Rails generalizing a method that uses models - ruby-on-rails

Question

I am trying to generalize few methods that will be used by multiple models/views/controllers but i'm having no luck. Here is the original code that works when it is just for 1 set called Trucks.
View
<h2>Trucks</h2>
<%= form_tag trucks_path, :method => 'get' do %>
<%= hidden_field_tag :direction, params[:direction] %>
<%= hidden_field_tag :sort, params[:sort] %>
<p>
Search:
<%= text_field_tag :search %>
by
<%= select_tag :search_column, options_for_select(Truck.translated_searchable_columns(['attribute1']), params[:search_column]) %>
<%= submit_tag "Search" %>
</p>
<% end %>
<!-- Display code goes here, but im not showing since its just a table -->
Controller
def index
#trucks = Truck.search(params[:search], params[:search_column]).order(sort_column(Truck, "truck_no") + " " + sort_direction)
respond_to do |format|
format.html # index.html.erb
format.json { render json: #trucks }
end
end
Model
class Truck < ActiveRecord::Base
attr_accessible :attribute1, :attribute2, :attribute3
def self.search(keyword, column_name)
if self.column_names.include?(column_name.to_s)
where("trucks.#{column_name} LIKE ?", "%#{keyword}%")
else
scoped
end
end
def self.searchable_columns(unwanted_columns)
self.column_names.reject{ |column| unwanted_columns.include?(column) }
end
def self.translated_searchable_columns(unwanted_columns)
columns = self.searchable_columns(unwanted_columns)
result = columns.map{ |column| [Truck.human_attribute_name(column.to_sym), column] }
result
end
end
All this works without a hitch, now I can't figure out for the life of me how to move these methods to lib and have them generalized so that lets say Trailers is able to call in the same method and pass in its information and achieve the same result. I am trying to make this code DRY as possible. Could anyone explain me what I need to do to achieve this? How does lib access the database?

Answer 1

The concept you're looking for is called a "concern". Rails has a convenience module for implementing concerns called ActiveSupport::Concern. Here's how you might extract your model methods:
module Searchable
extend ActiveSupport::Concern
module ClassMethods
def search(keyword, column_name)
if column_names.include?(column_name.to_s)
where("#{table_name}.#{column_name} LIKE ?", "%#{keyword}%")
else
scoped
end
end
def searchable_columns(unwanted_columns)
column_names.reject{ |column| unwanted_columns.include?(column) }
end
def translated_searchable_columns(unwanted_columns)
columns = searchable_columns(unwanted_columns)
columns.map{ |column| [human_attribute_name(column.to_sym), column] }
end
end
end
And then in your model:
class Truck < ActiveRecord::Base
include Searchable
attr_accessible :attribute1, :attribute2, :attribute3
end
As for where exactly you should store the Searchable module, it's up to you -- it just has to be someplace that's included in config.autoload_paths, just like a model or controller. Rails 4 introduced a convention that model concerns are stored in app/models/concerns, and controller concerns in app/controllers/concerns, but there is nothing special about these locations other than being autoloaded by default.