Split handling of literal default values from provider side

default value SQL clauses

QgsVectorDataProvider now has two methods:

- defaultValueClause: returns SQL fragment which must be evaluated
by the provider to obtain the default value, eg sequence values
- defaultValue: returns the literal constant default value
for a field

python/core/qgsvectordataprovider.sip

@@ -226,9 +226,20 @@ class QgsVectorDataProvider : QgsDataProvider
                                  const QMap<qint64, QgsGeometry> &geometry_map );
 
     /**
-     * Returns the default value for field specified by @c fieldId
+     * Returns any literal default values which are present at the provider for a specified
+     * field index.
+     * @see defaultValueClause()
+     */
+    virtual QVariant defaultValue( int fieldIndex ) const;
+
+    /**
+     * Returns any default value clauses which are present at the provider for a specified
+     * field index. These clauses are usually SQL fragments which must be evaluated by the
+     * provider, eg sequence values.
+     * @see defaultValue()
+     * @note added in QGIS 3.0
      */
-    virtual QVariant defaultValue( int fieldId ) const;
+    virtual QString defaultValueClause( int fieldIndex ) const;
 
     /**
      * Returns any constraints which are present at the provider for a specified

src/app/qgisapp.cpp

@@ -6988,7 +6988,7 @@ void QgisApp::mergeAttributesOfSelectedFeatures()
       QgsField fld( vl->fields().at( i ) );
       bool isDefaultValue = vl->fields().fieldOrigin( i ) == QgsFields::OriginProvider &&
                             vl->dataProvider() &&
-                            vl->dataProvider()->defaultValue( vl->fields().fieldOriginIndex( i ) ) == val;
+                            vl->dataProvider()->defaultValueClause( vl->fields().fieldOriginIndex( i ) ) == val;
 
       // convert to destination data type
       if ( !isDefaultValue && !fld.convertCompatible( val ) )
@@ -7167,7 +7167,7 @@ void QgisApp::mergeSelectedFeatures()
     QVariant val = attrs.at( i );
     bool isDefaultValue = vl->fields().fieldOrigin( i ) == QgsFields::OriginProvider &&
                           vl->dataProvider() &&
-                          vl->dataProvider()->defaultValue( vl->fields().fieldOriginIndex( i ) ) == val;
+                          vl->dataProvider()->defaultValueClause( vl->fields().fieldOriginIndex( i ) ) == val;
 
     // convert to destination data type
     if ( !isDefaultValue && !vl->fields().at( i ).convertCompatible( val ) )
@@ -7481,7 +7481,7 @@ void QgisApp::editPaste( QgsMapLayer *destinationLayer )
       }
       else
       {
-        defVal = pasteVectorLayer->dataProvider()->defaultValue( dst );
+        defVal = pasteVectorLayer->dataProvider()->defaultValueClause( dst );
       }
 
       if ( defVal.isValid() && !defVal.isNull() )

src/app/qgsfeatureaction.cpp

@@ -176,7 +176,7 @@ bool QgsFeatureAction::addFeature( const QgsAttributeMap& defaultAttributes, boo
     }
     else
     {
-      v = provider->defaultValue( idx );
+      v = provider->defaultValueClause( idx );
     }
 
     mFeature->setAttribute( idx, v );

src/app/qgsidentifyresultsdialog.cpp

@@ -489,7 +489,7 @@ void QgsIdentifyResultsDialog::addFeature( QgsVectorLayer *vlayer, const QgsFeat
 
     QString defVal;
     if ( fields.fieldOrigin( i ) == QgsFields::OriginProvider && vlayer->dataProvider() )
-      defVal = vlayer->dataProvider()->defaultValue( fields.fieldOriginIndex( i ) ).toString();
+      defVal = vlayer->dataProvider()->defaultValueClause( fields.fieldOriginIndex( i ) );
 
