QML and QSqlTableModel: Difference between revisions

From Qt Wiki
Jump to navigation Jump to search
(Decode HTML entity names)
No edit summary
Line 21: Line 21:
  QLSqlTableModel(QObject *parent = 0);
  QLSqlTableModel(QObject *parent = 0);
  ~QLSqlTableModel();
  ~QLSqlTableModel();
public:
  Q_INVOKABLE QVariant data(const QModelIndex &index, int role=Qt::DisplayRole ) const;
  Q_INVOKABLE QVariant data(const QModelIndex &index, int role=Qt::DisplayRole ) const;
  void generateRoleNames();
  void generateRoleNames();
#ifdef HAVE_QT5
#ifdef HAVE_QT5
  virtual QHash<int, QByteArray> roleNames() const{return roles;}
  virtual QHash<int, QByteArray> roleNames() const{return roles;}
Line 30: Line 33:
QVariant QLSqlTableModel::data ( const QModelIndex & index, int role ) const
QVariant QLSqlTableModel::data ( const QModelIndex & index, int role ) const
{
{
if(index.row() >= rowCount())
  if(index.row() >= rowCount())
return QString("");
  {
}
      return QString("");
if(role < Qt::UserRole)
  }
{
 
return QSqlQueryModel::data(index, role);
  if(role < Qt::UserRole)
}
  {
else {
      return QSqlQueryModel::data(index, role);
// search for relationships
  }  
for (int i = 0; i < columnCount(); i+'') {
  else  
if (this->relation(i).isValid()) {
  {
return record(index.row()).value(QString(roles.value(role)));
    // search for relationships
}
    for (int i = 0; i < columnCount(); i+'')  
}
    {
// if no valid relationship was found
        if (this->relation(i).isValid())  
return QSqlQueryModel::data(this->index(index.row(), role - Qt::UserRole - 1), Qt::DisplayRole);
        {
}
            return record(index.row()).value(QString(roles.value(role)));
        }
    }
 
    // if no valid relationship was found
    return QSqlQueryModel::data(this->index(index.row(), role - Qt::UserRole - 1), Qt::DisplayRole);
  }
}


</code>
</code>
Line 55: Line 65:
void QLSqlTableModel::generateRoleNames()
void QLSqlTableModel::generateRoleNames()
{
{
roles.clear();
  roles.clear();
int nbCols = this->columnCount();
 
for (int i = 0; i < nbCols; i) {
  int nbCols = this->columnCount();
roles[Qt::UserRole'' i + 1] = QVariant(this->headerData(i, Qt::Horizontal).toString()).toByteArray();
 
  for (int i = 0; i < nbCols; i)  
  {
      roles[Qt::UserRole'' i + 1] = QVariant(this->headerData(i, Qt::Horizontal).toString()).toByteArray();
  }


}
#ifndef HAVE_QT5
#ifndef HAVE_QT5
  setRoleNames(roles);
  setRoleNames(roles);

Revision as of 10:36, 12 April 2015

This article may require cleanup to meet the Qt Wiki's quality standards. Reason: Auto-imported from ExpressionEngine.
Please improve this article if you can. Remove the {{cleanup}} tag and add this page to Updated pages list after it's clean.

QML and QSqlTableModel

I wrote a simple class derived from QSqlRelationalTableModel to facilitate the use of such classes with QML, without manually defining the roles.

If you want to understand why roles are so important when working with SQL table models and QML, have a look at this explained code snippet

class QLSqlTableModel : public QSqlRelationalTableModel
{
 Q_OBJECT
private:
 QHash<int, QByteArray> roles;

public:
 QLSqlTableModel(QObject *parent = 0);
 ~QLSqlTableModel();

public:
 Q_INVOKABLE QVariant data(const QModelIndex &index, int role=Qt::DisplayRole ) const;
 void generateRoleNames();

#ifdef HAVE_QT5
 virtual QHash<int, QByteArray> roleNames() const{return roles;}
#endif
}

QVariant QLSqlTableModel::data ( const QModelIndex & index, int role ) const
{
   if(index.row() >= rowCount())
   {
       return QString("");
   }

   if(role < Qt::UserRole)
   {
       return QSqlQueryModel::data(index, role);
   } 
   else 
   {
     // search for relationships
     for (int i = 0; i < columnCount(); i+'') 
     {
         if (this->relation(i).isValid()) 
         {
            return record(index.row()).value(QString(roles.value(role)));
         }
     }

     // if no valid relationship was found
     return QSqlQueryModel::data(this->index(index.row(), role - Qt::UserRole - 1), Qt::DisplayRole);
   }
}

The data method returns the value of the role used. If there is a relationship in the table, i search the column with relation and return the correct value.. Note that empty string is returned when the item is not found and not QVariant value, in order to have a correct visualization in QML.

void QLSqlTableModel::generateRoleNames()
{
  roles.clear();

  int nbCols = this->columnCount();

  for (int i = 0; i < nbCols; i) 
  {
      roles[Qt::UserRole'' i + 1] = QVariant(this->headerData(i, Qt::Horizontal).toString()).toByteArray();
  }

#ifndef HAVE_QT5
 setRoleNames(roles);
#endif
}

The generateRoleNames method creates the roles called as the table columns specified in the header.

Example:

Tables:

query.exec("create table IF NOT EXISTS items (id integer primary key autoincrement,
name varchar(15), descr varchar(30))");
 query.exec("create table IF NOT EXISTS lista (id integer primary key autoincrement,
qta varchar(30), item INTEGER, FOREIGN KEY (item) REFERENCES items(id))");

main.cpp

QLSqlTableModel *model = new QLSqlTableModel;
 QLSqlTableModel *modelLista = new QLSqlTableModel;
 model->setTable("items");
 model->generateRoleNames();
 model->select();
 modelList->setTable("lists");
 modelList->setRelation(2, QSqlRelation("items", "id", "name"));
 modelList->select();
 modelList->generateRoleNames();
 QDeclarativeContext *ctxt = view.rootContext();
 ctxt->setContextProperty("modelListItems", model);
 ctxt->setContextProperty("modelList", modelLista);

In qml file

Text {
 id: name
 text: model.name
 font.bold: true; font.pointSize: 16
 color: "white"
 }
 Text {
 text: "Amount: " + model.qta
 font.pointSize: 16
 opacity: 1
 color: "white"
 }



Note1: Nice post, however the performance can be tweaked. data() will be called very often. Most of the processing and object instantiation should be done only once.

Note2: I modified provided code according to this working example which was based on this wiki page