GlobalSecondaryIndex + Polymorphism

[ynie]

Hey all, I'm new to pynamoDB. Here is my setup

class DateIndex(GlobalSecondaryIndex):
    class Meta:
        projection = AllProjection()
    data_type = UnicodeAttribute(hash_key=True)

class CredentialBase(Model):
    id = UnicodeAttribute(hash_key=True)
    date_index = DataTypeDateIndex()
    cls = DiscriminatorAttribute()

class Credential(CredentialBase, discriminator='Credential"):
    class Meta:
        table_name = ""

Why wouldn't this work?
results = Credential.date_index.query("", limit=1)

It tries to look up the dateIndex on CredentialBase instead of Credential. I can fix the problem by moving the date_index to the childClass Credential. Is that the correct way of doing it? Thanks!