Currently there's no good way in EF Core to work with fields in Cosmos that can contain arbitrary JSON. We would love a way to both read and write to fields like that.

The Npgsql provider appears to have elegantly solved this by adding support for JsonDocument column types (ref: http://www.roji.org/efcore-pg-advanced-json#weakly-typed-access-via-jsondocument). Having matching functionality with the Cosmos provider would be exactly what we need.