When loading a QLR, try to match the layer name if id does not

python/core/auto_generated/fieldformatter/qgsvaluerelationfieldformatter.sip.in

@@ -121,6 +121,15 @@ Check whether the ``feature`` has all values required by the ``expression``
 .. versionadded:: 3.2
 %End
 
+    static QgsVectorLayer *resolveLayer( const QVariantMap &config );
+%Docstring
+Returns the (possibly NULL) layer from the widget's ``config``
+
+.. versionadded:: 3.8
+%End
+
+
+
 };
 
 

python/core/auto_generated/qgsmaplayer.sip.in

@@ -1260,6 +1260,14 @@ The storage format for the XML is qlr
 .. versionadded:: 3.6
 %End
 
+    static QString generateId( const QString &layerName );
+%Docstring
+Generates an unique identifier for this layer, the generate ID is prefixed by ``layerName``
+
+.. versionadded:: 3.8
+%End
+
+
   public slots:
 
     void setMinimumScale( double scale );

src/core/fieldformatter/qgsvaluerelationfieldformatter.cpp

@@ -118,7 +118,7 @@ QgsValueRelationFieldFormatter::ValueRelationCache QgsValueRelationFieldFormatte
 {
   ValueRelationCache cache;
 
-  QgsVectorLayer *layer = QgsProject::instance()->mapLayer<QgsVectorLayer *>( config.value( QStringLiteral( "Layer" ) ).toString() );
+  const QgsVectorLayer *layer = resolveLayer( config );
 
   if ( !layer )
     return cache;
@@ -273,3 +273,26 @@ bool QgsValueRelationFieldFormatter::expressionIsUsable( const QString &expressi
     return false;
   return true;
 }
+
+QgsVectorLayer *QgsValueRelationFieldFormatter::resolveLayer( const QVariantMap &config )
+{
+  QgsVectorLayer *layer { QgsProject::instance()->mapLayer<QgsVectorLayer *>( config.value( QStringLiteral( "Layer" ) ).toString() ) };
+  if ( ! layer )
+  {
+    const auto name { config.value( QStringLiteral( "LayerName" ) ).toString() };
+    if ( ! name.isEmpty() )
+    {
+      const auto constLayers { QgsProject::instance()->mapLayers( true ) };
+      for ( QgsMapLayer *l : constLayers )
+      {
+        QgsVectorLayer *vl { qobject_cast<QgsVectorLayer *>( l ) };
+        if ( vl && vl->name() == name )
+        {
+          layer = vl;
+        }
+      }
+    }
+  }
+  return layer;
+}
+

src/core/fieldformatter/qgsvaluerelationfieldformatter.h

@@ -119,6 +119,14 @@ class CORE_EXPORT QgsValueRelationFieldFormatter : public QgsFieldFormatter
      */
     static bool expressionIsUsable( const QString &expression, const QgsFeature &feature );
 
+    /**
+     * Returns the (possibly NULL) layer from the widget's \a config
+     * \since QGIS 3.8
+     */
+    static QgsVectorLayer *resolveLayer( const QVariantMap &config );
+
+
+
 };
 
 Q_DECLARE_METATYPE( QgsValueRelationFieldFormatter::ValueRelationCache )

src/core/qgslayerdefinition.cpp

@@ -87,26 +87,25 @@ bool QgsLayerDefinition::loadLayerDefinition( QDomDocument doc, QgsProject *proj
 
