1. Introduction

In this tutorial, we will focus on handling and logging errors in Rails. Error handling is a crucial part of any application. It ensures that the application can gracefully handle unexpected events and provide useful feedback to the user. Additionally, logging errors is equally important as it aids in the debugging process and helps in monitoring the system for issues.

By the end of this tutorial, you will:

• Understand how to handle errors and exceptions in Rails.
• Learn how to log errors for further analysis.
• Implement best practices for error handling and logging.

Prerequisites

To follow this tutorial, you should have:

• Basic knowledge of Ruby and Rails.
• A development environment with Ruby and Rails installed.

2. Step-by-Step Guide

Error Handling in Rails

In Rails, errors are handled using exceptions. When an error occurs, an exception is raised. If not caught and handled, this exception will propagate up the stack causing the program to halt.

To handle exceptions, Rails provides the rescue_from method. This method can be used in controllers to specify how to rescue from a specific exception.

Logging in Rails

Rails uses the logger method for logging. By default, Rails logs all requests and responses in the log file located in log/ directory of your application.

3. Code Examples

Example 1: Handling a RecordNotFound error

class ApplicationController < ActionController::Base
  rescue_from ActiveRecord::RecordNotFound, with: :record_not_found

  private

  def record_not_found
    render plain: "404 Not Found", status: 404
  end
end

In this example:

• We use the rescue_from method in the ApplicationController.
• The rescue_from method takes two arguments: the exception class and a symbol representing the method to be called when this exception occurs.
• When a RecordNotFound error occurs in any controller inheriting from ApplicationController, the record_not_found method is called. This method renders a plain "404 Not Found" message with a status code of 404.

Example 2: Logging an error

class ApplicationController < ActionController::Base
  rescue_from StandardError, with: :handle_error

  private

  def handle_error(e)
    logger.error e.message
    render plain: "500 Internal Server Error", status: 500
  end
end

In this example:

• We rescue from StandardError, which is the base class for most error types.
• In the handle_error method, we log the error message using logger.error and render a "500 Internal Server Error" response.

4. Summary

In this tutorial, you have learned how to handle and log errors in Rails. You've seen how to use the rescue_from method to catch and handle exceptions, and how to use the logger method to log errors.

To further your learning, try to:

• Explore other methods provided by the logger object.
• Learn about different types of exceptions in Rails and how to handle them.
• Look into more advanced logging options, such as logging to an external service.

5. Practice Exercises

1. Create a Rails application and generate a few errors. Use the rescue_from method to handle these errors.

2. Implement a custom logger that logs errors in a different format or to a different location.

3. Create a middleware that catches and logs all exceptions before they reach your controllers.

Remember, the key to mastering error handling and logging is practice. Don't be afraid to experiment with different techniques and tools. Good luck!