WORKING CODE: Reverse Jquery TokenInput ( How to get a many-many association working on the form when using the "authorships" form instead)

_form.html.erb

<%= form_for(@user_product) do |f| %>
    # This line is the virtual attribute base on a product_id and then the "data-pre" maps to my ProductsController/Application.js for the /products.json route.
    # Its for seeing the Product on the Edit form, it has to be found.
    <%= f.text_field :product_token, "data-pre" => @products.map(&:attributes).to_json %>
    <%= f.label :price %><br />
    <%= f.text_field :price %>
    <%= f.submit %>
<% end %>

application.js

$(function() {
  $("#user_product_product_token").tokenInput("/products.json", {
    prePopulate: $("#user_product_product_token").data("pre"),
    tokenLimit: 1
  });
});

product.rb

class Product
    has_many :user_products
    has_many :users, :through => :user_products
end

products_controller.rb

class ProductsController

  def index
    @products = Product.where("name like ?", "%#{params[:q]}%")

    respond_to do |format|
      format.json { render :json => @products.map(&:attributes) } # This here
    end
  end

user_product.rb

class UserProduct
    attr_accessible :product_token
    belongs_to :user
    belongs_to :product
    attr_reader :product_token

    def product_token=(id)
        self.product_id = id
    end
end

user_products_controller.rb

class UserProductsController
  def new
    @user_product = current_user.user_products.build

    # This line below is for TokenInput to work, This allowed me to use @products.map on the form.
    @products = []
  end

  def edit
    @user_product = UserProduct.find(params[:id])

    # This line below had to find the Product associated with the UserProduct
    @products = [@user_product.product]
  end
end