OGRSQLiteDataSource::SaveStatistics does not call UpdateLayerStatistics for Spatialite 4 Db's

[mj10777]

In the Geopaparazzi forum it has been reported that spatialite 4 Databases created in QGIS with the 'Save as' function as 'Spatialite [OGR]' does not update the 'vector_layers_statistics' TABLE correctly.

​https://groups.google.com/forum/#!topic/geopaparazzi-users/DeJzGqg26NU

---

This function (in QGIS) is delt with in 'QgsVectorFileWriter::writeAsVectorFormat'

OGR runs OGRSQLiteTableLayer::RunDeferredCreationIfNecessary is called

• when the first feature is added (in QgsVectorFileWriter::writeFeature)
  • the TABLE will be created
  • UpdateLayerStatistics is called on the empty table

When all the features have been added

• OGR calls OGRSQLiteDataSource::SaveStatistics()
  • for each layer SaveStatistics() is called
    • which does nothing since HasSpatialite4Layout() is TRUE and returns -1

At this point an UpdateLayerStatistics is needed, since the table is now filled

• vector_layers_statistics.row_count remains 0 and the extent values NULL

---

I attempted a to workout a solution for this:

• in OGRSQLiteDataSource::SaveStatistics()

    if( hDB && nSavedAllLayersCacheData == TRUE )
    { // mj10777: allways FALSE for HasSpatialite4Layout()
      ...
    }
    else
    {
      if (HasSpatialite4Layout())
      {
        char* pszErrMsg = NULL;
        int rc = SQLITE_OK;
        rc = sqlite3_exec( hDB, "SELECT UpdateLayerStatistics()", NULL, NULL, &pszErrMsg );
        if( rc != SQLITE_OK )
        {
            CPLError( CE_Failure, CPLE_AppDefined,
                  "Unable to call %s: %s",
                  "UpdateLayerStatistics()", pszErrMsg );
            sqlite3_free( pszErrMsg );
        }
      }
    }

But although 'UpdateLayerStatistics()' is correctly called

• the vector_layers_statistics entry remains unchanged
  • cause unknown

---

Geopaparazzi will check if vector_layers_statistics.row_count is NULL

• and call 'UpdateLayerStatistics()' to repair it
  • but when row_count == 0, it is considered empty and thus not loaded

[Even Rouault]

In 37715:

SQLite: update layer statistics for Spatialite 4 DB (fixes #6838)