Digital illustration highlighting custom error handling in Ruby on Rails. It showcases a computer screen with Ruby code defining ‘class CustomError < StandardError’, surrounded by warning icons and alert symbols. The Ruby on Rails logo is subtly integrated in the background, emphasizing the framework’s adaptability in error management.
Mastering Custom Error Handling in Ruby on Rails: Coding Precision and Flexibility

Mastering Custom Errors in Rails

Alessio Bussolari
2 min readNov 27, 2023

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Ruby on Rails, known for its convention over configuration approach, also provides great flexibility in handling exceptions and errors. Implementing custom errors in a Rails application can greatly improve code readability, error management, and user experience. In this article, we’ll explore the reasons for using custom errors and how to effectively implement them in a Rails app.

Why Implement Custom Errors?

  1. Clarity and Specificity: Custom errors allow you to define specific error types related to your domain logic, making your code more descriptive and understandable.
  2. Controlled Error Handling: They enable centralized handling of specific error cases, allowing for a more structured approach to error management.
  3. Improved User Experience: Custom errors can be tailored to provide more meaningful messages to the end user, improving overall user interaction.
  4. Ease of Debugging: Specific error types make it easier to pinpoint the source of an issue during debugging.

How to Implement Custom Errors in Rails

Step 1: Define Custom Error Classes

Create custom error classes in your application. It’s a good practice to define these in a dedicated directory, like app/errors.

# app/errors/invalid_order_error.rb
class InvalidOrderError < StandardError
def message
"The order could not be processed due to invalid data."
end
end

Step 2: Raise Custom Errors

Use these custom errors in your business logic where appropriate.

class OrderProcessor
def process(order)
raise InvalidOrderError unless order.valid?

# Processing logic here
end
end

Step 3: Rescue Custom Errors

Handle these errors at an appropriate level, such as in your application controller, background jobs, or service objects.

class ApplicationController < ActionController::Base
rescue_from InvalidOrderError do |exception|
render json: { error: exception.message }, status: :unprocessable_entity
end
end

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Alessio Bussolari

Ruby on Rails programmer since 2009. Current CTO at COSMIC SRL, where I lead the team in creating innovative solutions.