Throw a user-facing error

When running functions in other parts of the platform, such as Workshop or Actions, you may want to throw an error with a detailed message. To do so, throw a UserFacingError from the functions.api module. For example:

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from functions.api import function, UserFacingError
from ontology_sdk import FoundryClient
from ontology_sdk.ontology.object_sets import AircraftObjectSet
from ontology_sdk.ontology.objects import Aircraft


@function(edits=[Aircraft])
def edit_exactly_five_aircraft(
    aircraft_object_set: AircraftObjectSet
) -> list[OntologyEdit]:
    aircraft = list(aircraft_object_set)
    if not len(aircraft) == 5:
        raise UserFacingError(f"Pass in exactly 5 aircraft. Received ${len(aircraft)}.")
    ... # edit the objects

When running this as a Function-backed Action in a Workshop application with an incorrect number of employees, users will see the following error:

By adding a detailed user facing error message, you can help other users of your Function quickly identify and fix the issue.