   // IDs of layers should be changed otherwise we may have more then one layer with the same id
   // We have to replace the IDs before we load them because it's too late once they are loaded
-  QDomNodeList ids = doc.elementsByTagName( QStringLiteral( "id" ) );
-  for ( int i = 0; i < ids.size(); ++i )
+  QDomNodeList treeLayerNodes = doc.elementsByTagName( QStringLiteral( "layer-tree-layer" ) );
+  for ( int i = 0; i < treeLayerNodes.size(); ++i )
   {
-    QDomNode idnode = ids.at( i );
-    QDomElement idElem = idnode.toElement();
-    QString oldid = idElem.text();
-    // Strip the date part because we will replace it.
-    QString layername = oldid.left( oldid.length() - 17 );
-    QDateTime dt = QDateTime::currentDateTime();
-    QString newid = layername + dt.toString( QStringLiteral( "yyyyMMddhhmmsszzz" ) ) + QString::number( qrand() );
-    idElem.firstChild().setNodeValue( newid );
-    QDomNodeList treeLayerNodes = doc.elementsByTagName( QStringLiteral( "layer-tree-layer" ) );
-
-    for ( int i = 0; i < treeLayerNodes.count(); ++i )
+    QDomNode treeLayerNode = treeLayerNodes.at( i );
+    QDomElement treeLayerElem = treeLayerNode.toElement();
+    QString oldid = treeLayerElem.attribute( QStringLiteral( "id" ) );
+    QString layername = treeLayerElem.attribute( QStringLiteral( "name" ) );
+    QString newid = QgsMapLayer::generateId( layername );
+    treeLayerElem.setAttribute( QStringLiteral( "id" ), newid );
+
+    // Replace IDs for map layers
+    QDomNodeList ids = doc.elementsByTagName( QStringLiteral( "id" ) );
+    for ( int i = 0; i < ids.size(); ++i )
     {
-      QDomNode layerNode = treeLayerNodes.at( i );
-      QDomElement layerElem = layerNode.toElement();
-      if ( layerElem.attribute( QStringLiteral( "id" ) ) == oldid )
+      QDomNode idnode = ids.at( i );
+      QDomElement idElem = idnode.toElement();
+      if ( idElem.text() == oldid )
       {
-        layerNode.toElement().setAttribute( QStringLiteral( "id" ), newid );
+        idElem.firstChild().setNodeValue( newid );
       }
     }
 
@@ -137,6 +136,28 @@ bool QgsLayerDefinition::loadLayerDefinition( QDomDocument doc, QgsProject *proj
       }
     }
 
+    // Change IDs of widget config values
+    QDomNodeList widgetConfig = doc.elementsByTagName( QStringLiteral( "editWidget" ) );
+    for ( int i = 0; i < widgetConfig.size(); i++ )
+    {
+      QDomNodeList config = widgetConfig.at( i ).childNodes();
+      for ( int j = 0; j < config.size(); j++ )
+      {
+        QDomNodeList optMap = config.at( j ).childNodes();
+        for ( int z = 0; z < optMap.size(); z++ )
+        {
+          QDomNodeList opts = optMap.at( z ).childNodes();
+          for ( int k = 0; k < opts.size(); k++ )
+          {
+            QDomElement opt = opts.at( k ).toElement();
+            if ( opt.attribute( QStringLiteral( "value" ) ) == oldid )
+            {
+              opt.setAttribute( QStringLiteral( "value" ), newid );
+            }
+          }
+        }
+      }
+    }
   }
 
   QDomElement layerTreeElem = doc.documentElement().firstChildElement( QStringLiteral( "layer-tree-group" ) );

src/core/qgsmaplayer.cpp

@@ -78,24 +78,9 @@ QgsMapLayer::QgsMapLayer( QgsMapLayerType type,
   , mStyleManager( new QgsMapLayerStyleManager( this ) )
   , mRefreshTimer( new QTimer( this ) )
 {
-  //mShortName.replace( QRegExp( "[\\W]" ), "_" );
-
-  // Generate the unique ID of this layer
-  QString uuid = QUuid::createUuid().toString();
-  // trim { } from uuid
-  mID = lyrname + '_' + uuid.mid( 1, uuid.length() - 2 );
-
-  // Tidy the ID up to avoid characters that may cause problems
-  // elsewhere (e.g in some parts of XML). Replaces every non-word
-  // character (word characters are the alphabet, numbers and
-  // underscore) with an underscore.
-  // Note that the first backslashe in the regular expression is
-  // there for the compiler, so the pattern is actually \W
-  mID.replace( QRegExp( "[\\W]" ), QStringLiteral( "_" ) );
-
+  mID = generateId( lyrname );
   connect( this, &QgsMapLayer::crsChanged, this, &QgsMapLayer::configChanged );
   connect( this, &QgsMapLayer::nameChanged, this, &QgsMapLayer::configChanged );
-
   connect( mRefreshTimer, &QTimer::timeout, this, [ = ] { triggerRepaint( true ); } );
 }
 
@@ -1876,6 +1861,22 @@ void QgsMapLayer::setOriginalXmlProperties( const QString &originalXmlProperties
   mOriginalXmlProperties = originalXmlProperties;
 }
 
