26 #include <QStringListModel>    71     return fieldName + 
" IS NULL";
    73     return fieldName + 
" IS NOT NULL";
    83     case QVariant::Double:
    84     case QVariant::LongLong:
    85     case QVariant::ULongLong:
    88         return fieldName + 
'=' + v.toString();
    90         return fieldName + 
"<>" + v.toString();
    97         return fieldName + 
"='" + v.toString() + 
'\'';
    99         return fieldName + 
"<>'" + v.toString() + 
'\'';
   119     mWidget->setEnabled( enabled );
   130   if ( !value.isValid() )
   151   if ( exp == nullValue )
   153     str = QStringLiteral( 
"%1 IS NULL" ).arg( QgsExpression::quotedColumnRef( fieldName ) );
   157     str = QStringLiteral( 
"%1 = '%3'" )
   158           .arg( QgsExpression::quotedColumnRef( fieldName ),
   159                 exp.replace( 
'\'', QLatin1String( 
"''" ) )
   185   if ( 
config( QStringLiteral( 
"FilterFields" ), QVariant() ).isValid() )
 
This class is a composition of two QSettings instances: 
 
Map canvas is a class for displaying all GIS data types on a canvas. 
 
QgsField at(int i) const
Get field at particular index (must be in range 0..N-1) 
 
QgsFields fields() const override
Returns the list of fields of this layer. 
 
static QString nullRepresentation()
This string is used to represent the value NULL throughout QGIS. 
 
QgsRelationManager relationManager
 
static QgsProject * instance()
Returns the QgsProject singleton instance. 
 
Q_INVOKABLE QgsRelation relation(const QString &id) const
Get access to a relation by its id. 
 
Represents a vector layer which manages a vector based data sets.