Reservation.last.card => NoMethodError：#<Reservation:0x0090d440e130>的未定义方法‘`card’，您的意思是？card_id

Question

我确信这真的很愚蠢，但我似乎找不到问题所在。

我正在尝试调用Reservation.last.card，但收到错误

Reservation Load (0.3ms)  SELECT  "reservations".* FROM "reservations" ORDER BY "reservations"."id" DESC LIMIT $1  [["LIMIT", 1]]
NoMethodError: undefined method `card' for #<Reservation:0x090d440e130>
Did you mean?  card_id

迁移+模式

class AddCardToReservations < ActiveRecord::Migration[5.2]
  def change
    add_reference :reservations, :card, foreign_key: true
  end
end

create_table "reservations", force: :cascade do |t|
    t.bigint "park_id"
    t.bigint "card_id"
    t.index ["card_id"], name: "index_reservations_on_card_id"
    t.index ["park_id"], name: "index_reservations_on_park_id"
  end

模型

class Reservation < ApplicationRecord
  has_one :card
  belongs_to :park
end

class Card < ApplicationRecord
  belongs_to :park
  has_many :reservations
end

Answer 1

Reservation类中的代码行...

has_one :card

暗示card对象有一个不是这样的reservation_id，在reservation对象中的外键是card_id，所以您想要的是...

belongs_to :card