[mssql] Prevent overwriting existing tables via drag and drop in browser

Fixes #16805

src/providers/mssql/qgsmssqlprovider.cpp

@@ -1819,6 +1819,26 @@ QgsVectorLayerExporter::ExportError QgsMssqlProvider::createEmptyLayer( const QS
       return QgsVectorLayerExporter::ErrCreateLayer;
     }
   }
+  else
+  {
+    // test for existing
+    sql = QStringLiteral( "SELECT * FROM sys.objects WHERE object_id = OBJECT_ID(N'[%1].[%2]') AND type in (N'U')" )
+          .arg( schemaName, tableName );
+    if ( !q.exec( sql ) )
+    {
+      if ( errorMessage )
+        *errorMessage = q.lastError().text();
+      return QgsVectorLayerExporter::ErrCreateLayer;
+    }
+
+    // if we got a hit, abort!!
+    if ( q.next() )
+    {
+      if ( errorMessage )
+        *errorMessage = tr( "Table [%1].[%2] already exists" ).arg( schemaName, tableName );
+      return QgsVectorLayerExporter::ErrCreateLayer;
+    }
+  }
 
   if ( !geometryColumn.isEmpty() )
   {

tests/src/python/test_provider_mssql.py

@@ -298,6 +298,25 @@ def testInsertPolygonInMultiPolygon(self):
         geom = [f.geometry().asWkt() for f in new_layer.getFeatures()]
         self.assertEqual(geom, ['MultiPolygon (((0 0, 1 0, 1 1, 0 1, 0 0)),((10 0, 11 0, 11 1, 10 1, 10 0)))', 'MultiPolygon (((30 0, 31 0, 31 1, 30 1, 30 0)))'])
 
+    def testOverwriteExisting(self):
+        layer = QgsVectorLayer("NoGeometry?field=pk:integer", "addfeat", "memory")
+        pr = layer.dataProvider()
+        f = QgsFeature()
+        f.setAttributes([133])
+        pr.addFeatures([f])
+
+        uri = '{} table="qgis_test"."sacrificalLamb" sql='.format(self.dbconn)
+        new_layer = QgsVectorLayer(uri, 'new', 'mssql')
+        self.assertTrue(new_layer.isValid())
+        self.assertEqual([f.attributes() for f in new_layer.getFeatures()], [[1]])
+
+        # try to overwrite
+        error, message = QgsVectorLayerExporter.exportLayer(layer, uri, 'mssql', QgsCoordinateReferenceSystem())
+        self.assertEqual(error, QgsVectorLayerExporter.ErrCreateLayer)
+
+        # should not have overwritten features
+        self.assertEqual([f.attributes() for f in new_layer.getFeatures()], [[1]])
+
     def testMultiGeomColumns(self):
         uri = '{} table="qgis_test"."multiGeomColumns" (geom1) sql='.format(self.dbconn)
         new_layer = QgsVectorLayer(uri, 'new', 'mssql')

tests/testdata/provider/testdata_mssql.sql

@@ -25,6 +25,9 @@ GO
 DROP TABLE IF EXISTS qgis_test.[multiGeomColumns];
 GO
 
+DROP TABLE IF EXISTS qgis_test.[sacrificalLamb];
+GO
+
 DROP SCHEMA qgis_test;
 GO
 
@@ -69,6 +72,11 @@ CREATE TABLE qgis_test.[multiGeomColumns] (
 );
 GO
 
+CREATE TABLE qgis_test.[sacrificalLamb] (
+    pk integer PRIMARY KEY
+);
+GO
+
 INSERT INTO qgis_test.[someData] (pk, cnt, name, name2, num_char, geom) VALUES
 (5, -200, NULL, 'NuLl', '5', geometry::STGeomFromText( 'Point(-71.123 78.23)', 4326 )),
 (3,  300, 'Pear', 'PEaR', '3', NULL),
@@ -93,6 +101,10 @@ INSERT INTO qgis_test.[float_dec] (id, float_field, dec_field ) VALUES
  (1, 1.1111111111, 1.123 );
 GO
 
+INSERT INTO qgis_test.[sacrificalLamb] (pk) VALUES
+ (1);
+GO
+
 INSERT INTO qgis_test.[multiGeomColumns] (pk, geom1, geom2) VALUES
 (5, geometry::STGeomFromText( 'Point( 1 2 )', 4326 ), NULL),
 (3, NULL, geometry::STGeomFromText( 'LineString( 1 2, 3 4 )', 4326 )),