company.rb

# Denormalized multi-valued indexing with Solr and Sunspot

class Company
  has_many :services
  has_many :products

  searchable do
    text :name
    text :description
    string :service_names, :multiple => true
    string :product_names, :multiple => true
  end

  def service_names
    services.collect(&:name)
  end

  def product_names
    products.collect(&:name)
  end

  # this record will be indexed a lot - best to queue it with DJ
  handle_asynchronously :solr_index
end

class Product
  has_and_belongs_to_many :companies # or a has_many :through, or a belongs_to, whatever...
  after_create :update_companies # or update_company, if a belongs_to...

  def update_companies
    companies.map(&:solr_index)
  end
end

class Service
  has_and_belongs_to_many :companies # or a has_many :through, or a belongs_to, whatever...
  after_create :update_companies # or update_company, if a belongs_to...

  def update_companies
    companies.map(&:solr_index)
  end
end

controller.rb

class CompaniesController < ApplicationController

  def search
    @search = Company.search do
      keywords params[:q]
      with(:service_names, params[:service_names]) # e.g., ["testing", "marketing", "plumbing", ...]
      with(:product_names, params[:product_names])
    end
    @companies = Search.results
  end

  # ...

end