Rails Error Handling

Validation Errors

• Use errors.add(:field, "message") to attach custom messages in validations
• Use errors.full_messages for user display; errors.details for API/machine-readable output
• Prefer ActiveModel::Validator or validate :method_name over inline logic
• Always write clear, user-friendly validation messages

Exceptions & Rescue

• Never rescue generic StandardError unless you re-raise it
• Use rescue_from in ApplicationController for domain-specific errors (e.g., ActiveRecord::RecordNotFound)
• Raise custom exceptions as subclasses of StandardError; include context and error codes
• Custom error hierarchy: ApplicationError < StandardError, then AuthenticationError, AuthorizationError, ValidationError, ExternalServiceError
• Avoid silent failures — always log unexpected exceptions with context
• Set the correct HTTP status code whenever you render an error response

Custom Error Pages