020 13:53:19.443 0 DEBUG    0x2838 HttpRequest: extract and decode request parameters
                                08.06.2020 13:53:19.443 0 DEBUG    0x2838 HttpRequest: extract cookies
                                08.06.2020 13:53:19.443 0 DEBUG    0x2838 HttpConnectionHandler (0x112c0a0): received request
                                08.06.2020 13:53:19.444 0 DEBUG    0x2838 QFactoryLoader::QFactoryLoader() checking directory path "E:/Programs/Qt/5.15.0/mingw81_64/plugins/sqldrivers" ...
                                08.06.2020 13:53:19.445 0 DEBUG    0x2838 QFactoryLoader::QFactoryLoader() looking at "E:/Programs/Qt/5.15.0/mingw81_64/plugins/sqldrivers/qsqlite.dll"
                                08.06.2020 13:53:19.447 1 WARNING  0x2838 Found metadata in lib E:/Programs/Qt/5.15.0/mingw81_64/plugins/sqldrivers/qsqlite.dll, metadata=
                                {
                                    "IID": "org.qt-project.Qt.QSqlDriverFactoryInterface",
                                    "MetaData": {
                                        "Keys": [
                                            "QSQLITE"
                                        ]
                                    },
                                    "archreq": 0,
                                    "className": "QSQLiteDriverPlugin",
                                    "debug": false,
                                    "version": 331520
                                }
                                
                                
                                08.06.2020 13:53:19.447 0 DEBUG    0x2838 Got keys from plugin meta data ("QSQLITE")
                                08.06.2020 13:53:19.447 0 DEBUG    0x2838 QFactoryLoader::QFactoryLoader() looking at "E:/Programs/Qt/5.15.0/mingw81_64/plugins/sqldrivers/qsqlodbc.dll"
                                08.06.2020 13:53:19.448 1 WARNING  0x2838 Found metadata in lib E:/Programs/Qt/5.15.0/mingw81_64/plugins/sqldrivers/qsqlodbc.dll, metadata=
                                {
                                    "IID": "org.qt-project.Qt.QSqlDriverFactoryInterface",
                                    "MetaData": {
                                        "Keys": [
                                            "QODBC3",
                                            "QODBC"
                                        ]
                                    },
                                    "archreq": 0,
                                    "className": "QODBCDriverPlugin",
                                    "debug": false,
                                    "version": 331520
                                }
                                
                                
                                08.06.2020 13:53:19.448 0 DEBUG    0x2838 Got keys from plugin meta data ("QODBC3", "QODBC")
                                08.06.2020 13:53:19.448 0 DEBUG    0x2838 QFactoryLoader::QFactoryLoader() looking at "E:/Programs/Qt/5.15.0/mingw81_64/plugins/sqldrivers/qsqlpsql.dll"
                                08.06.2020 13:53:19.449 1 WARNING  0x2838 Found metadata in lib E:/Programs/Qt/5.15.0/mingw81_64/plugins/sqldrivers/qsqlpsql.dll, metadata=
                                {
                                    "IID": "org.qt-project.Qt.QSqlDriverFactoryInterface",
                                    "MetaData": {
                                        "Keys": [
                                            "QPSQL7",
                                            "QPSQL"
                                        ]
                                    },
                                    "archreq": 0,
                                    "className": "QPSQLDriverPlugin",
                                    "debug": false,
                                    "version": 331520
                                }
                                
                                
                                08.06.2020 13:53:19.449 0 DEBUG    0x2838 Got keys from plugin meta data ("QPSQL7", "QPSQL")
                                08.06.2020 13:53:19.449 0 DEBUG    0x2838 QFactoryLoader::QFactoryLoader() checking directory path "E:/QTProject/build-HttpSerwerQtWebAppGameTamada-Desktop_Qt_5_15_0_MinGW_64_bit-Debug/debug/sqldrivers" ...
                                08.06.2020 13:53:19.457 0 DEBUG    0x2838 loaded library "E:/Programs/Qt/5.15.0/mingw81_64/plugins/sqldrivers/qsqlpsql.dll"
                                08.06.2020 13:53:19.504 1 WARNING  0x2838 QSqlQuery::prepare: database not open
                                08.06.2020 13:53:19.504 0 DEBUG    0x2838 Conroller: finished request
                                08.06.2020 13:53:19.504 0 DEBUG    0x2838 HttpConnectionHandler (0x112c0a0): finished request
                                
                                JonBJ Offline
                                JonBJ Offline
                                JonB
                                wrote on last edited by
                                #18

                                @Mikeeeeee said in How to connect to the database correctly in QtWebApp:

                                08.06.2020 13:53:19.504 1 WARNING 0x2838 QSqlQuery::prepare: database not open

                                1 Reply Last reply
                                0
                                • M Offline
                                  M Offline
                                  Mikeeeeee
                                  wrote on last edited by Mikeeeeee
                                  #19

                                  Yes, if I set connect name, then database not opened. How I can set correctly connect name?

                                  1 Reply Last reply
                                  0
                                  • SGaistS Offline
                                    SGaistS Offline
                                    SGaist
                                    Lifetime Qt Champion
                                    wrote on last edited by
                                    #20

                                    Rather than doing nothing in your if code that checks whether the database is opened, what about printing the error you get form QSqlDatabase ?

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

                                    1 Reply Last reply
                                    1
                                    • M Offline
                                      M Offline
                                      Mikeeeeee
                                      wrote on last edited by
                                      #21

                                      Sanks, it is work

                                          dataBase = QSqlDatabase::addDatabase("QPSQL", "conectionName");
                                          dataBase.setDatabaseName("db_game_tamada");
                                          dataBase.setUserName("postgres");
                                          dataBase.setPassword("1qaz");
                                          //ResumeDB.setHostName("127.0.0.1");
                                          dataBase.setPort(5433);//*/
                                      

                                      and in query need set database

                                      QSqlQuery query(dataBase);
                                      
                                      1 Reply Last reply
                                      0
                                      • SGaistS SGaist

                                        As we already suggested several times: go read the documentation of addDatabase. You are not setting a connection name, therefore all your DataBase objects are using default connection.

                                        And as I already have written numerous times: Do not keep a local QSqlDatabase member variable. There's a warning in the documentation about that.

                                        SGaistS Offline
                                        SGaistS Offline
                                        SGaist
                                        Lifetime Qt Champion
                                        wrote on last edited by
                                        #22

                                        Repeating myself:

                                        @SGaist said in How to connect to the database correctly in QtWebApp:

                                        You need to use a unique name for each connection.

                                        @SGaist said in How to connect to the database correctly in QtWebApp:

                                        And as I already have written numerous times: Do not keep a local QSqlDatabase member variable. There's a warning in the documentation about that.

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

                                        1 Reply Last reply
                                        0

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