     QString value = defVal == attrs.at( i ) ? defVal : fields.at( i ).displayString( attrs.at( i ) );
     QgsTreeWidgetItem *attrItem = new QgsTreeWidgetItem( QStringList() << QString::number( i ) << value );

src/app/qgsmergeattributesdialog.cpp

@@ -540,7 +540,7 @@ QgsAttributes QgsMergeAttributesDialog::mergedAttributes() const
       if ( !mVectorLayer->defaultValueExpression( fieldIdx ).isEmpty() )
         results[fieldIdx] = mVectorLayer->defaultValue( fieldIdx, mFeatureList.at( 0 ), &context );
       else if ( mVectorLayer->dataProvider() )
-        results[fieldIdx] = mVectorLayer->dataProvider()->defaultValue( fieldIdx );
+        results[fieldIdx] = mVectorLayer->dataProvider()->defaultValueClause( fieldIdx );
       else
         results[fieldIdx] = QVariant();
       continue;
@@ -567,7 +567,7 @@ QgsAttributes QgsMergeAttributesDialog::mergedAttributes() const
     }
     else if ( mVectorLayer->dataProvider() )
     {
-      results[fieldIdx] = mVectorLayer->dataProvider()->defaultValue( fieldIdx );
+      results[fieldIdx] = mVectorLayer->dataProvider()->defaultValueClause( fieldIdx );
     }
     widgetIndex++;
   }

src/core/qgsofflineediting.cpp

@@ -793,7 +793,7 @@ void QgsOfflineEditing::applyFeaturesAdded( QgsVectorLayer* offlineLayer, QgsVec
       if ( !remoteLayer->defaultValueExpression( k ).isEmpty() )
         newAttrs[k] = remoteLayer->defaultValue( k, f, &context );
       else if ( remoteFlds.fieldOrigin( k ) == QgsFields::OriginProvider )
-        newAttrs[k] = remoteLayer->dataProvider()->defaultValue( remoteFlds.fieldOriginIndex( k ) );
+        newAttrs[k] = remoteLayer->dataProvider()->defaultValueClause( remoteFlds.fieldOriginIndex( k ) );
     }
 
     f.setAttributes( newAttrs );

src/core/qgsvectordataprovider.cpp

@@ -98,6 +98,12 @@ QVariant QgsVectorDataProvider::defaultValue( int fieldId ) const
   return QVariant();
 }
 
+QString QgsVectorDataProvider::defaultValueClause( int fieldIndex ) const
+{
+  Q_UNUSED( fieldIndex );
+  return QString();
+}
+
 QgsFieldConstraints::Constraints QgsVectorDataProvider::fieldConstraints( int fieldIndex ) const
 {
   QgsFields f = fields();

src/core/qgsvectordataprovider.h

@@ -277,9 +277,20 @@ class CORE_EXPORT QgsVectorDataProvider : public QgsDataProvider
                                  const QgsGeometryMap &geometry_map );
 
     /**
-     * Returns the default value for field specified by @c fieldId
+     * Returns any literal default values which are present at the provider for a specified
+     * field index.
+     * @see defaultValueClause()
+     */
+    virtual QVariant defaultValue( int fieldIndex ) const;
+
+    /**
+     * Returns any default value clauses which are present at the provider for a specified
+     * field index. These clauses are usually SQL fragments which must be evaluated by the
+     * provider, eg sequence values.
+     * @see defaultValue()
+     * @note added in QGIS 3.0
      */
-    virtual QVariant defaultValue( int fieldId ) const;
+    virtual QString defaultValueClause( int fieldIndex ) const;
 
