[FEATURE] Detect default literal values from OGR layers

Requires GDAL >= 2

Author: nyalldawson

src/providers/ogr/qgsogrprovider.cpp

@@ -840,6 +840,7 @@ void QgsOgrProvider::loadFields()
   QgsOgrConnPool::instance()->invalidateConnections( dataSourceUri() );
   //the attribute fields need to be read again when the encoding changes
   mAttributeFields.clear();
+  mDefaultValues.clear();
   if ( !ogrLayer )
     return;
 
@@ -947,6 +948,13 @@ void QgsOgrProvider::loadFields()
         constraints.setConstraint( QgsFieldConstraints::ConstraintNotNull, QgsFieldConstraints::ConstraintOriginProvider );
         newField.setConstraints( constraints );
       }
+
+      // check if field has default value
+      QString defaultValue = textEncoding()->toUnicode( OGR_Fld_GetDefault( fldDef ) );
+      if ( !defaultValue.isEmpty() && !OGR_Fld_IsDefaultDriverSpecific( fldDef ) )
+      {
+        mDefaultValues.insert( i + ( mFirstFieldIsFid ? 1 : 0 ), defaultValue );
+      }
 #endif
 
       mAttributeFields.append( newField );
@@ -1081,6 +1089,34 @@ QgsRectangle QgsOgrProvider::extent() const
   return mExtentRect;
 }
 
+QVariant QgsOgrProvider::defaultValue( int fieldId ) const
+{
+  if ( fieldId < 0 || fieldId >= mAttributeFields.count() )
+    return QVariant();
+
+  QString defaultVal = mDefaultValues.value( fieldId, QString() );
+  if ( defaultVal.isEmpty() )
+    return QVariant();
+
+  QVariant resultVar = defaultVal;
+  if ( defaultVal == QStringLiteral( "CURRENT_TIMESTAMP" ) )
+    resultVar = QDateTime::currentDateTime();
+  else if ( defaultVal == QStringLiteral( "CURRENT_DATE" ) )
+    resultVar = QDate::currentDate();
+  else if ( defaultVal == QStringLiteral( "CURRENT_TIME" ) )
+    resultVar = QTime::currentTime();
+  else if ( defaultVal.startsWith( '\'' ) )
+  {
+    defaultVal = defaultVal.remove( 0, 1 );
+    defaultVal.chop( 1 );
+    defaultVal.replace( "''", "'" );
+    resultVar = defaultVal;
+  }
+
+  ( void )mAttributeFields.at( fieldId ).convertCompatible( resultVar );
+  return resultVar;
+}
+
 void QgsOgrProvider::updateExtents()
 {
   invalidateCachedExtent( true );

src/providers/ogr/qgsogrprovider.h

@@ -124,6 +124,8 @@ class QgsOgrProvider : public QgsVectorDataProvider
 
     virtual QgsRectangle extent() const override;
 
+    QVariant defaultValue( int fieldId ) const override;
+
     /** Update the extents
      */
     virtual void updateExtents() override;
@@ -297,7 +299,12 @@ class QgsOgrProvider : public QgsVectorDataProvider
   private:
     unsigned char *getGeometryPointer( OGRFeatureH fet );
     QString ogrWkbGeometryTypeName( OGRwkbGeometryType type ) const;
+
     QgsFields mAttributeFields;
+
+    //! Map of field index to default value
+    QMap<int, QString> mDefaultValues;
+
     bool mFirstFieldIsFid;
     OGRDataSourceH ogrDataSource;
     mutable OGREnvelope* mExtent;

tests/src/python/test_provider_ogr_sqlite.py

@@ -20,9 +20,10 @@
 import glob
 from osgeo import gdal, ogr
 
-from qgis.core import QgsVectorLayer, QgsFeature, QgsGeometry, QgsFeatureRequest, QgsField, QgsFieldConstraints
+from qgis.core import QgsVectorLayer, QgsFeature, QgsGeometry, QgsFeatureRequest, QgsField, QgsFieldConstraints, NULL
 from qgis.testing import start_app, unittest
 from utilities import unitTestDataPath
+from qgis.PyQt.QtCore import QDate, QTime, QDateTime
 
 start_app()
 
@@ -160,6 +161,48 @@ def testNotNullConstraint(self):
         self.assertTrue(fields.at(2).constraints().constraints() & QgsFieldConstraints.ConstraintNotNull)
         self.assertEqual(fields.at(2).constraints().constraintOrigin(QgsFieldConstraints.ConstraintNotNull), QgsFieldConstraints.ConstraintOriginProvider)
 
+    @unittest.expectedFailure(int(gdal.VersionInfo('VERSION_NUM')) < GDAL_COMPUTE_VERSION(2, 0, 0))
+    def testDefaultValues(self):
+        """ test detection of defaults on OGR layer """
+
+        tmpfile = os.path.join(self.basetestpath, 'testDefaults.sqlite')
+        ds = ogr.GetDriverByName('SQLite').CreateDataSource(tmpfile)
+        lyr = ds.CreateLayer('test', geom_type=ogr.wkbPoint, options=['FID=fid'])
+        lyr.CreateField(ogr.FieldDefn('field1', ogr.OFTInteger))
+        fld2 = ogr.FieldDefn('field2', ogr.OFTInteger)
+        fld2.SetDefault('5')
+        lyr.CreateField(fld2)
+        fld3 = ogr.FieldDefn('field3', ogr.OFTString)
+        fld3.SetDefault("'some ''default'")
+        lyr.CreateField(fld3)
+        fld4 = ogr.FieldDefn('field4', ogr.OFTDate)
+        fld4.SetDefault("CURRENT_DATE")
+        lyr.CreateField(fld4)
+        fld5 = ogr.FieldDefn('field5', ogr.OFTTime)
+        fld5.SetDefault("CURRENT_TIME")
+        lyr.CreateField(fld5)
+        fld6 = ogr.FieldDefn('field6', ogr.OFTDateTime)
+        fld6.SetDefault("CURRENT_TIMESTAMP")
+        lyr.CreateField(fld6)
+
+        ds = None
+
+        vl = QgsVectorLayer('{}'.format(tmpfile), 'test', 'ogr')
+        self.assertTrue(vl.isValid())
+
+        # test some bad indexes
+        self.assertFalse(vl.dataProvider().defaultValue(-1))
+        self.assertFalse(vl.dataProvider().defaultValue(1001))
+
+        # test default
+        self.assertEqual(vl.dataProvider().defaultValue(1), NULL)
+        self.assertEqual(vl.dataProvider().defaultValue(2), 5)
+        self.assertEqual(vl.dataProvider().defaultValue(3), "some 'default")
+        self.assertEqual(vl.dataProvider().defaultValue(4), QDate.currentDate())
+        # time may pass, so we allow 1 second difference here
+        self.assertTrue(vl.dataProvider().defaultValue(5).secsTo(QTime.currentTime()) < 1)
+        self.assertTrue(vl.dataProvider().defaultValue(6).secsTo(QDateTime.currentDateTime()) < 1)
+
 
 if __name__ == '__main__':
     unittest.main()