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Software development challenges around index creation for data models

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  • kshegunovK kshegunov

    @elfring said in Software development challenges around index creation for data models:

    How would you map a data model to Qt programming interfaces when each level within a hierarchy should correspond to a specific class?

    Explain what you mean by that.

    E Offline
    E Offline
    elfring
    wrote on last edited by
    #15

    Explain what you mean by that.

    Will the following hierarchy example help for a better common understanding of a possible data model?

    1. Directories contain files.
    2. Text files can contain several lines.
    3. Text lines contain characters.

    Which classes would you like to use then in your software application?

    kshegunovK 1 Reply Last reply
    0
    • VRoninV Offline
      VRoninV Offline
      VRonin
      wrote on last edited by
      #16

      I'd use the QVariant approach (so both QStandardItemModel and the one above should work) you can store directories and files as QUrls to the local path and text lines as QString

      "La mort n'est rien, mais vivre vaincu et sans gloire, c'est mourir tous les jours"
      ~Napoleon Bonaparte

      On a crusade to banish setIndexWidget() from the holy land of Qt

      E 1 Reply Last reply
      0
      • E elfring

        Explain what you mean by that.

        Will the following hierarchy example help for a better common understanding of a possible data model?

        1. Directories contain files.
        2. Text files can contain several lines.
        3. Text lines contain characters.

        Which classes would you like to use then in your software application?

        kshegunovK Offline
        kshegunovK Offline
        kshegunov
        Moderators
        wrote on last edited by
        #17

        The model infra is abstract enough so you can attach whatever you want to it. What you're describing is (kind of) a file system model with additional tweaks so you can subclass it and implement the last part. Or you can start from scratch and implement your own if you like.

        For my current project I use the model simply as a proxy to an abstract class that holds the data (due to various reasons), so you can do that either if you like. The options are limitless ...

        Read and abide by the Qt Code of Conduct

        E 1 Reply Last reply
        0
        • VRoninV VRonin

          I'd use the QVariant approach (so both QStandardItemModel and the one above should work) you can store directories and files as QUrls to the local path and text lines as QString

          E Offline
          E Offline
          elfring
          wrote on last edited by
          #18

          I'd use the QVariant approach

          I am occasionaly trying to avoid the data transfer by such a generic class.

          Will it make sense to apply an other software design composition?

          • Can it make sense to map even simple hierarchy levels to separate model classes?
          • Should relationships between model instances be expressed separately?
          1 Reply Last reply
          0
          • kshegunovK kshegunov

            The model infra is abstract enough so you can attach whatever you want to it. What you're describing is (kind of) a file system model with additional tweaks so you can subclass it and implement the last part. Or you can start from scratch and implement your own if you like.

            For my current project I use the model simply as a proxy to an abstract class that holds the data (due to various reasons), so you can do that either if you like. The options are limitless ...

            E Offline
            E Offline
            elfring
            wrote on last edited by
            #19

            What you're describing is (kind of) a file system model

            Did anybody try to represent data as a file system for model variants besides the usage of the class “QFileSystemModel”?

            with additional tweaks so you can subclass it and implement the last part.

            I am trying again to clarify corresponding software development possibilities.

            For my current project I use the model simply as a proxy to an abstract class that holds the data …

            This design approach sounds very promising. How should data accesses be redirected to the existing container object here?

            kshegunovK 1 Reply Last reply
            0
            • E elfring

              What you're describing is (kind of) a file system model

              Did anybody try to represent data as a file system for model variants besides the usage of the class “QFileSystemModel”?

              with additional tweaks so you can subclass it and implement the last part.

              I am trying again to clarify corresponding software development possibilities.

              For my current project I use the model simply as a proxy to an abstract class that holds the data …

              This design approach sounds very promising. How should data accesses be redirected to the existing container object here?

              kshegunovK Offline
              kshegunovK Offline
              kshegunov
              Moderators
              wrote on last edited by kshegunov
              #20

              @elfring said in Software development challenges around index creation for data models:

              This design approach sounds very promising. How should data accesses be redirected to the existing container object here?

              MyModel::MyModel(QObject * parent)
                  : QAbstractTableModel(parent), dataSource(nullptr)
              {
              }
              
              void MyModel::setDataSource(MyDataSource * source)
              {
                  if (dataSource)  {
                      QObject::disconnect(this, nullptr, dataSource, nullptr);
                      QObject::disconnect(dataSource, nullptr, this, nullptr);
                  }
              
                  dataSource = source;
              
                  QObject::connect(dataSource, &MyDataSource::dataChangeStarted, this, &MyModel::beginResetModel);
                  QObject::connect(dataSource, &MyDataSource::dataChangeFinished, this, &MyModel::endResetModel);
              }
              
              QVariant MyModel::headerData(int section, Qt::Orientation orientation, int role) const
              {
                  if (role != Qt::DisplayRole || orientation != Qt::Horizontal || section >= dataSource->columnCount())
                      return QVariant();
              