     /**
      * Returns any constraints which are present at the provider for a specified

src/core/qgsvectorlayereditutils.cpp

@@ -381,7 +381,7 @@ int QgsVectorLayerEditUtils::splitFeatures( const QList<QgsPoint>& splitLine, bo
         QgsAttributes newAttributes = feat.attributes();
         Q_FOREACH ( int pkIdx, L->dataProvider()->pkAttributeIndexes() )
         {
-          const QVariant defaultValue = L->dataProvider()->defaultValue( pkIdx );
+          const QVariant defaultValue = L->dataProvider()->defaultValueClause( pkIdx );
           if ( !defaultValue.isNull() )
           {
             newAttributes[ pkIdx ] = defaultValue;

src/gui/editorwidgets/core/qgseditorwidgetfactory.cpp

@@ -70,7 +70,7 @@ QString QgsEditorWidgetFactory::representValue( QgsVectorLayer* vl, int fieldIdx
 
   QString defVal;
   if ( vl->fields().fieldOrigin( fieldIdx ) == QgsFields::OriginProvider && vl->dataProvider() )
-    defVal = vl->dataProvider()->defaultValue( vl->fields().fieldOriginIndex( fieldIdx ) ).toString();
+    defVal = vl->dataProvider()->defaultValueClause( vl->fields().fieldOriginIndex( fieldIdx ) );
 
   return value == defVal ? defVal : vl->fields().at( fieldIdx ).displayString( value );
 }

src/gui/editorwidgets/core/qgseditorwidgetwrapper.cpp

@@ -44,7 +44,7 @@ QgsField QgsEditorWidgetWrapper::field() const
 
 QVariant QgsEditorWidgetWrapper::defaultValue() const
 {
-  mDefaultValue = layer()->dataProvider()->defaultValue( mFieldIdx );
+  mDefaultValue = layer()->dataProvider()->defaultValueClause( mFieldIdx );
 
   return mDefaultValue;
 }

src/providers/mssql/qgsmssqlprovider.cpp

@@ -433,7 +433,7 @@ void QgsMssqlProvider::loadFields()
 
         if ( !query.value( 12 ).isNull() )
         {
-          mDefaultValues.insert( i, query.value( 12 ) );
+          mDefaultValues.insert( i, query.value( 12 ).toString() );
         }
         ++i;
       }
@@ -501,12 +501,9 @@ QString QgsMssqlProvider::quotedValue( const QVariant& value )
   }
 }
 
-QVariant QgsMssqlProvider::defaultValue( int fieldId ) const
+QString QgsMssqlProvider::defaultValueClause( int fieldId ) const
 {
-  if ( mDefaultValues.contains( fieldId ) )
-    return mDefaultValues[fieldId];
-  else
-    return QVariant( QString::null );
+  return mDefaultValues.value( fieldId, QString() );
 }
 
 QString QgsMssqlProvider::storageType() const
@@ -815,7 +812,7 @@ bool QgsMssqlProvider::addFeatures( QgsFeatureList & flist )
       if ( fld.name().isEmpty() )
         continue; // invalid
 
-      if ( mDefaultValues.contains( i ) && mDefaultValues[i] == attrs.at( i ) )
+      if ( mDefaultValues.contains( i ) && mDefaultValues.value( i ) == attrs.at( i ).toString() )
         continue; // skip fields having default values
 
       if ( !first )
@@ -886,7 +883,7 @@ bool QgsMssqlProvider::addFeatures( QgsFeatureList & flist )
       if ( fld.name().isEmpty() )
         continue; // invalid
 
-      if ( mDefaultValues.contains( i ) && mDefaultValues[i] == attrs.at( i ) )
+      if ( mDefaultValues.contains( i ) && mDefaultValues.value( i ) == attrs.at( i ).toString() )
         continue; // skip fields having default values
 
       QVariant::Type type = fld.type();

src/providers/mssql/qgsmssqlprovider.h

@@ -186,7 +186,7 @@ class QgsMssqlProvider : public QgsVectorDataProvider
     //! Convert values to quoted values for database work *
     static QString quotedValue( const QVariant& value );
 
-    QVariant defaultValue( int fieldId ) const override;
+    QString defaultValueClause( int fieldId ) const override;
 
     //! Import a vector layer into the database
     static QgsVectorLayerImport::ImportError createEmptyLayer(
@@ -212,7 +212,7 @@ class QgsMssqlProvider : public QgsVectorDataProvider
 
