[Qgis-developer] Improve server-side compiled expressions for PostGreSQL

[kimaidou]

Hi all,

I usually work with PostgreSQL data in QGIS.
I would like to have a guidance on how to improve the set of compiled
expressions for PostgreSQL. My goal is to propose a PR for some spatial
function.

I think the files are here
src/providers/postgres/qgspostgresexpressioncompiler.cpp
src/providers/postgres/qgspostgresfeatureiterator.cpp

For example, I would like the following expression to be compiled server
side:

    intersects(
        $geometry,
        geom_from_gml(
            '<gml:Polygon+xmlns:gml="http://www.opengis.net/gml
"><gml:outerBoundaryIs><gml:LinearRing><gml:coordinates+decimal="."+cs=","+ts="+">MY_GML_COORDINATES</gml:coordinates></gml:LinearRing></gml:outerBoundaryIs></gml:Polygon>'
        )
    )

where MY_GML_COORDINATES is the GML version of a polygon ring coords.

What are the required steps to do so, and where ? The result would be


    ST_Intersects(
        geom,
        ST_GeomFromGml( 'the long GML polygon representation')
    )

Regards,
Michaël
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