Skip to content
  • Categories
  • Recent
  • Tags
  • Popular
  • Users
  • Groups
  • Search
  • Get Qt Extensions
  • Unsolved
Collapse
Brand Logo
  1. Home
  2. Qt Development
  3. General and Desktop
  4. Software development challenges around index creation for data models
Forum Update on Monday, May 27th 2025

Software development challenges around index creation for data models

Scheduled Pinned Locked Moved Unsolved General and Desktop
data modelssoftware designindex creationalgorithmsintegers
26 Posts 3 Posters 6.3k Views
  • Oldest to Newest
  • Newest to Oldest
  • Most Votes
Reply
  • Reply as topic
Log in to reply
This topic has been deleted. Only users with topic management privileges can see it.
  • VRoninV VRonin

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

    Would you like to offer any known indexing approaches directly?

    struct ModelItem{
    ModelItem* parent = nullptr;
    QList<QList<ModelItem*> > children;
    QMap<int,QVariant> data;
    }
    
    E Offline
    E Offline
    elfring
    wrote on last edited by
    #7

    struct ModelItem{

    You have shown another example for a data structure. Which implementation would you choose for the index computation then with the corresponding customised hierarchical data model?

    VRoninV 1 Reply Last reply
    0
    • VRoninV VRonin

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

      This technical detail can trigger software development considerations for the portable value range of signed integers.

      Yes but not really. Qt only supports platforms where int is 4 bytes of 8 bits

      Smaller components can be combined into the integer data type for the final index usage.

      What do you have in mind?

      I find this API not so obvious for the implementation

      I agree it's not intuitive but once you get accustomed to it it works fine.

      E Offline
      E Offline
      elfring
      wrote on last edited by
      #8

      … but once you get accustomed to it it works fine.

      Have you found any information sources where developers shared more of their experiences with customised (hierarchical) data models?

      1 Reply Last reply
      0
      • E elfring

        struct ModelItem{

        You have shown another example for a data structure. Which implementation would you choose for the index computation then with the corresponding customised hierarchical data model?

        VRoninV Offline
        VRoninV Offline
        VRonin
        wrote on last edited by
        #9

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

        You have shown another example for a data structure.

        No, that is a hierarchical level. Something like the below:

        UNTESTED CODE!

        class GenericModel : public QAbstractItemModel{
            Q_DISABLE_COPY(GenericModel)
            struct ModelItem{
                ModelItem* parent = nullptr;
                QVector<QVector<ModelItem*> > children;
                QMap<int,QVariant> data;
                ModelItem(ModelItem* par)
                    :parent(par)
                {}
                ~ModelItem(){
                    for(auto i=children.begin();i!=children.end();++i){
                        for(auto j=i->begin();j!=i->end();++j)
                            delete *j;
                    }
                }
            };
        public:
            explicit GenericModel(QObject* parent = nullptr)
                : QAbstractItemModel(parent)
                , rootItem(new ModelItem(nullptr))
            {}
            ~GenericModel() { delete rootItem;}
            QModelIndex index(int row, int column, const QModelIndex &parent = QModelIndex()) const override{
                Q_ASSERT(checkIndex(parent));
                if(parent.isValid())
                    return createIndex(row,column,itemForIndex(parent));
                return createIndex(row,column, rootItem);
            }
            QModelIndex parent(const QModelIndex &index) const override{
                Q_ASSERT(checkIndex(index, CheckIndexOption::DoNotUseParent));
                return indexForItem(static_cast<ModelItem*>(index.internalPointer()));
            }
            int rowCount(const QModelIndex &parent = QModelIndex()) const override{
                Q_ASSERT(checkIndex(parent));
                if(!parent.isValid())
                    return rootItem->children.size();
                return itemForIndex(parent)->children.size();
            }
            int columnCount(const QModelIndex &parent = QModelIndex()) const override{
                Q_ASSERT(checkIndex(parent));
                const ModelItem* const item =parent.isValid() ? itemForIndex(parent) : rootItem;
                Q_ASSERT(item);
                if(item->children.isEmpty())
                    return 0;
                return item->children.at(0).size();
            }
            QVariant data(const QModelIndex &index, int role = Qt::DisplayRole) const override{
                Q_ASSERT(checkIndex(index));
                const ModelItem* const item = itemForIndex(index);
                if(!item)
                    return QVariant();
                return item->data.value(role);
            }
            bool setData(const QModelIndex &index, const QVariant &value, int role = Qt::EditRole) override{
                Q_ASSERT(checkIndex(index));
                ModelItem* const item = itemForIndex(index);
                if(!item)
                    return false;
                //inefficient but works
                item->data[role] = value;
                dataChanged(index,index,{role});
                return true;
            }
            bool insertRows(int row, int count, const QModelIndex &parent = QModelIndex()) override{
                if(row<0 || row>rowCount(parent) || count<=0)
                    return false;
                ModelItem* const parItem = parent.isValid() ? itemForIndex(parent) : rootItem;
                const int colCount = columnCount(parent);
                beginInsertRows(parent,row,row+count-1);
                while(count--){
                    QVector<ModelItem*> colVector(colCount);
                    for(int i=0;i<colCount;++i)
                        colVector[i]=new ModelItem(parItem);
                    parItem->children.insert(row, colVector);
                }
                endInsertRows();
                return true;
            }
            bool insertColumns(int column, int count, const QModelIndex &parent = QModelIndex()) override{
                if(column<0 || column>columnCount(parent) || count<=0)
                    return false;
                ModelItem* const parItem = parent.isValid() ? itemForIndex(parent) : rootItem;
                const int rowCnt = rowCount(parent);
                if(rowCnt==0)
                    return false; //can't insert columns if no rows are there
                beginInsertColumns(parent,column,column+count-1);
                while(count--){
                    for(int i=0;i<rowCnt;++i)
                        parItem->children[i].insert(column, new ModelItem(parItem));
                }
                endInsertColumns();
                return true;
            }
        private:
            ModelItem* itemForIndex(const QModelIndex& idx) const {
                if(!checkIndex(idx, CheckIndexOption::IndexIsValid))
                    return nullptr;
                const ModelItem* const parentItem = static_cast<ModelItem*>(idx.internalPointer());
                return parentItem->children.at(idx.row()).at(idx.column());
            }
            QModelIndex indexForItem(const ModelItem* const itm) const {
                ModelItem* const parentItem = itm->parent;
                if(!parentItem)
                    return QModelIndex();
                for(int rowIter = 0, maxRow = parentItem->children.size(); rowIter<maxRow;++rowIter){
                    for(int colIter = 0, maxCol = parentItem->children.at(rowIter).size(); colIter<maxCol;++colIter){
                        if(parentItem->children.at(rowIter).at(colIter) == itm)
                            return createIndex(rowIter,colIter,parentItem);
                    }
                }
                Q_UNREACHABLE();
                return QModelIndex();
            }
            ModelItem* rootItem;
        };
        