     //! Fields
     QgsFields mAttributeFields;
-    QMap<int, QVariant> mDefaultValues;
+    QMap<int, QString> mDefaultValues;
 
     mutable QgsMssqlGeometryParser mParser;
 

src/providers/postgres/qgspostgresprovider.cpp

@@ -1716,15 +1716,27 @@ bool QgsPostgresProvider::isValid() const
   return mValid;
 }
 
+QString QgsPostgresProvider::defaultValueClause( int fieldId ) const
+{
+  QString defVal = mDefaultValues.value( fieldId, QString() );
+
+  if ( !providerProperty( EvaluateDefaultValues, false ).toBool() && !defVal.isEmpty() )
+  {
+    return defVal;
+  }
+
+  return QString();
+}
+
 QVariant QgsPostgresProvider::defaultValue( int fieldId ) const
 {
-  QVariant defVal = mDefaultValues.value( fieldId, QString::null );
+  QString defVal = mDefaultValues.value( fieldId, QString() );
 
-  if ( providerProperty( EvaluateDefaultValues, false ).toBool() && !defVal.isNull() )
+  if ( providerProperty( EvaluateDefaultValues, false ).toBool() && !defVal.isEmpty() )
   {
     QgsField fld = field( fieldId );
 
-    QgsPostgresResult res( connectionRO()->PQexec( QStringLiteral( "SELECT %1" ).arg( defVal.toString() ) ) );
+    QgsPostgresResult res( connectionRO()->PQexec( QStringLiteral( "SELECT %1" ).arg( defVal ) ) );
 
     if ( res.result() )
       return convertValue( fld.type(), fld.subType(), res.PQgetvalue( 0, 0 ) );
@@ -1735,7 +1747,7 @@ QVariant QgsPostgresProvider::defaultValue( int fieldId ) const
     }
   }
 
-  return defVal;
+  return QVariant();
 }
 
 QString QgsPostgresProvider::paramValue( const QString& fieldValue, const QString &defaultValue ) const
@@ -1891,7 +1903,7 @@ bool QgsPostgresProvider::addFeatures( QgsFeatureList &flist )
         values += delim + QStringLiteral( "$%1" ).arg( defaultValues.size() + offset );
         delim = ',';
         fieldId << idx;
-        defaultValues << defaultValue( idx ).toString();
+        defaultValues << defaultValueClause( idx );
       }
     }
 
@@ -1928,7 +1940,7 @@ bool QgsPostgresProvider::addFeatures( QgsFeatureList &flist )
 
       insert += delim + quotedIdentifier( fieldname );
 
-      QString defVal = defaultValue( idx ).toString();
+      QString defVal = defaultValueClause( idx );
 
       if ( i == flist.size() )
       {

src/providers/postgres/qgspostgresprovider.h

@@ -160,6 +160,7 @@ class QgsPostgresProvider : public QgsVectorDataProvider
     virtual bool isSaveAndLoadStyleToDBSupported() const override { return true; }
     QgsAttributeList attributeIndexes() const override;
     QgsAttributeList pkAttributeIndexes() const override { return mPrimaryKeyAttrs; }
+    QString defaultValueClause( int fieldId ) const override;
     QVariant defaultValue( int fieldId ) const override;
 
     /** Adds a list of features

tests/src/python/test_provider_postgres.py

@@ -28,6 +28,7 @@
     QgsTransactionGroup,
     QgsField,
     QgsFieldConstraints,
+    QgsDataProvider,
     NULL
 )
 from qgis.gui import QgsEditorWidgetRegistry
@@ -84,9 +85,17 @@ def partiallyCompiledFilters(self):
 
