ActiveStorage declares several non-schema models, used purely for encapsulating business logic and operating on other (data-derived) models. Most of these (e.g. ActiveStorage::Current, ActiveStorage::Filename, ActiveStorage::Variant, and ActiveStorage::Variation) are database-agnostic and will suffice as-is. Some will require closer consideration.

1. ActiveStorage::Preview is mostly database-agnostic but does invoke ActiveRecord::Base.connected_to at one point in order to direct subsequent queries to an appropriate writable database.
2. ActiveStorage::VariantWithRecord is also mostly database-agnostic but also invokes ActiveRecord::Base.connected_to at one point.
3. ActiveStorage::Blob::Representable has several hooks that invoke background jobs (see “ActiveStorage Background Jobs,” below) as well as association and lifecycle declarations that are added when the concern is included. It may not be possible to incrementally modify this concern; in the worst case, we will simply copy it and make the necessary changes in the copy.