MongoDB currently only supports the Draft-04 JSON Schema standard (with some omissions) for validation purposes. Draft-04 is pretty long in the tooth now.

Please enhance JSON Schema validation to support the latest 2019-09 Draft of the standard, specifically including the ability to do conditional subschema validation (ie. if/then/else  keyword support), which can be found here: https://json-schema.org/specification.html

Mongoose provides good support for discriminators, where the structure of a document/subdocument depends on a type field (typically _type), as does Mongoid for subclasses.

Validation of collections that use discriminators is not really possible without support for the if/then/else JSON Schema specification laid out  in the most recent draft of the standard.