Merge pull request #3665 from rouault/save_style_gpkg

 [FEATURE] [OGR provider] Load/save style in database for GPKG and Spatialite

Author: rouault

doc/api_break.dox

@@ -1438,6 +1438,9 @@ displayExpression instead. For the map tip use mapTipTemplate() instead.</li>
 <li>Removed fieldNameIndex(), use fields().lookupField() or fields().indexFromName() instead
 <li>Renamed addAttributeAlias() to setFieldAlias()
 <li>Renamed remAttributeAlias() to removeFieldAlias()
+<li>saveStyleToDatabase(): msgError argument is correctly declared as output argument
+<li>getStyleFromDatabase(): msgError argument is correctly declared as output argument
+<li>loadNamedStyle(): theResultFlag argument is correctly declared as output argument
 </ul>
 
 \subsection qgis_api_break_3_0_QgsVectorLayerEditBuffer QgsVectorLayerEditBuffer

python/core/qgsvectorlayer.sip

@@ -662,11 +662,11 @@ class QgsVectorLayer : QgsMapLayer
      * @param description
      * @param useAsDefault
      * @param uiFileContent
-     * @param msgError
+     * @param msgError (out)
      */
     virtual void saveStyleToDatabase( const QString& name, const QString& description,
                                       bool useAsDefault, const QString& uiFileContent,
-                                      QString &msgError );
+                                      QString &msgError /Out/ );
 
     /**
      * Lists all the style in db split into related to the layer and not related to
@@ -682,21 +682,21 @@ class QgsVectorLayer : QgsMapLayer
     /**
      * Will return the named style corresponding to style id provided
      */
-    virtual QString getStyleFromDatabase( const QString& styleId, QString &msgError );
+    virtual QString getStyleFromDatabase( const QString& styleId, QString &msgError /Out/ );
 
     /**
      * Load a named style from file/local db/datasource db
      * @param theURI the URI of the style or the URI of the layer
      * @param theResultFlag will be set to true if a named style is correctly loaded
      * @param loadFromLocalDb if true forces to load from local db instead of datasource one
      */
-    virtual QString loadNamedStyle( const QString &theURI, bool &theResultFlag, bool loadFromLocalDb );
+    virtual QString loadNamedStyle( const QString &theURI, bool &theResultFlag /Out/, bool loadFromLocalDb );
 
     /**
      * Calls loadNamedStyle( theURI, theResultFlag, false );
      * Retained for backward compatibility
      */
-    virtual QString loadNamedStyle( const QString &theURI, bool &theResultFlag );
+    virtual QString loadNamedStyle( const QString &theURI, bool &theResultFlag /Out/ );
 
     /** Read the symbology for the current layer from the Dom node supplied.
      * @param node node that will contain the symbology definition for this layer.

src/core/qgsvectorlayer.cpp

@@ -1947,7 +1947,14 @@ bool QgsVectorLayer::writeSymbology( QDomNode& node, QDomDocument& doc, QString&
   mConditionalStyles->writeXml( node, doc );
 
   // save expression fields
-  mExpressionFieldBuffer->writeXml( node, doc );
+  if ( !mExpressionFieldBuffer )
+  {
+    // can happen when saving style on a invalid layer
+    QgsExpressionFieldBuffer dummy;
+    dummy.writeXml( node, doc );
+  }
+  else
+    mExpressionFieldBuffer->writeXml( node, doc );
 
   // save readonly state
   node.toElement().setAttribute( QStringLiteral( "readOnly" ), mReadOnly );
@@ -4107,7 +4114,7 @@ QString QgsVectorLayer::loadNamedStyle( const QString &theURI, bool &theResultFl
 QString QgsVectorLayer::loadNamedStyle( const QString &theURI, bool &theResultFlag, bool loadFromLocalDB )
 {
   QgsDataSourceUri dsUri( theURI );
-  if ( !loadFromLocalDB && !dsUri.database().isEmpty() )
+  if ( !loadFromLocalDB && mDataProvider && mDataProvider->isSaveAndLoadStyleToDBSupported() )
   {
     QgsProviderRegistry * pReg = QgsProviderRegistry::instance();
     QLibrary *myLib = pReg->providerLibrary( mProviderKey );