+QString QgsMapLayer::generateId( const QString &layerName )
+{
+  // Generate the unique ID of this layer
+  QString uuid = QUuid::createUuid().toString();
+  // trim { } from uuid
+  QString id = layerName + '_' + uuid.mid( 1, uuid.length() - 2 );
+  // Tidy the ID up to avoid characters that may cause problems
+  // elsewhere (e.g in some parts of XML). Replaces every non-word
+  // character (word characters are the alphabet, numbers and
+  // underscore) with an underscore.
+  // Note that the first backslash in the regular expression is
+  // there for the compiler, so the pattern is actually \W
+  id.replace( QRegExp( "[\\W]" ), QStringLiteral( "_" ) );
+  return id;
+}
+
 void QgsMapLayer::setProviderType( const QString &providerType )
 {
   mProviderKey = providerType;

src/core/qgsmaplayer.h

@@ -1133,6 +1133,13 @@ class CORE_EXPORT QgsMapLayer : public QObject
      */
     void setOriginalXmlProperties( const QString &originalXmlProperties );
 
+    /**
+     * Generates an unique identifier for this layer, the generate ID is prefixed by \a layerName
+     * \since QGIS 3.8
+     */
+    static QString generateId( const QString &layerName );
+
+
   public slots:
 
     /**

src/gui/editorwidgets/qgsvaluerelationconfigdlg.cpp

@@ -18,6 +18,7 @@
 #include "qgsvectorlayer.h"
 #include "qgsexpressionbuilderdialog.h"
 #include "qgsexpressioncontextutils.h"
+#include "qgsvaluerelationfieldformatter.h"
 
 QgsValueRelationConfigDlg::QgsValueRelationConfigDlg( QgsVectorLayer *vl, int fieldIdx, QWidget *parent )
   : QgsEditorConfigWidget( vl, fieldIdx, parent )
@@ -55,6 +56,7 @@ QVariantMap QgsValueRelationConfigDlg::config()
   QVariantMap cfg;
 
   cfg.insert( QStringLiteral( "Layer" ), mLayerName->currentLayer() ? mLayerName->currentLayer()->id() : QString() );
+  cfg.insert( QStringLiteral( "LayerName" ), mLayerName->currentLayer() ? mLayerName->currentLayer()->name() : QString() );
   cfg.insert( QStringLiteral( "Key" ), mKeyColumn->currentField() );
   cfg.insert( QStringLiteral( "Value" ), mValueColumn->currentField() );
   cfg.insert( QStringLiteral( "AllowMulti" ), mAllowMulti->isChecked() );
@@ -69,7 +71,7 @@ QVariantMap QgsValueRelationConfigDlg::config()
 
 void QgsValueRelationConfigDlg::setConfig( const QVariantMap &config )
 {
-  QgsVectorLayer *lyr = QgsProject::instance()->mapLayer<QgsVectorLayer *>( config.value( QStringLiteral( "Layer" ) ).toString() );
+  QgsVectorLayer *lyr = QgsValueRelationFieldFormatter::resolveLayer( config );
   mLayerName->setLayer( lyr );
   mKeyColumn->setField( config.value( QStringLiteral( "Key" ) ).toString() );
   mValueColumn->setField( config.value( QStringLiteral( "Value" ) ).toString() );

src/gui/editorwidgets/qgsvaluerelationwidgetwrapper.cpp

@@ -299,9 +299,10 @@ int QgsValueRelationWidgetWrapper::columnCount() const
   return std::max( 1, config( QStringLiteral( "NofColumns" ) ).toInt() );
 }
 
+
 QVariant::Type QgsValueRelationWidgetWrapper::fkType() const
 {
-  QgsVectorLayer *layer = QgsProject::instance()->mapLayer<QgsVectorLayer *>( config().value( QStringLiteral( "Layer" ) ).toString() );
+  const QgsVectorLayer *layer = QgsValueRelationFieldFormatter::resolveLayer( config() );
   if ( layer )
   {
     QgsFields fields = layer->fields();

tests/src/gui/testqgsvaluerelationwidgetwrapper.cpp

@@ -53,6 +53,7 @@ class TestQgsValueRelationWidgetWrapper : public QObject
     void testWithJsonInGPKG();
     void testWithJsonInSpatialite();
     void testWithJsonInSpatialiteTextFk();
+    void testMatchLayerName();
 };
 
 void TestQgsValueRelationWidgetWrapper::initTestCase()
@@ -921,5 +922,58 @@ void TestQgsValueRelationWidgetWrapper::testWithJsonInSpatialiteTextFk()
 
