Error Handling
When using dry-operation, errors are handled through the Failure type from dry-monads. Each step in your operation should return either a Success or Failure result. When a step returns a Failure, the operation short-circuits, skipping the remaining steps and returning the failure immediately.
You'll usually handle the failure from the call site, where you can pattern match on the result to handle success and failure cases. However, sometimes it's useful to encapsulate some error handling logic within the operation itself.
Global error handling
You can define a global failure handler by implementing an #on_failure method in your operation class. This method is only called to perform desired side effects and it won't affect the operation's return value.
class CreateUser < Dry::Operation
def initialize(logger:)
@logger = logger
end
def call(input)
attrs = step validate(input)
user = step persist(attrs)
step notify(user)
user
end
private
def on_failure(failure)
# Log or handle the failure globally
logger.error("Operation failed: #{failure}")
end
end
The #on_failure method can optionally accept a second argument that indicates which method encountered the failure, allowing you more granular control over error handling:
class CreateUser < Dry::Operation
def initialize(logger:)
@logger = logger
end
def call(input)
attrs = step validate(input)
user = step persist(attrs)
step notify(user)
user
end
private
def on_failure(failure, step_name)
case step_name
when :validate
logger.error("Validation failed: #{failure}")
when :persist
logger.error("Persistence failed: #{failure}")
when :notify
logger.error("Notification failed: #{failure}")
end
end
end