        "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
        2
        • VRoninV VRonin

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

          You have shown another example for a data structure.

          No, that is a hierarchical level. Something like the below:

          UNTESTED CODE!

          class GenericModel : public QAbstractItemModel{
              Q_DISABLE_COPY(GenericModel)
              struct ModelItem{
                  ModelItem* parent = nullptr;
                  QVector<QVector<ModelItem*> > children;
                  QMap<int,QVariant> data;
                  ModelItem(ModelItem* par)
                      :parent(par)
                  {}
                  ~ModelItem(){
                      for(auto i=children.begin();i!=children.end();++i){
                          for(auto j=i->begin();j!=i->end();++j)
                              delete *j;
                      }
                  }
              };
          public:
              explicit GenericModel(QObject* parent = nullptr)
                  : QAbstractItemModel(parent)
                  , rootItem(new ModelItem(nullptr))
              {}
              ~GenericModel() { delete rootItem;}
              QModelIndex index(int row, int column, const QModelIndex &parent = QModelIndex()) const override{
                  Q_ASSERT(checkIndex(parent));
                  if(parent.isValid())
                      return createIndex(row,column,itemForIndex(parent));
                  return createIndex(row,column, rootItem);
              }
              QModelIndex parent(const QModelIndex &index) const override{
                  Q_ASSERT(checkIndex(index, CheckIndexOption::DoNotUseParent));
                  return indexForItem(static_cast<ModelItem*>(index.internalPointer()));
              }
              int rowCount(const QModelIndex &parent = QModelIndex()) const override{
                  Q_ASSERT(checkIndex(parent));
                  if(!parent.isValid())
                      return rootItem->children.size();
                  return itemForIndex(parent)->children.size();
              }
              int columnCount(const QModelIndex &parent = QModelIndex()) const override{
                  Q_ASSERT(checkIndex(parent));
                  const ModelItem* const item =parent.isValid() ? itemForIndex(parent) : rootItem;
                  Q_ASSERT(item);
                  if(item->children.isEmpty())
                      return 0;
                  return item->children.at(0).size();
              }
              QVariant data(const QModelIndex &index, int role = Qt::DisplayRole) const override{
                  Q_ASSERT(checkIndex(index));
                  const ModelItem* const item = itemForIndex(index);
                  if(!item)
                      return QVariant();
                  return item->data.value(role);
              }
              bool setData(const QModelIndex &index, const QVariant &value, int role = Qt::EditRole) override{
                  Q_ASSERT(checkIndex(index));
                  ModelItem* const item = itemForIndex(index);
                  if(!item)
                      return false;
                  //inefficient but works
                  item->data[role] = value;
                  dataChanged(index,index,{role});
                  return true;
              }
              bool insertRows(int row, int count, const QModelIndex &parent = QModelIndex()) override{
                  if(row<0 || row>rowCount(parent) || count<=0)
                      return false;
                  ModelItem* const parItem = parent.isValid() ? itemForIndex(parent) : rootItem;
                  const int colCount = columnCount(parent);
                  beginInsertRows(parent,row,row+count-1);
                  while(count--){
                      QVector<ModelItem*> colVector(colCount);
                      for(int i=0;i<colCount;++i)
                          colVector[i]=new ModelItem(parItem);
                      parItem->children.insert(row, colVector);
                  }
                  endInsertRows();
                  return true;
              }
              bool insertColumns(int column, int count, const QModelIndex &parent = QModelIndex()) override{
                  if(column<0 || column>columnCount(parent) || count<=0)
                      return false;
                  ModelItem* const parItem = parent.isValid() ? itemForIndex(parent) : rootItem;
                  const int rowCnt = rowCount(parent);
                  if(rowCnt==0)
                      return false; //can't insert columns if no rows are there
                  beginInsertColumns(parent,column,column+count-1);
                  while(count--){
                      for(int i=0;i<rowCnt;++i)
                          parItem->children[i].insert(column, new ModelItem(parItem));
                  }
                  endInsertColumns();
                  return true;
              }
          private:
