[OGR] Ensure subset string is set when reopening dataset

QgsOgrProvider::reloadData calls close() and open(), which in turn called setSubsetString with mSubsetString.
Since setSubsetString does nothing if the passed sql string is equal to mSubsetString, this resulted in the
substring not being set on re-open. This commit clears mSubsetString before calling setSubsetString, and
blocks signals when calling setSubsetString to avoid an endless recursion of emit dataChanged -> reload.
Fixes #17122.

src/providers/ogr/qgsogrprovider.cpp

@@ -3574,7 +3574,13 @@ void QgsOgrProvider::open( OpenMode mode )
       // check that the initial encoding setting is fit for this layer
       setEncoding( encoding() );
 
-      mValid = setSubsetString( mSubsetString );
+      // Ensure subset is set (setSubsetString does nothing if the passed sql subset string is equal to mSubsetString, which is the case when reloading the dataset)
+      QString origSubsetString = mSubsetString;
+      mSubsetString = "";
+      // Block signals to avoid endless recusion reloadData -> emit dataChanged -> reloadData
+      blockSignals( true );
+      mValid = setSubsetString( origSubsetString );
+      blockSignals( false );
       if ( mValid )
       {
         if ( mode == OpenModeInitial )

tests/src/python/test_provider_ogr_sqlite.py

@@ -130,7 +130,10 @@ def testFidSupport(self):
         self.assertEqual(got, [(12, 123)])
 
     def testSubsetStringFids(self):
-        """ tests that feature ids are stable even if a subset string is set """
+        """
+          - tests that feature ids are stable even if a subset string is set
+          - tests that the subset string is correctly set on the ogr layer event when reloading the data source (issue #17122)
+        """
 
         tmpfile = os.path.join(self.basetestpath, 'subsetStringFids.sqlite')
         ds = ogr.GetDriverByName('SQLite').CreateDataSource(tmpfile)
@@ -172,6 +175,7 @@ def testSubsetStringFids(self):
 
         vl = QgsVectorLayer(tmpfile + "|subset=type=2", 'test', 'ogr')
         self.assertTrue(vl.isValid())
+        self.assertTrue(vl.fields().at(0).name() == "orig_ogc_fid")
 
         req = QgsFeatureRequest()
         req.setFilterExpression("value=16")
@@ -180,6 +184,10 @@ def testSubsetStringFids(self):
         self.assertTrue(it.nextFeature(f))
         self.assertTrue(f.id() == 5)
 
+        # Check that subset string is correctly set on reload
+        vl.reload()
+        self.assertTrue(vl.fields().at(0).name() == "orig_ogc_fid")
+
 
 if __name__ == '__main__':
     unittest.main()