     # HERE GO THE PROVIDER SPECIFIC TESTS
     def testDefaultValue(self):
-        self.assertEqual(self.provider.defaultValue(0), 'nextval(\'qgis_test."someData_pk_seq"\'::regclass)')
+        self.provider.setProviderProperty(QgsDataProvider.EvaluateDefaultValues, True)
+        self.assertTrue(isinstance(self.provider.defaultValue(0), int))
         self.assertEqual(self.provider.defaultValue(1), NULL)
-        self.assertEqual(self.provider.defaultValue(2), '\'qgis\'::text')
+        self.assertEqual(self.provider.defaultValue(2), 'qgis')
+        self.provider.setProviderProperty(QgsDataProvider.EvaluateDefaultValues, False)
+
+    def testDefaultValueClause(self):
+        self.provider.setProviderProperty(QgsDataProvider.EvaluateDefaultValues, False)
+        self.assertEqual(self.provider.defaultValueClause(0), 'nextval(\'qgis_test."someData_pk_seq"\'::regclass)')
+        self.assertFalse(self.provider.defaultValueClause(1))
+        self.assertEqual(self.provider.defaultValueClause(2), '\'qgis\'::text')
 
     def testDateTimeTypes(self):
         vl = QgsVectorLayer('%s table="qgis_test"."date_times" sql=' % (self.dbconn), "testdatetimes", "postgres")
@@ -248,7 +257,7 @@ def testPktMapInsert(self):
         vl = QgsVectorLayer('{} table="qgis_test"."{}" key="obj_id" sql='.format(self.dbconn, 'oid_serial_table'), "oid_serial", "postgres")
         self.assertTrue(vl.isValid())
         f = QgsFeature(vl.fields())
-        f['obj_id'] = vl.dataProvider().defaultValue(0)
+        f['obj_id'] = vl.dataProvider().defaultValueClause(0)
         f['name'] = 'Test'
         r, f = vl.dataProvider().addFeatures([f])
         self.assertTrue(r)
@@ -553,17 +562,17 @@ def testKey(lyr, key, kfnames):
             oflds = olyr.fields()
             if key is None:
                 # if the pkey was not given, it will create a pkey
-                self.assertEquals(oflds.size(), flds.size() + 1)
-                self.assertEquals(oflds[0].name(), kfnames[0])
+                self.assertEqual(oflds.size(), flds.size() + 1)
+                self.assertEqual(oflds[0].name(), kfnames[0])
                 for i in range(flds.size()):
                     self.assertEqual(oflds[i + 1].name(), flds[i].name())
             else:
                 # pkey was given, no extra field generated
-                self.assertEquals(oflds.size(), flds.size())
+                self.assertEqual(oflds.size(), flds.size())
                 for i in range(oflds.size()):
                     self.assertEqual(oflds[i].name(), flds[i].name())
             pks = olyr.pkAttributeList()
-            self.assertEquals(len(pks), len(kfnames))
+            self.assertEqual(len(pks), len(kfnames))
             for i in range(0, len(kfnames)):
                 self.assertEqual(oflds[pks[i]].name(), kfnames[i])
 

tests/src/python/test_qgsrelationeditwidget.py

@@ -153,7 +153,7 @@ def test_link_feature(self):
         wrapper = self.createWrapper(self.vl_a, '"name"=\'Douglas Adams\'')  # NOQA
 
         f = QgsFeature(self.vl_b.fields())
-        f.setAttributes([self.vl_b.dataProvider().defaultValue(0), 'The Hitchhiker\'s Guide to the Galaxy'])
+        f.setAttributes([self.vl_b.dataProvider().defaultValueClause(0), 'The Hitchhiker\'s Guide to the Galaxy'])
         self.vl_b.addFeature(f)
 
         def choose_linked_feature():
@@ -318,7 +318,7 @@ def addFeature(self, layer, defaultValues, defaultGeometry):
             if v:
                 values.append(v)
             else:
-                values.append(layer.dataProvider().defaultValue(i))
+                values.append(layer.dataProvider().defaultValueClause(i))
         f = QgsFeature(layer.fields())
         f.setAttributes(self.values)
         f.setGeometry(defaultGeometry)