Rails：嵌套模型不保存关联

Question

我有两个模型，Trips和Locations。旅行的起点和目的地都是对位置的引用：

class Trip < ActiveRecord::Base

  attr_accessible :name, :destination, :origin, :start_datetime, :transportation, :trip_type, :destination_attributes, :origin_attributes

  enum_attr :trip_type, %w(Hitchhiker Driver)

  has_one :origin, :class_name => 'Location' , :primary_key => :origin, :foreign_key => :id
  has_one :destination, :class_name => 'Location' , :primary_key => :destination, :foreign_key => :id

  accepts_nested_attributes_for :origin, :allow_destroy => true
  accepts_nested_attributes_for :destination, :allow_destroy => true

  belongs_to :user

  validates_presence_of :name, :destination, :origin, :start_datetime, :transportation, :trip_type

end


class Location < ActiveRecord::Base
  attr_accessible :address, :latitude, :longitude

  geocoded_by :address

  before_validation :geocode

  validates_presence_of :address
  validate :geocoding_was_found

  def geocoding_was_found
    errors.add(:address, 'is not valid') if latitude.nil? || longitude.nil?
  end

end

在控制器中调用create时，它会保存所有记录（两个位置记录和行程记录），但不保存关联。

def create

    @trip = Trip.new(params[:trip])
    @trip.user = current_user

    respond_to do |format|
      if @trip.save
        format.html { redirect_to @trip, notice: 'Trip was successfully created.' }
        format.json { render json: @trip, status: :created, location: @trip }
      else
        format.html { render action: "new" }
        format.json { render json: @trip.errors, status: :unprocessable_entity }
      end
    end
  end

我正在使用嵌套表单，因此通过origin_attributes和destination_attributes传递location的数据。我的猜测是因为这两个字段被称为origin和destination而不是_id。