              ModelItem* itemForIndex(const QModelIndex& idx) const {
                  if(!checkIndex(idx, CheckIndexOption::IndexIsValid))
                      return nullptr;
                  const ModelItem* const parentItem = static_cast<ModelItem*>(idx.internalPointer());
                  return parentItem->children.at(idx.row()).at(idx.column());
              }
              QModelIndex indexForItem(const ModelItem* const itm) const {
                  ModelItem* const parentItem = itm->parent;
                  if(!parentItem)
                      return QModelIndex();
                  for(int rowIter = 0, maxRow = parentItem->children.size(); rowIter<maxRow;++rowIter){
                      for(int colIter = 0, maxCol = parentItem->children.at(rowIter).size(); colIter<maxCol;++colIter){
                          if(parentItem->children.at(rowIter).at(colIter) == itm)
                              return createIndex(rowIter,colIter,parentItem);
                      }
                  }
                  Q_UNREACHABLE();
                  return QModelIndex();
              }
              ModelItem* rootItem;
          };
          
          E Offline
          E Offline
          elfring
          wrote on last edited by
          #10

          that is a hierarchical level.

          Do you distinguish any levels in the object hierarchy of a data model?

          Something like the below:

          This source code example looks also interesting.

          VRoninV 1 Reply Last reply
          0
          • E elfring

            that is a hierarchical level.

            Do you distinguish any levels in the object hierarchy of a data model?

            Something like the below:

            This source code example looks also interesting.

            VRoninV Offline
            VRoninV Offline
            VRonin
            wrote on last edited by
            #11

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

            Do you distinguish any levels in the object hierarchy of a data model?

            You can if you want. Instead of making ModelItem a struct, use it as an interface and subclass it to create different type of items if you need

            "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
            • VRoninV VRonin

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

              Do you distinguish any levels in the object hierarchy of a data model?

              You can if you want. Instead of making ModelItem a struct, use it as an interface and subclass it to create different type of items if you need

              E Offline
              E Offline
              elfring
              wrote on last edited by
              #12

              You can if you want.

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

              kshegunovK VRoninV 2 Replies Last reply
              0
              • E elfring

                You can if you want.

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

                kshegunovK Offline
                kshegunovK Offline
                kshegunov
                Moderators
                wrote on last edited by
                #13

                @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.

                Read and abide by the Qt Code of Conduct

                E 1 Reply Last reply
                1
                • E elfring

                  You can if you want.

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

                  VRoninV Offline
                  VRoninV Offline
                  VRonin
                  wrote on last edited by VRonin
                  #14

                  In this case I'd use a generic item that supports QVariant and store the class in it as data.
                  An alternative is to have an item with a void* (or a common base class if available) containing the class instance and an int that keeps track of what type that pointer is holding so it can be dynamic_casted when needed

                  "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

                  1 Reply Last reply
                  1
                  • 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
                                          0

                                          • Login

                                          • Login or register to search.
                                          • First post
                                            Last post
                                          0
                                          • Categories
                                          • Recent
                                          • Tags
                                          • Popular
                                          • Users
                                          • Groups
                                          • Search
                                          • Get Qt Extensions
                                          • Unsolved