                  Q_ASSERT(dataSource);
                  return dataSource->columnName(section);
              }
              
              int MyModel::rowCount(const QModelIndex &) const
              {
                  Q_ASSERT(dataSource);
                  return dataSource->rowCount();
              }
              
              int MyModel::columnCount(const QModelIndex &) const
              {
                  Q_ASSERT(dataSource);
                  return dataSource->columnCount();
              }
              
              QVariant MyModel::data(const QModelIndex & index, int role) const
              {
                  Q_ASSERT(dataSource);
              
                  if (!index.isValid() || role != Qt::DisplayRole)
                      return QVariant();
              
                  return dataSource->value(index.row(), index.column());
              }
              

              and of course the corresponding interface:

              
              class MyDataSource : public QObject
              {
                  Q_OBJECT
                  Q_DISABLE_COPY(MyDataSource)
              
              public:
                  MyDataSource(QObject * = nullptr);
              
                  virtual int rowCount() const = 0;
                  virtual int columnCount() const = 0;
                  virtual QString columnName(int) const = 0;
                  virtual QVariant value(int, int) const = 0;
              
                  virtual QString format(const QVariant &, int) const;
              
              signals:
                  void changed();
              
                  void dataChangeStarted();
                  void dataChangeFinished();
              
              protected slots:
                  virtual void reloadData() = 0;
              };
              

              Read and abide by the Qt Code of Conduct

              E VRoninV 2 Replies Last reply
              0
              • kshegunovK kshegunov

                @elfring said in Software development challenges around index creation for data models:

                This design approach sounds very promising. How should data accesses be redirected to the existing container object here?

                MyModel::MyModel(QObject * parent)
                    : QAbstractTableModel(parent), dataSource(nullptr)
                {
                }
                
                void MyModel::setDataSource(MyDataSource * source)
                {
                    if (dataSource)  {
                        QObject::disconnect(this, nullptr, dataSource, nullptr);
                        QObject::disconnect(dataSource, nullptr, this, nullptr);
                    }
                
                    dataSource = source;
                
                    QObject::connect(dataSource, &MyDataSource::dataChangeStarted, this, &MyModel::beginResetModel);
                    QObject::connect(dataSource, &MyDataSource::dataChangeFinished, this, &MyModel::endResetModel);
                }
                
                QVariant MyModel::headerData(int section, Qt::Orientation orientation, int role) const
                {
                    if (role != Qt::DisplayRole || orientation != Qt::Horizontal || section >= dataSource->columnCount())
                        return QVariant();
                
                    Q_ASSERT(dataSource);
                    return dataSource->columnName(section);
                }
                
                int MyModel::rowCount(const QModelIndex &) const
                {
                    Q_ASSERT(dataSource);
                    return dataSource->rowCount();
                }
                
                int MyModel::columnCount(const QModelIndex &) const
                {
                    Q_ASSERT(dataSource);
                    return dataSource->columnCount();
                }
                
                QVariant MyModel::data(const QModelIndex & index, int role) const
                {
                    Q_ASSERT(dataSource);
                
                    if (!index.isValid() || role != Qt::DisplayRole)
                        return QVariant();
                
                    return dataSource->value(index.row(), index.column());
                }
                

                and of course the corresponding interface:

                
                class MyDataSource : public QObject
                {
                    Q_OBJECT
                    Q_DISABLE_COPY(MyDataSource)
                
                public:
                    MyDataSource(QObject * = nullptr);
                
                    virtual int rowCount() const = 0;
                    virtual int columnCount() const = 0;
                    virtual QString columnName(int) const = 0;
                    virtual QVariant value(int, int) const = 0;
                
                    virtual QString format(const QVariant &, int) const;
                
                signals:
                    void changed();
                
                    void dataChangeStarted();
                    void dataChangeFinished();
                
                protected slots:
                    virtual void reloadData() = 0;
                };
                
                E Offline
                E Offline
                elfring
                wrote on last edited by
                #21

                and of course the corresponding interface:

                Will your data source provide homogenous items for this model?

                kshegunovK 1 Reply Last reply
                0
                • E elfring

                  and of course the corresponding interface:

                  Will your data source provide homogenous items for this model?

                  kshegunovK Offline
                  kshegunovK Offline
                  kshegunov
                  Moderators
                  wrote on last edited by kshegunov
                  #22

                  @elfring said in Software development challenges around index creation for data models:

                  Will your data source provide homogenous items for this model?

                  Do you mean the data types? If so, then no, the data types are different for the different columns of the table.

                  Read and abide by the Qt Code of Conduct

                  E 1 Reply Last reply
                  0
                  • kshegunovK kshegunov

                    @elfring said in Software development challenges around index creation for data models:

                    Will your data source provide homogenous items for this model?

                    Do you mean the data types? If so, then no, the data types are different for the different columns of the table.

                    E Offline
                    E Offline
                    elfring
                    wrote on last edited by
                    #23

                    …, the data types are different for the different columns of the table.

