Rails 3: Why the field with error is not wrapped with "field_with_errors" div when validation fails? -

my product class has price field, has appropriate column in products table in database, , new_shop helper field (which defined attr_accessor, , not has appropriate column in products table in database).

when validation on price fails, input field wrapped field_with_errors div, when validation on new_shop fails, not wrapped field_with_errors div. why ?

here generated html these input fields:

<input type="text" name="product[price]" id="product_price"> <input type="text" value="" name="product[new_shop]" id="product_new_shop"> 

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some more info:

class product < activerecord::base   attr_accessor :new_shop    accepts_nested_attributes_for :shop   validates_presence_of :price   ... end  class shop < activerecord::base   validates_presence_of :name   ... end 

when form submitted, new_shop value passed product's shop_attributes[:name].

so it's :name attribute fails validation? why new_shop doesn't fieldwitherrors div then: looks @ @product.errors decide on field field basis whether has errors. ie

#comes :new_shop field #looks see if @product.errors.on(:new_shop) not blank #if isn't blank, wraps error div round it.