AssociationTypeMisMatch：如何使用接受 JSON 的 RESTful API (Rails) 创建对象和关联（嵌套）对象？答案

【问题标题】：AssociationTypeMisMatch: How can I create an object and associated (nested) objects with RESTful API (Rails) accepting JSON?AssociationTypeMisMatch：如何使用接受 JSON 的 RESTful API (Rails) 创建对象和关联（嵌套）对象？
【发布时间】：2019-05-15 01:24:53
【问题描述】：

我已经尝试了几个小时，但我似乎无法理解我做错了什么。出于演示目的，我简化了示例。

单独创建Car 对象是可行的，但将Wheel 对象附加到它会导致ActiveRecord::AssociationTypeMisMatch。

鉴于汽车和车轮类

class Car < ApplicationRecord
  has_many :wheels

  validates :max_speed_in_kmh,
            :name, presence: true
end


class Wheel < ApplicationRecord
  has_one :car

  validates :thickness_in_cm,
            :place, presence: true
end

还有一个 CarsController

module Api
  module V1
    class CarsController < ApplicationController

      # POST /cars
      def create
        @car = Car.create!(car_params)
        json_response(@car, :ok)
      end

      private

      def car_params
        params.permit(
          :max_speed_in_kmh,
          :name,
          { wheels: [:place, :thickness_in_cm] }
        )
      end
    end
  end
end

echo '{"name":"Kid","max_speed_in_kmh":300,"wheels":[{"thickness_in_cm":70, "place":"front"},{"thickness_in_cm":75, "place":"rear"}]}' | http POST httpbin.org/post

... "json": { "max_speed_in_kmh": 300, "name": "Kid", "wheels": [ { "place": "front", "thickness_in_cm": 70 }, { "place": "rear", "thickness_in_cm": 75 } ] }, ...

JSON 格式正确。撇开轮子，Car 对象被创建并持久化。使用Wheel 对象，控制器返回

status 500 error Internal Server Error exception #<ActiveRecord::AssociationTypeMismatch: Wheel(#70285481379180) expected, got {"place"=>"front", "thickness_in_cm"=>75} which is an instance of ActiveSupport::HashWithIndifferentAccess(#70285479411000)>

【问题讨论】：

控制器中的预算是什么？
我在简化示例时忘记重命名它。固定的。我是说汽车。 @Rthi

标签： ruby-on-rails json api nested

【解决方案1】：

如果你想和轮子一起创建汽车，你需要使用accepts_nested_attributes_for

添加到汽车模型accepts_nested_attributes_for :wheels 并将强参数更改为

  def car_params
    params.permit(
      :max_speed_in_kmh,
      :name,
      { wheels_attributes: [:id, :place, :thickness_in_cm] }
    )
  end

【讨论】：