Le jeudi 14 janvier 2016 18:04:00, Matthias Kuhn a écrit : > On 01/14/2016 05:42 PM, Even Rouault wrote: > >> It will benefit from expression compiling (for filtering and order by) > >> which results in performance improvements when it can be applied. > > > > I'm not completely sure to know what you refer to in the QGIS context but > > the OGR SetAttributeFilter() method is directly evaluated by the SQLite > > request engine as a WHERE clause, and similarly for the ExecuteSQL() > > API. > > It tries to compile QgsExpressions to native SQL syntax. > > I think the point of using OGR that it offers an awesome abstraction > layer where the consumer doesn't need to care about the backend. > > As soon as ExecuteSQL is used this abstraction no longer applies and it > just adds another layer of uncertainty (different library versions...) > and may potentially hide internals of the backends which may be useful > in some cases (datatypes, backend metadata, available indexes, ...), so > the advantage is gone while it complicates advanced topics. > Or did I miss something?
- datatypes: all the ones listed in "Table 1. GeoPackage Data Types" http://www.geopackage.org/spec/#_sqlite_container have an OGR equivalent - backend metadata: not sure what you're thinking exactly too. But at some point this has to be translated in the QGIS abstraction too, no ? - available indexes: not present in the OGR abstraction currently (but the abstraction can be extended if needed, as it has been done in the past). Is QGIS aware of which indices exist ? A possibility would be to have a thin GeoPackage provider (I guess it could probably even by generic to most OGR drivers that have native SQL92 capabilities) extending the base OGR one + using its capabilities with the specificities of GPKG (eg adding the SORT BY clause). Or a more quick&dirty way would be to hack that directly in the OGR provider for the vetted OGR drivers. > > >>>> All the best -- Spatialys - Geospatial professional services http://www.spatialys.com _______________________________________________ Qgis-developer mailing list Qgis-developer@lists.osgeo.org List info: http://lists.osgeo.org/mailman/listinfo/qgis-developer Unsubscribe: http://lists.osgeo.org/mailman/listinfo/qgis-developer