ruby on rails - Nested Form and database update -

i'm quite new rails, question may seem noobish.

i have habtm self association. product can become "combo" of products, having n products.

class product < activerecord::base   has_many :combo_elements, class_name: "comboelement", foreign_key: :combo_id   has_many :element_combos, class_name: "comboelement", foreign_key: :element_id   has_many :combos, :through => :element_combos   has_many :elements, :through => :combo_elements    accepts_nested_attributes_for :elements end  class comboelement < activerecord::base   belongs_to :combo, :class_name => 'product'   belongs_to :element, :class_name => 'product' end 

with above code, can list "elements" of combo. can list "combos" product part of (the comboelement table has combo_id , element_id)

here form

<%= f.simple_fields_for :elements, @element |b| %>   <%= b.input :element_id, :collection => product.all.collect{ |t| [t.name, t.id ]}, selected: b.object.id %>   <%= b.link_to_remove "remove element" %> <% end %> 

i can list products combo has, whenever try update, doesn't work.

my product controller has following code

def product_params   params[:product].permit(:name, :price, elements_attributes: [:id, :element_id, :_destroy]) end 

i appreciate help. in advance!