                    Will your data source work without hierarchies then?

                    kshegunovK 1 Reply Last reply
                    0
                    • kshegunovK kshegunov

                      @elfring said in Software development challenges around index creation for data models:

                      This design approach sounds very promising. How should data accesses be redirected to the existing container object here?

                      MyModel::MyModel(QObject * parent)
                          : QAbstractTableModel(parent), dataSource(nullptr)
                      {
                      }
                      
                      void MyModel::setDataSource(MyDataSource * source)
                      {
                          if (dataSource)  {
                              QObject::disconnect(this, nullptr, dataSource, nullptr);
                              QObject::disconnect(dataSource, nullptr, this, nullptr);
                          }
                      
                          dataSource = source;
                      
                          QObject::connect(dataSource, &MyDataSource::dataChangeStarted, this, &MyModel::beginResetModel);
                          QObject::connect(dataSource, &MyDataSource::dataChangeFinished, this, &MyModel::endResetModel);
                      }
                      
                      QVariant MyModel::headerData(int section, Qt::Orientation orientation, int role) const
                      {
                          if (role != Qt::DisplayRole || orientation != Qt::Horizontal || section >= dataSource->columnCount())
                              return QVariant();
                      
                          Q_ASSERT(dataSource);
                          return dataSource->columnName(section);
                      }
                      
                      int MyModel::rowCount(const QModelIndex &) const
                      {
                          Q_ASSERT(dataSource);
                          return dataSource->rowCount();
                      }
                      
                      int MyModel::columnCount(const QModelIndex &) const
                      {
                          Q_ASSERT(dataSource);
                          return dataSource->columnCount();
                      }
                      
                      QVariant MyModel::data(const QModelIndex & index, int role) const
                      {
                          Q_ASSERT(dataSource);
                      
                          if (!index.isValid() || role != Qt::DisplayRole)
                              return QVariant();
                      
                          return dataSource->value(index.row(), index.column());
                      }
                      

                      and of course the corresponding interface:

                      
                      class MyDataSource : public QObject
                      {
                          Q_OBJECT
                          Q_DISABLE_COPY(MyDataSource)
                      
                      public:
                          MyDataSource(QObject * = nullptr);
                      
                          virtual int rowCount() const = 0;
                          virtual int columnCount() const = 0;
                          virtual QString columnName(int) const = 0;
                          virtual QVariant value(int, int) const = 0;
                      
                          virtual QString format(const QVariant &, int) const;
                      
                      signals:
                          void changed();
                      
                          void dataChangeStarted();
                          void dataChangeFinished();
                      
                      protected slots:
                          virtual void reloadData() = 0;
                      };
                      
                      VRoninV Offline
                      VRoninV Offline
                      VRonin
                      wrote on last edited by
                      #24

                      @kshegunov said in Software development challenges around index creation for data models:

                      QObject::connect(dataSource, &MyDataSource::dataChangeStarted, this, &MyModel::beginResetModel);
                      QObject::connect(dataSource, &MyDataSource::dataChangeFinished, this, &MyModel::endResetModel);

                      I know you can do better than this mate! I know you have to create and connect a gazillion signals but at least you don't build everything from scratch

                      "La mort n'est rien, mais vivre vaincu et sans gloire, c'est mourir tous les jours"
                      ~Napoleon Bonaparte

                      On a crusade to banish setIndexWidget() from the holy land of Qt

                      kshegunovK 1 Reply Last reply
                      0
                      • VRoninV VRonin

                        @kshegunov said in Software development challenges around index creation for data models:

                        QObject::connect(dataSource, &MyDataSource::dataChangeStarted, this, &MyModel::beginResetModel);
                        QObject::connect(dataSource, &MyDataSource::dataChangeFinished, this, &MyModel::endResetModel);

                        I know you can do better than this mate! I know you have to create and connect a gazillion signals but at least you don't build everything from scratch

                        kshegunovK Offline
                        kshegunovK Offline
                        kshegunov
                        Moderators
                        wrote on last edited by kshegunov
                        #25

                        @VRonin said in Software development challenges around index creation for data models:

                        I know you can do better than this mate! I know you have to create and connect a gazillion signals but at least you don't build everything from scratch

                        Actually I can't in this case. I know you want me to emit the row/columns changed and the ***Inserted/***Deleted signals, but it simply isn't applicable in this particular case.

                        PS.
                        Here the data comes from a long JOIN of tables and I'd rather emit modelReset after I had processed all the peculiarities, than to do a fetch from the database on each displayed cell/row.

                        Read and abide by the Qt Code of Conduct

                        1 Reply Last reply
                        1
                        • E elfring

                          …, the data types are different for the different columns of the table.

                          Will your data source work without hierarchies then?

                          kshegunovK Offline
                          kshegunovK Offline
                          kshegunov
                          Moderators
                          wrote on last edited by
                          #26

                          @elfring said in Software development challenges around index creation for data models:

                          Will your data source work without hierarchies then?

                          I don't follow. This is a table model, there's no hierarchy here.

                          Read and abide by the Qt Code of Conduct

                          1 Reply Last reply
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