Change a schema that is not used in any endpoint

In some situations, you may want to use versioning not only for your OpenAPI schemas and endpoints but also within your code, for example to send versioned webhooks to your clients.

Suppose you want to change the type of an id field from integer to string:

from pydantic import BaseModel

from cadwyn import (
    ResponseInfo,
    VersionChange,
    convert_response_to_previous_version_for,
    schema,
)


# User from latest version
class User(BaseModel):
    id: str


class ChangeUserIDToString(VersionChange):
    description = (
        "Change users' ID field to a string to support any kind of ID. "
        "Be careful: if you use a non-integer ID in a new version and "
        "try to get it from the old version, the ID will be zero in response"
    )
    instructions_to_migrate_to_previous_version = [
        schema(User).field("id").had(type=int),
    ]

    @convert_response_to_previous_version_for(User)
    def change_id_to_int(response: ResponseInfo): ...

Unless there is an endpoint that has User as its response_model, this code will end up causing an error when you run the Cadwyn app. This is because Cadwyn tries to make sure that all of your converters apply to at least one endpoint. Otherwise, it would be too easy for you to make a mistake when writing converters for the wrong schemas.

To avoid it, set check_usage=False:

from pydantic import BaseModel

from cadwyn import (
    ResponseInfo,
    VersionChange,
    convert_response_to_previous_version_for,
    schema,
)


# User from latest version
class User(BaseModel):
    id: str


class ChangeUserIDToString(VersionChange):
    description = (
        "Change users' ID field to a string to support any kind of ID. "
        "Be careful: if you use a non-integer ID in a new version and "
        "try to get it from the old version, the ID will be zero in response"
    )
    instructions_to_migrate_to_previous_version = [
        schema(User).field("id").had(type=int),
    ]

    @convert_response_to_previous_version_for(User, check_usage=False)
    def change_id_to_int(response: ResponseInfo): ...