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我很難以深度嵌套的形式訪問fields_for對象的關聯方法。你能幫我理解我哪裏出錯了嗎？如何訪問fields_for對象的關聯方法？
機遇型號：
class Opportunity < ActiveRecord::Base
has_many :seedlings
accepts_nested_attributes_for :seedlings
end
幼苗型號：
class Seedling < ActiveRecord::Base
belongs_to :opportunity
belongs_to :potential_building
accepts_nested_attributes_for :potential_building
end
PotentialBuilding型號：
class PotentialBuilding < ActiveRecord::Base
has_many :seedlings
end
我希望我能寫hidden_field旁邊的potential_building的名字，但我顯然不理解某事。我可以寫potential_building_id頁面，像這樣（HAML）：
...
= opportunity_form.fields_for :seedlings do |seedling_form|
= seedling_form.hidden_field :potential_building_id
= seedling_form.object.potential_building_id # => 73
....
我希望訪問該協會的方法將是，因爲這容易，我不明白爲什麼它不是。
...
= 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
...
你能幫我理解嗎？謝謝。