class MyDocument(motorodm.Document):
     plain = motorodm.StringField()
     upper_case = motorodm.StringField(regex=re.compile('^[A-Z]*$'))
 class Person(motorodm.Document):
     name = motorodm.StringField(required=True, unique=True)
     parent = motorodm.ReferenceField(reference_document_type=lambda: Person)
 class Address(motorodm.Document):
     city = motorodm.StringField()
 class Person(motorodm.Document):
     name = motorodm.StringField()
     address = motorodm.ReferenceField(reference_document_type=Address)
 class DocA(motorodm.Document):
     foo = motorodm.StringField()
     pass