Adding custom code (Ruby) | Fern Documentation

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These pages cover SDK generation configured with generators.yml. New projects use sdk-config.yml, so see the Current version of this page for up-to-date guidance. To move an existing project, follow the SDK Config migration guide, which walks through fern sdk migrate, and review the sdk-config.yml reference.

Enterprise feature

This feature is available only for the Enterprise plan. To get started, reach out to support@buildwithfern.com.

This page covers how to add custom logic, methods, and dependencies to your Ruby SDK.

Adding custom logic

To get started adding custom code:

These steps cover adding a new custom file to the SDK. To preserve line-level edits to a generated file, use Replay instead.

Create a new file and add your custom logic

lib/<gem_name>/helper.rb

module YourGem
  class Helper
    def self.my_helper
      puts "Hello World!"
    end
  end
end

Add your file to `.fernignore`

.fernignore

# Specify files that shouldn't be modified by Fern
lib/<gem_name>/helper.rb

Consume the helper

Now your users can consume the helper function by importing it from the SDK.

require "your_gem"
YourGem::Helper.my_helper

Adding custom SDK methods

Fern also allows you to add custom methods to the SDK itself (e.g. client.my_method() ) by inheriting the Fern generated client and then extending it.

Update `generators.yml` configuration

Name your Fern-generated client something like BaseClient to reflect that this client will be extended.

generators.yml

- name: fern-ruby-sdk
  version: 1.39.2
  config:
    clientClassName: BaseClient

Import and extend the generated client

First, import the Fern generated base client and extend it. Then, add whatever methods you want.

lib/<gem_name>/my_client.rb

require_relative "client"
module YourGem
  class MyClient < BaseClient
    def my_helper
      puts "Hello World!"
    end
  end
end

Update `.fernignore`

Add the my_client.rb to .fernignore.

.fernignore

+ lib/<gem_name>/my_client.rb

Consume the method

Instead of constructing the generated client, your users will want to construct the extended client.

require "your_gem"
client = YourGem::MyClient.new

Now your users can consume the helper function by importing it from the SDK.

client.my_helper

Adding custom dependencies

To add gems that your custom code requires, update your generators.yml.