Write a custom Aggregate for AsMVT

[submarcos]

• see django Aggregate class
• see django Subquery class

-> Feature.objects.filter(xxx).annotate(geom_prepared=AsMVTGeom('geom', xxx)).aggregate(tile=AsMVT(xxx))

-> Layer.objects.values('name').aggregate(tile=AsMVT(Feature.objects.annotate(geom_prepared=AsMVTGeom('geom', xxx)).filter(layer_id=OuterRef('pk')), xxx))

[StefanBrand]

Stackoverflow has a question on this here: https://stackoverflow.com/questions/65508291/how-to-create-mapbox-vector-tiles-with-django-orm-and-postgis

[submarcos]

It's possible to write a custom aggregate, but

• by default django use a subquery, and if we pass ST_ASMVT((geom, some_field), extent, xxx), ST_ASMVT generate tile with automatic field name for properties (don't keep alias or column names) ST_ASMVT bug ? (properties are named f1, f2 etc)
• if we use ST_ASMVT(subquery.*, extent, xxx), it's ok, ST_ASMVT keep alias for column names, but... django ORM rename column on joins, so ... properties are named col1, col2 etc ...

It seems not to be simple to resolve that, because aggregation and column rename are define in SQLAggregate Compiler which can't be override