如何访问fields_for对象的关联方法？

Question

我很难以深度嵌套的形式访问fields_for对象的关联方法。 你能帮我了解我哪里出错了吗？

机会模型：

class Opportunity < ActiveRecord::Base
  has_many :seedlings
  accepts_nested_attributes_for :seedlings
end

苗木模型：

class Seedling < ActiveRecord::Base
  belongs_to :opportunity
  belongs_to :potential_building
  accepts_nested_attributes_for :potential_building
end

潜力构建模型：

class PotentialBuilding < ActiveRecord::Base
  has_many :seedlings
end

我希望我能在hidden_field旁边写下potential_building的名字，但我显然不明白一些事情。 我可以将potential_building_id写入页面，如下所示（Haml）：

...
= opportunity_form.fields_for :seedlings do |seedling_form|
  = seedling_form.hidden_field :potential_building_id
  = seedling_form.object.potential_building_id # => 73
....

我希望访问协会的方法会像这样简单，我不明白为什么不这样做。

...
= opportunity_form.fields_for :seedlings do |seedling_form|
  = seedling_form.hidden_field :potential_building_id
  = seedling_form.object.potential_building.name # => undefined method `name' for nil:NilClass
...

你能帮我理解吗？谢谢。

Answer 1

class Opportunity < ActiveRecord::Base
  has_many :seedlings
  accepts_nested_attributes_for :seedlings
end

http://currentricity.wordpress.com/2011/09/04/the-definitive-guide-to-accepts_nested_attributes_for-a-model-in-rails-3/