Validation error status code¶

Changing FastAPI's default 422 for request validation errors is not something RouterVersioner does itself: it's a separate, general-purpose concern, handled by the fastapi-validation-override package. openapi_hook is the integration point: it lets you re-apply the same patch to every per-version schema that RouterVersioner generates, so all of them, root schema included, stay consistent.

uv add fastapi-validation-override

from fastapi_validation_override import (
    override_validation_error,
    patch_422_responses,
)

# 1. Registers the runtime handler and patches the app's own root /openapi.json.
override_validation_error(app, status_code=400)

# 2. Re-applies the same patch to each version's own schema.
def versioning_openapi_hook(schema: dict, version: tuple[int, int]) -> dict:
    return patch_422_responses(schema, "400")

RouterVersioner(
    app=app,
    routers=router,
    version_format=VersionFormat.SEMVER,
    openapi_hook=versioning_openapi_hook,
).versionize()
# Validation failures now return 400, both at runtime and in every schema
# (root, and every /vX_Y/openapi.json)

See examples/validation_override_integration_app.py.