Module migrations

Oftentimes you start depending on new types in-between versions. For example, let's say that you depended on Invoice schema within your data.head.users in older versions but now you do not. This means that once we run code generation and this type gets back into some annotation of some schema in data.head.users -- it will not be imported because it was not imported in latest. To solve problems like this one, we have module instructions:

from cadwyn.structure import VersionChange, module
import data.head.users


class MyChange(VersionChange):
    description = "..."
    instructions_to_migrate_to_previous_version = (
        module(data.head.users).had(import_="from .invoices import Invoice"),
    )

Which will add-in this import at the top of users file in all versions before this version change.