1 Overview

Whenever we have an application error, we want to respond with a JSONAPI-compliant errors payload. This way clients have a predictable response detailing information about the error.

We’ll also need a way to customize this payload. For instance, if a NotAuthorized error is raised, the response should have a 403 status code. For other errors, we may want to render a helpful error message:

class ApplicationController < ActionController::API
  register_exception NotAuthorized, status: 403
  register_exception ShipmentDelayed,
    message: ->(e) { "Contact us at 123-456-7899" }
  # ... code ...
end

Correctly handling exceptions happens in graphiti-rails. Customizing the behavior based on error class happens in the RescueRegistry dependency.

1.1 Setup

Just make sure you have graphiti-rails installed:

gem 'graphiti-rails'

And you’re all set!

1.1.1 Displaying Raw Errors


It can be useful to display the raw error as part of the JSON response - but you probably don’t want to expose your stack trace to customers. Let’s only show raw errors for the staging environment:

class ApplicationController < ActionController::API
  # ... code ...

  def show_detailed_exceptions?
    Rails.env.staging?
  end
end

Another common pattern is to only show raw errors when the user is privileged to see them:

class ApplicationController < ActionController::API
  # ... code ...

  def show_detailed_exceptions?
    Rails.env.staging?
  end
end

When #show_detailed_exceptions? returns true, you’ll get the raw error class, message, and backtrace in the JSON response.

2 Usage

2.1 Basic

Let’s register an error with a custom response code:

register_exception Errors::NotAuthorized, status: 403

Now if we raise Errors::NotAuthorized, the response code will be 403.

Additional options:

register_exception Errors::NotAuthorized,
  status: 403,
  title: "You cannot perform this action",
  message: true, # render the raw error message
  message: ->(error) { "Invalid Action" } # message via proc

See full documentation in the RescueRegistry README.

All controllers will inherit any registered exceptions from their parent. They can also add their own. In this example, FooError will only throw a custom status code when thrown from FooController:

class FooController < ApplicationController
  register_exception FooError, status: 422
end

2.2 Advanced

The final option register_exception accepts is handler. Here you can inject your own error handling class that customize RescueRegistry::ExceptionHandler. For example:

class MyCustomHandler < GraphitiErrors::ExceptionHandler
  # self.exception accessible within all instance methods

  def status_code
    # ...customize...
  end

  def error_code
    # ...customize...
  end

  def title
    # ...customize...
  end

  def detail
    # ...customize...
  end

  def meta
    # ...customize...
  end
end

register_exception FooError, handler: MyCustomHandler

If you would like to use the same custom handler for all errors, override default_exception_handler:

# app/controllers/application_controller.rb
def self.default_exception_handler
  MyCustomHandler
end

3 Testing

This pattern of globally rescuing exceptions makes sense when running our live application…but during testing, we may want to raise real errors and bypass this rescue logic.

This is why we turn off error-handling during tests by default:

# spec/rails_helper.rb
RSpec.configure do |config|
  config.include Graphiti::Rails::TestHelpers
  # ... code ...

  config.before :each do
    handle_request_exceptions(false)
  end
end

If you want to turn this on for an individual test (so you can test error codes, etc):

before do
  handle_request_exceptions(true)
end