Errors

---

Resolvers can raise errors in the course of executing, and handle errors in resolving other feature values.

---

​

Raising errors

If your resolver fails by raising an exception, the error will be surfaced as a ChalkError in query responses. Clients will receive a null value for the feature, and by default, downstream resolvers won’t run.

---

​

Handling errors

By default, if there was an error in computing one of the inputs to a resolver, that resolver will also fail with the error code UPSTREAM_FAILED. To handle failures in the input features, take as input the feature value, but wrapped in typing.Optional:

from typing import Optional

@online
def fn(score: Optional[User.fraud_score]) -> ...:

The argument score will receive the value None in the case of a failure.

If you’d like to provide a default value to use in the case of a failure, you can use Python’s syntax for assigning a default value to an argument:

@online
def fn(score: Optional[User.fraud_score] = -1) -> ...: