Forward databaseConnection to parent item for layer items

... and preset SQL in query dialog

python/core/auto_generated/browser/qgslayeritem.sip.in

@@ -140,6 +140,8 @@ Returns icon for point cloud layer
 
 :return: the layer name
 %End
+    virtual QgsAbstractDatabaseProviderConnection *databaseConnection() const;
+
 
 };
 

src/app/browser/qgsinbuiltdataitemproviders.cpp

@@ -1060,32 +1060,62 @@ void QgsDatabaseItemGuiProvider::populateContextMenu( QgsDataItem *item, QMenu *
         } );
         menu->addAction( newTableAction );
       }
+    }
+
+    // SQL dialog
+    if ( item->databaseConnection() )
+    {
+      std::unique_ptr<QgsAbstractDatabaseProviderConnection> conn( item->databaseConnection() );
 
       if ( conn && conn->capabilities().testFlag( QgsAbstractDatabaseProviderConnection::Capability::ExecuteSql ) )
       {
 
         QAction *sqlAction = new QAction( QObject::tr( "Run SQL command…" ), menu );
 
-        QObject::connect( sqlAction, &QAction::triggered, collectionItem, [ collectionItem, context ]
+        QObject::connect( sqlAction, &QAction::triggered, item, [ item, context ]
         {
-          std::unique_ptr<QgsAbstractDatabaseProviderConnection> conn2( collectionItem->databaseConnection() );
+          std::unique_ptr<QgsAbstractDatabaseProviderConnection> conn2( item->databaseConnection() );
           // This should never happen but let's play safe
           if ( ! conn2 )
           {
-            QgsMessageLog::logMessage( tr( "Connection to the database (%1) was lost." ).arg( collectionItem->name() ) );
+            QgsMessageLog::logMessage( tr( "Connection to the database (%1) was lost." ).arg( item->name() ) );
             return;
           }
+
+          // Create the SQL dialog: this might become an independent class dialog in the future, for now
+          // we are still prototyping the features that this dialog will have.
+
           QgsDialog dialog;
           dialog.setObjectName( QStringLiteral( "SQLCommandsDialog" ) );
-          dialog.setWindowTitle( tr( "%1 — Run SQL Commands" ).arg( collectionItem->name() ) );
+          dialog.setWindowTitle( tr( "%1 — Run SQL Commands" ).arg( item->name() ) );
+
+          // If this is a layer item (or below the hierarchy) we can pre-set the query to something
+          // meaningful
+          QString sql;
+
+          if ( qobject_cast<QgsLayerItem *>( item ) )
+          {
+            if ( conn2->capabilities().testFlag( QgsAbstractDatabaseProviderConnection::Capability::Schemas ) )
+            {
+              // Ok, this is gross: we lack a connection API for quoting properly...
+              sql = QStringLiteral( "SELECT * FROM %1.%2 LIMIT 10" ).arg( QgsSqliteUtils::quotedIdentifier( item->parent()->name() ), QgsSqliteUtils::quotedIdentifier( item->name() ) );
+            }
+            else
+            {
+              // Ok, this is gross: we lack a connection API for quoting properly...
+              sql = QStringLiteral( "SELECT * FROM %1 LIMIT 10" ).arg( QgsSqliteUtils::quotedIdentifier( item->name() ) );
+            }
+          }
+
           QgsGui::enableAutoGeometryRestore( &dialog );
           QgsQueryResultWidget *widget { new QgsQueryResultWidget( &dialog, conn2.release() ) };
+          widget->setQuery( sql );
           widget->layout()->setMargin( 0 );
           dialog.layout()->addWidget( widget );
 
-          connect( widget, &QgsQueryResultWidget::createSqlVectorLayer, widget, [ collectionItem, context ]( const QString &, const QString &, const QgsAbstractDatabaseProviderConnection::SqlVectorLayerOptions & options )
+          connect( widget, &QgsQueryResultWidget::createSqlVectorLayer, widget, [ item, context ]( const QString &, const QString &, const QgsAbstractDatabaseProviderConnection::SqlVectorLayerOptions & options )
           {
-            std::unique_ptr<QgsAbstractDatabaseProviderConnection> conn3( collectionItem->databaseConnection() );
+            std::unique_ptr<QgsAbstractDatabaseProviderConnection> conn3( item->databaseConnection() );
             try
             {
               QgsMapLayer *sqlLayer { conn3->createSqlVectorLayer( options ) };
@@ -1098,6 +1128,8 @@ void QgsDatabaseItemGuiProvider::populateContextMenu( QgsDataItem *item, QMenu *
 
           } );
           dialog.exec();
+
+
         } );
         menu->addAction( sqlAction );
       }

src/core/browser/qgslayeritem.cpp

@@ -66,6 +66,15 @@ QIcon QgsLayerItem::iconPointCloud()
   return QgsIconUtils::iconPointCloud();
 }
 
+QgsAbstractDatabaseProviderConnection *QgsLayerItem::databaseConnection() const
+{
+  if ( parent() )
+  {
+    return parent()->databaseConnection();
+  }
+  return nullptr;
+}
+
 QIcon QgsLayerItem::iconDefault()
 {
   return QgsIconUtils::iconDefaultLayer();

src/core/browser/qgslayeritem.h

@@ -140,6 +140,7 @@ class CORE_EXPORT QgsLayerItem : public QgsDataItem
     static QIcon iconPointCloud();
     //! \returns the layer name
     virtual QString layerName() const { return name(); }
+    QgsAbstractDatabaseProviderConnection *databaseConnection() const override;
 
 };