Nested forms not storing data into database in rails 4 -

i have vendor model, product model, , vendor_product model. in vendors form, have used nested form create vendor_products attributes vendor_id, product_id , copies.on creating new vendor, creates vendor_product. reason, not stores vendor_id , product_id in vendor_products table stores copies

my associations follows

a vendor ->

        has_many :vendor_products         has_many :products, through: :vendor_products 

a product ->

        has_many :vendor_products         has_many :vendors, through: :vendor_products 

a vendor_product

        belongs_to :vendor         belongs_to :product 

vendor.rb

class vendor < activerecord::base    has_many :vendor_products   has_many :products, through: :vendor_products   accepts_nested_attributes_for :vendor_products, :products,   :allow_destroy => true  end 

my vendors/_form.html.erb

<%= form_for(@vendor) |f| %> <% if @vendor.errors.any? %> <div id="error_explanation">   <h2><%= pluralize(@vendor.errors.count, "error") %> prohibited   vendor being saved:</h2>    <ul>   <% @vendor.errors.full_messages.each |message| %>     <li><%= message %></li>   <% end %>   </ul>   </div>  <% end %>    <div class="field">    <%= f.label :name %><br>    <%= f.text_field :name %>  </div>     :     :     :  <%= f.fields_for :vendor_products |vproducts| %>   <div class="field">   <%= vproducts.label :product %><br>     <%= collection_select(:product, :product_ids, product.all, :id,     :product_name,              {:prompt => 'please select', :multiple => true }) %>   </div>   <div class="field">     <%= vproducts.label :copies %><br>     <%= vproducts.number_field :copies %>   </div>   <% end %>   <div class="actions">   <%= f.submit %> </div> <% end %> 

my vendors_controller.rb

class vendorscontroller < applicationcontroller       before_action :set_vendor, only: [:show, :edit, :update, :destroy]       respond_to :json        def index         @vendors = vendor.all.limit(20)       end         def show        end          def new          @vendor = vendor.new         @vendor.products.build         @vendor.vendor_products.build       end         def edit       end         def create         @vendor = vendor.new(vendor_params)                respond_to |format|          if @vendor.save             format.html { redirect_to @vendor, notice: 'vendor         created.' }            format.json { render :show, status: :created, location: @vendor    }          else            format.html { render :new }            format.json { render json: @vendor.errors, status:             :unprocessable_entity }          end        end       end        def update         respond_to |format|         if @vendor.update(vendor_params)            format.html { redirect_to @vendor, notice: 'vendor        updated.' }            format.json { render :show, status: :ok, location: @vendor }         else           format.html { render :edit }           format.json { render json: @vendor.errors, status:       :unprocessable_entity }         end       end     end          private        def set_vendor         @vendor = vendor.find(params[:id])       end        def vendor_params          params.require(:vendor).permit(:name, :email, :phone_no, :addressline1,        :addressline2, :landmark,       :city, :state, :country, :pincode, :latitude, :longitude, :status,          product_attributes: [:product_id, :product_name, :price ],          vendor_products: [:vendor_product_id, :vendor_id, :product_id,          :copies])       end     end 

now vendor , vendorproduct created vendor_product looks lik this

    {"id":3,      "vendor_id":null,      "product_id":null,      "copies":4,     } 

can 1 point out how fix this. doing wrong. please bear in mind rails newbie.

change once vendor_products vendor_products_attributes , 

in view

<%= collection_select(:product, :product_ids, product.all, :id,     :product_name,              {:prompt => 'please select', :multiple => true }) %>  replace   <%= vproducts.select :product_id, options_from_collection_for_select(product.all, "id", "name"), prompt: "select something" %>