ruby-on-rails-3 - 简单形式的关联给出 "undefined method ` klass' for nil :NilClass"error

Question

在我的 Rails 3 应用程序中，我有以下简单的关系结构:

class Rollout < ActiveRecord::Base
    has_many :items, :through => :rollout_items
end

class RolloutItem < ActiveRecord::Base
    belongs_to :rollout
    belongs_to :item
end

class Item < ActiveRecord::Base
    has_many :rollouts, :through => :rollout_items
end

Controller :

def new
    @rollout = Rollout.new
end

我收到以下形式的上述错误:

<%= simple_form_for @rollout do |f| %>
    <%= f.association :items %>
<% end %>

Answer 1

Rollout之间存在缺失关系和 RolloutItem :

class Rollout < ActiveRecord::Base
    has_many :rollout_items # This.
    has_many :items, :through => :rollout_items
end

Item 也是如此.