 }
 
+void TestQgsValueRelationWidgetWrapper::testMatchLayerName()
+{
+  // create a vector layer
+  QgsVectorLayer vl1( QStringLiteral( "Polygon?crs=epsg:4326&field=pk:int&field=province:int&field=municipality:string" ), QStringLiteral( "vl1" ), QStringLiteral( "memory" ) );
+  QgsVectorLayer vl2( QStringLiteral( "Point?crs=epsg:4326&field=pk:int&field=fk_province:int&field=fk_municipality:int" ), QStringLiteral( "vl2" ), QStringLiteral( "memory" ) );
+  QgsProject::instance()->addMapLayer( &vl1, false, false );
+  QgsProject::instance()->addMapLayer( &vl2, false, false );
+
+  // insert some features
+  QgsFeature f1( vl1.fields() );
+  f1.setAttribute( QStringLiteral( "pk" ), 0 );  // !!! Notice: pk 0
+  f1.setAttribute( QStringLiteral( "province" ), 123 );
+  f1.setAttribute( QStringLiteral( "municipality" ), QStringLiteral( "Some Place By The River" ) );
+  f1.setGeometry( QgsGeometry::fromWkt( QStringLiteral( "POLYGON(( 0 0, 0 1, 1 1, 1 0, 0 0 ))" ) ) );
+  QVERIFY( f1.isValid() );
+  QgsFeature f2( vl1.fields() );
+  f2.setAttribute( QStringLiteral( "pk" ), 2 );
+  f2.setAttribute( QStringLiteral( "province" ), 245 );
+  f2.setAttribute( QStringLiteral( "municipality" ), QStringLiteral( "Dreamland By The Clouds" ) );
+  f2.setGeometry( QgsGeometry::fromWkt( QStringLiteral( "POLYGON(( 1 0, 1 1, 2 1, 2 0, 1 0 ))" ) ) );
+  QVERIFY( f2.isValid() );
+  QVERIFY( vl1.dataProvider()->addFeatures( QgsFeatureList() << f1 << f2 ) );
+
+  QgsFeature f3( vl2.fields() );
+  f3.setAttribute( QStringLiteral( "fk_province" ), 123 );
+  f3.setAttribute( QStringLiteral( "fk_municipality" ), QStringLiteral( "0" ) );
+  f3.setGeometry( QgsGeometry::fromWkt( QStringLiteral( "POINT( 0.5 0.5)" ) ) );
+  QVERIFY( f3.isValid() );
+  QVERIFY( f3.geometry().isGeosValid() );
+  QVERIFY( vl2.dataProvider()->addFeature( f3 ) );
+
+  // build a value relation widget wrapper for municipality
+  QgsValueRelationWidgetWrapper w_municipality( &vl2, vl2.fields().indexOf( QStringLiteral( "fk_municipality" ) ), nullptr, nullptr );
+  QVariantMap cfg_municipality;
+  cfg_municipality.insert( QStringLiteral( "Layer" ), QStringLiteral( "wrong_id_here_hope_name_is_good" ) );
+  cfg_municipality.insert( QStringLiteral( "LayerName" ), vl1.name() );
+  cfg_municipality.insert( QStringLiteral( "Key" ),  QStringLiteral( "pk" ) );
+  cfg_municipality.insert( QStringLiteral( "Value" ), QStringLiteral( "municipality" ) );
+  cfg_municipality.insert( QStringLiteral( "AllowMulti" ), false );
+  cfg_municipality.insert( QStringLiteral( "NofColumns" ), 1 );
+  cfg_municipality.insert( QStringLiteral( "AllowNull" ), true );
+  cfg_municipality.insert( QStringLiteral( "OrderByValue" ), false );
+  cfg_municipality.insert( QStringLiteral( "UseCompleter" ), false );
+  w_municipality.setConfig( cfg_municipality );
+  w_municipality.widget();
+  w_municipality.setEnabled( true );
+
+  w_municipality.setValue( 0 );
+  QCOMPARE( w_municipality.mComboBox->currentIndex(), 1 );
+  QCOMPARE( w_municipality.mComboBox->currentText(), QStringLiteral( "Some Place By The River" ) );
+
+}
+
 QGSTEST_MAIN( TestQgsValueRelationWidgetWrapper )
 #include "testqgsvaluerelationwidgetwrapper.moc"