ruby on rails - Creating new records with has_many through -

i trying create simple form create valuations (offers) specific goods( spare arts). valuation may have many parts selected using select form. using classes listed below. have created join table valuation_lines store valuations. when using form there no errors records missing... unfortunatelly got stuck , have no idea how create form save records in valuation_lines table?

i appreciate on issue! new rails got stuck 2 days on , have no idea how overcome this...

class valuation < activerecord::base     has_many :valuation_lines     has_many :parts, :through => :valuation_lines     accepts_nested_attributes_for :parts end  class valuationline < activerecord::base     belongs_to :part     belongs_to :valuation end  class part < activerecord::base     has_many :valuation_lines     has_many :valuations, :through => :valuation_lines end 

further form creating new valuations looks like:

<%= form_for(@valuation) |f| %>   <% if @valuation.errors.any? %>     <div id="error_explanation">       <h2><%= pluralize(@valuation.errors.count, "error") %> prohibited valuation being saved:</h2>        <ul>       <% @valuation.errors.full_messages.each |msg| %>         <li><%= msg %></li>       <% end %>       </ul>     </div>   <% end %>    <div class="field">     <%= f.label :description %><br>     <%= f.text_area :description %>   </div>    <div class="field">     <%= f.fields_for :part |builder| %>       <%= builder.label :part %><br>          <%= builder.collection_select :part_id, part.all, :id, :name %>     <% end %>   </div>    <div class="actions">     <%= f.submit %>   </div> <% end %> 

join table:

 create_table "valuation_lines", force: true |t|         t.integer "valuation_id"         t.integer "part_id"         t.integer "pruchase_price"       end 

valuation controller:

 # /valuations/new   def new     @valuation = valuation.new   end     # post /valuations   # post /valuations.json   def create     @valuation = valuation.new(valuation_params)      respond_to |format|       if @valuation.save         format.html { redirect_to @valuation, notice: 'valuation created.' }         format.json { render action: 'show', status: :created, location: @valuation }       else         format.html { render action: 'new' }         format.json { render json: @valuation.errors, status: :unprocessable_entity }       end     end   end