categories dropdown for product search

Question

I am having many products with many categories which are associated with has_many using memberships.

I am trying to create a search box where any one can search products while also filter their search with a category dropdown (so only products with relevant categories can be retrieved).

The thinking_sphinx index is in Product model I don't get any errors but dropdown does not effect the search.

MODEL: 
    has_many :memberships,:dependent=> :destroy
    has_many :categories, :through => :memberships
    named_scope :published, :conditions => {:publish => 1}
    define_index do
        indexes product_name
        indexes product_description
        indexes publish
        indexes memberships.product_id
        indexes memberships.category_id
        indexes categories.category_name
      end
    end

CONTROLLER: 
     @products = Product.search params[:search],:conditions=>{@product.memberships.category_id =>params[:category_product] },:page=> params[:page] || 1,:per_page =>4


VIEW:
           form_tag search_path, :method =>:get do 
           text_field_tag :search, params[:search]
           form_tag categories_path, :method => :get do 
           select_tag"category", options_from_collection_for_select (Category.find (:all,   :group=>:id), :id, :category_name,params[:category_product]) 
           end 
           submit_tag "search", :name => nil 
           end 

Answer 1

You need to use an attribute for filtering. In your define_index use a 'has' method, and in the search use a :with params. Something like :

define_index do
  …
  has categories(:id), :as => categories_id
  …
end

and the search would be :

Product.search params[:search], :with => { :categories_id => params[:category] }