Summary

Pydantic provides Field(json_schema_extra=...) which allows to do something like:

def forbid_internal_labels(value):
    if re.match(r"^reserved-for-internal-use:.*$", value):
        raise ValueError(...)

class Foo(BaseModel):
    label: Annotated[str, AfterValidator(forbid_internal_labels), Field(json_schema_extra={
        "not": {
            {
                "type": "string",
                "pattern": "^reserved-for-internal-use:.*$"
            },
        }
    })]

This would generate:

                "type": "string",
                "not": {
                    {
                        "type": "string",
                        "pattern": "^reserved-for-internal-use:.*$"
                    },
                }

It doesn't actually add/do any validation, it merely impacts the generated JSON schema.

Similar mechanism is needed for Parameter, to inject discriminators (e.g. anyOf, not) into the OpenAPI spec (although the validation is decoupled from the schema declaration).

The builtin generation uses oneOf for union types (IIRC Pydantic uses anyOf for those). But I don't think it's possible to declare something like above.

Workarounds at this point would be:

• To adjust via custom Operation class (did not try but I assume it could work)
• To adjust the OpenAPI generation on a more global level (by extending OpenAPIPlugin?)

Both are quite ugly hacks, while something like this should be supported out-of-the-box.

Basic Example

No response

Drawbacks and Impact

No response

Unresolved questions

No response