Polymorphic schema usage

Hi, I have a question regarding usage of polymorphic schema objects.

Say, I have a base Config class object, with only id, name and type fields:

class Config(Schema):
    id = base_fields.Integer(description='Configuration ID', required=True)
    name = base_fields.String(description='Configuration name', required=True)
    type = base_fields.Integer(description='Configuration type', required=True)

Now, assuming that there will be many schema types that derives from Config but each with specific field(s), like:

class ConfigFile(Schema):
    path = base_fields.String(description='Config file path', required=True)

class ConfigDB(Schema):
    user = base_fields.String(description='DB username', required=True)
    password = base_fields.String(description='DB password', required=True)

When e.g. I pull data from the DB, I will get list of SQLAlchemy objects that are polymorphic, and type is a discriminator:

__mapper_args__ = {'polymorphic_identity': 'ConfigFile'} 
...
__mapper_args__ = {'polymorphic_identity': 'ConfigDB'} 

Is it possible to use ConfigFile schema when for example, creating a response which can hold list of objects that are sub-classes of it like:

class ConfigResponse(Schema):
    response = base_fields.Nested(ConfigFile, description='', many=True, required=True)

Is usage of marshmallow-oneofschema safe or some custom fix is recommended? Additional reason to ask is because we also use flasgger and I am not sure how it will ‘dance’ with it.

One additional question, not related to this topic: what are performance penalties comparing to usage of custom serialize method/class based on plain dictionaries? I like the library, but one of my coworkers keeps undermine usage of it based on suspicions regarding speed and not only that but also of ease of usage. I think second can not be further from the truth, but for speed I am not sure how much is the overhead. Are there some figures already, or to make my own test?

Thank you in advance

[deckar01]

https://swagger.io/docs/specification/data-models/inheritance-and-polymorphism/

Apispec uses a “discriminator” to solve the problem of determining which schema an object belongs to. It’s not a perfect solution, but I think it is something that marshmallow/apispec could implement.

[nikoladsp]

Thank you all!