Associations

You can easily use Ransack to search for objects in has_many and belongs_to associations.

Given these associations...

class Employee < ActiveRecord::Base
  belongs_to :supervisor

  # has attributes first_name:string and last_name:string
end

class Department < ActiveRecord::Base
  has_many :supervisors

  # has attribute title:string
end

class Supervisor < ActiveRecord::Base
  belongs_to :department
  has_many :employees

  # has attribute last_name:string
end

... and a controller...

class SupervisorsController < ApplicationController
  def index
    @q = Supervisor.ransack(params[:q])
    @supervisors = @q.result.includes(:department, :employees)
  end
end

... you might set up your form like this...

<%= search_form_for @q do |f| %>
  <%= f.label :last_name_cont %>
  <%= f.search_field :last_name_cont %>

  <%= f.label :department_title_cont %>
  <%= f.search_field :department_title_cont %>

  <%= f.label :employees_first_name_or_employees_last_name_cont %>
  <%= f.search_field :employees_first_name_or_employees_last_name_cont %>

  <%= f.submit "search" %>
<% end %>
...
<%= content_tag :table do %>
  <%= content_tag :th, sort_link(@q, :last_name) %>
  <%= content_tag :th, sort_link(@q, :department_title) %>
  <%= content_tag :th, sort_link(@q, :employees_last_name) %>
<% end %>

If you have trouble sorting on associations, try using an SQL string with the pluralized table ('departments.title','employees.last_name') instead of the symbolized association (:department_title), :employees_last_name).

Associations​

Associations