Rails has_one：through - undefined方法create_

Question

我收到了这个错误：

undefined method `create_postconversation' for #<Post...>

......源于这一行：

posts_controller.rb

@postconversation = @post.create_postconversation

我做错了什么？

post.rb

has_one :postconvo, foreign_key: "post_id", dependent: :destroy
has_one :postconversation,  through: :postconvo,
                            class_name: "Conversation",
                            source: :conversation

postconvo.rb

belongs_to :post
belongs_to :conversation

validates :post_id, presence: true
validates :conversation_id, presence: true

conversation.rb

has_one :postconvo, foreign_key: "conversation_id", dependent: :destroy
has_one :post, through: :postconvo, source: :post