Overriding a module method from a gem in Rails

A more concise solution:

WillPaginate::Finder::ClassMethods.module_eval do def paginate_by_sql sql, options   # Your code here endend

Put the the code into an initializer file in config/initializers. This is the correct place to put code that needs to be run when the environment is loaded. It also better organises your code, making each file's intent clearer, thus bugs will be easier to track down. Do not clutter up environment.rb!

Ok, I'm just going to make this easier for people like myself who come along and still struggle a bit after reading the other answers.

First find the code that you want to change on the github repo by searching for the line of code (you could easily find this using pry) you want to change in the gem, and then selecting Code on the left instead of Issues

Next Copy the content of the module you want to change and place it into an aptly named .rb file inside of your config/initializers folder. Here is an example:

module Forem  module TopicsHelper    def link_to_latest_post(post)      text = "#{time_ago_in_words(post.created_at)} #{t("ago_by")} #{post.user}"      link_to text, forum_topic_path(post.topic.forum, post.topic, :anchor => "post-#{post.id}")    end  endend

Now, change it to:

Forem::TopicsHelper.module_eval do  def link_to_latest_post(post)    text = "#{time_ago_in_words(post.created_at)} #{t("ago_by")} #{post.user}"    link_to text, forum_topic_path(post.topic.forum, post.topic, :anchor => "post-#{post.id}")  endend

Now, make any additional changes to the code and restart your server.

Away you go!

What you are doing will work, but your code needs to look like this:

module WillPaginate  module Finder    module ClassMethods      def paginate_by_sql(sql, options)        # your code here      end    end  endend

In other words, go into finder.rb, delete everything except the module headers and the method you want to override, then save to a file in lib and include in environment.rb. Voila, instant monkey patch!