activerecord - rails fields_for object is nil, when I try to access an attribute -

have 3 models:

class offer < activerecord::base    has_many :offer_items end  class offeritem < activerecord::base   belongs_to :offer   belongs_to :partner_product   accepts_nested_attributes_for :partner_product end  class partnerproduct < activerecord::base  has_many :offer_items  accepts_nested_attributes_for :offer_items end 

in form offer edited, there fields_for edit offer_item

<% f.fields_for :offer_items |offer_item_form| -%>  <div class='offer_item'>    <%= render :partial => 'offer_item_fields', :locals => {:offer_item_form => offer_item_form}%>       </div> <% end -%> 

the code chunk in partial:

<%= offer_item_form.object.partner_product.name%> 

throws error

undefined method `name' nil:nilclass

extracted source (around line #29):

<%= offer_item_form.object.partner_product.name%> 

but when don't ask name, this

<%= offer_item_form.object.partner_product%> <%= debug( offer_item_form.object.partner_product)%> 

get in browser:

#<partnerproduct:0x007fa8785ff938>  --- !ruby/activerecord:partnerproduct  attributes:  id: 1 partner_id: 586 name: stock_volume: 0 source_price: 0 created_at: 2012-05-31 14:05:47 z updated_at: 2012-05-31 14:05:47 z 

i'm not wondering, why can't access 'name' attribute , changed partner_product nil, should show it. welcome! thanks