mongoengine_referencing_documents.py

from mongoengine import Document, EmbeddedDocument, Q, ReferenceField
from pymongo.read_preferences import ReadPreference

all_models = Document.__subclasses__()

def referencing_models(document):
   for model in all_models:
      if issubclass(model, EmbeddedDocument):
         continue
      fields = [field for field in get_reference_fields_of_model(model)
                if field.document_type == type(document)]
      if fields:
         yield (model, fields)

def get_referencing_documents(document):
   for model, fields in referencing_models(document):
      query = None
      for field in fields:
         params = {field.name: document.id}
         subquery = Q(**params)
         if query:
            query |= subquery
         else:
            query = subquery

      objects = (model
        .objects(subquery, read_preference=ReadPreference.SECONDARY_ONLY)
        .no_dereference()
        .no_cache())

      for ref_doc in objects:
         yield ref_doc