[Qgis-developer] GDAL 2.1 can update Geojson files - What is missing in QGIS to edit GeoJSON files ?

[Even Rouault]

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

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