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