Only show writable fields in field calculator

Fix #15000

python/gui/qgsfieldmodel.sip

@@ -46,6 +46,15 @@ class QgsFieldModel : QAbstractItemModel
 
     //! returns the currently used layer
     QgsVectorLayer* layer();
+    /**
+     * The currently applied filters that define which fields are shown.
+     */
+    Filters filters() const;
+
+    /**
+     * The currently applied filters that define which fields are shown.
+     */
+    void setFilters( const Filters& filter );
 
   public slots:
     //! set the layer of whch fields are displayed

src/app/qgsattributetabledialog.cpp

@@ -248,6 +248,7 @@ QgsAttributeTableDialog::QgsAttributeTableDialog( QgsVectorLayer *theLayer, QWid
   mUpdateExpressionText->registerGetExpressionContextCallback( &_getExpressionContext, mLayer );
 
   mFieldModel = new QgsFieldModel( this );
+  mFieldModel->setFilters( QgsFieldModel::WritableFields );
   mFieldModel->setLayer( mLayer );
   mFieldCombo->setModel( mFieldModel );
   connect( mRunFieldCalc, SIGNAL( clicked() ), this, SLOT( updateFieldFromExpression() ) );

src/app/qgsfieldcalculator.cpp

@@ -435,12 +435,14 @@ void QgsFieldCalculator::populateFields()
   const QgsFields& fields = mVectorLayer->fields();
   for ( int idx = 0; idx < fields.count(); ++idx )
   {
+    if ( fields.fieldOrigin( idx ) != QgsFields::OriginExpression && fields.fieldOrigin( idx ) != QgsFields::OriginJoin )
+    {
+      QString fieldName = fields.at( idx ).name();
 
-    QString fieldName = fields[idx].name();
-
-    //insert into field list and field combo box
-    mFieldMap.insert( fieldName, idx );
-    mExistingFieldComboBox->addItem( fieldName );
+      //insert into field list and field combo box
+      mFieldMap.insert( fieldName, idx );
+      mExistingFieldComboBox->addItem( fieldName );
+    }
   }
 
   if ( mVectorLayer->geometryType() != QGis::NoGeometry )

src/gui/qgsfieldmodel.cpp

@@ -94,11 +94,35 @@ void QgsFieldModel::layerDeleted()
   updateModel();
 }
 
+QgsFieldModel::Filters QgsFieldModel::filters() const
+{
+  return mFilters;
+}
+
+void QgsFieldModel::setFilters( const Filters& filters )
+{
+  if ( filters == mFilters )
+    return;
+
+  mFilters = filters;
+
+  updateModel();
+}
+
 void QgsFieldModel::updateModel()
 {
   if ( mLayer )
   {
-    QgsFields newFields = mLayer->fields();
+    QgsFields fields = mLayer->fields();
+    QgsFields newFields;
+    for ( int i = 0; i < fields.count(); ++i )
+    {
+      if ( fields.fieldOrigin( i ) != QgsFields::OriginExpression && fields.fieldOrigin( i ) != QgsFields::OriginJoin )
+      {
+        newFields.append( fields.at( i ), fields.fieldOrigin( i ), fields.fieldOriginIndex( i ) );
+      }
+    }
+
     if ( mFields.toList() != newFields.toList() )
     {
       // Try to handle two special cases: addition of a new field and removal of a field.

src/gui/qgsfieldmodel.h

@@ -42,6 +42,15 @@ class GUI_EXPORT QgsFieldModel : public QAbstractItemModel
       FieldTypeRole = Qt::UserRole + 6 /*!< return the field type (if a field, return QVariant if expression) */
     };
 
+    /**
+     * Filters for which fields should be shown
+     */
+    enum Filter
+    {
+      WritableFields = 1 //!< Only show writable fields
+    };
+    Q_DECLARE_FLAGS( Filters, Filter )
+
     /**
      * @brief QgsFieldModel creates a model to display the fields of a given layer
      */
@@ -74,6 +83,16 @@ class GUI_EXPORT QgsFieldModel : public QAbstractItemModel
     int columnCount( const QModelIndex &parent ) const override;
     QVariant data( const QModelIndex &index, int role ) const override;
 
+    /**
+     * The currently applied filters that define which fields are shown.
+     */
+    Filters filters() const;
+
+    /**
+     * The currently applied filters that define which fields are shown.
+     */
+    void setFilters( const Filters& filter );
+
   public slots:
     //! set the layer of whch fields are displayed
     void setLayer( QgsVectorLayer *layer );
@@ -84,14 +103,14 @@ class GUI_EXPORT QgsFieldModel : public QAbstractItemModel
   private slots:
     void layerDeleted();
 
-  protected:
+  private:
     QgsFields mFields;
     QList<QString> mExpression;
 
     QgsVectorLayer* mLayer;
     bool mAllowExpression;
+    Filters mFilters;
 
-  private:
     void fetchFeature();
 };