设计多态关联：如何修复“用户元必须存在”错误

Question

我正在开发一个Rails 5项目，我正在使用Device使用多态关系创建多个模型，如下所示：

class DeviseCreateUsers < ActiveRecord::Migration[5.0]
  def change
    create_table :users do |t|

      t.string :meta_type
      t.integer :meta_id

      ## Database authenticatable
      t.string :email,              null: false, default: ""
      t.string :encrypted_password, null: false, default: ""

      ## Recoverable
      t.string   :reset_password_token
      t.datetime :reset_password_sent_at

      ## Rememberable
      t.datetime :remember_created_at

      ## Trackable
      t.integer  :sign_in_count, default: 0, null: false
      t.datetime :current_sign_in_at
      t.datetime :last_sign_in_at
      t.string   :current_sign_in_ip
      t.string   :last_sign_in_ip

      ## Confirmable
      # t.string   :confirmation_token
      # t.datetime :confirmed_at
      # t.datetime :confirmation_sent_at
      # t.string   :unconfirmed_email # Only if using reconfirmable

      ## Lockable
      # t.integer  :failed_attempts, default: 0, null: false # Only if lock strategy is :failed_attempts
      # t.string   :unlock_token # Only if unlock strategy is :email or :both
      # t.datetime :locked_at


      t.timestamps null: false
    end

    add_index :users, :email,                unique: true
    add_index :users, :reset_password_token, unique: true
    add_index :users, :meta_id
    add_index :users, :meta_type
    # add_index :users, :confirmation_token,   unique: true
    # add_index :users, :unlock_token,         unique: true
  end
end

user.rb

class User < ApplicationRecord
  # Include default devise modules. Others available are:
  # :confirmable, :lockable, :timeoutable and :omniauthable
  devise :database_authenticatable, :registerable,
         :recoverable, :rememberable, :trackable, :validatable

  belongs_to :meta, polymorphic: true
end

我有一个Caregiver课程（我稍后会添加护理人员特定的字段）

class CreateCaregivers < ActiveRecord::Migration[5.0]
  def change
    create_table :caregivers do |t|

      t.timestamps
    end
  end
end

caregiver.rb

class Caregiver < ApplicationRecord
  has_one :user, as: :meta, dependent: :destroy
  accepts_nested_attributes_for :user
end

我为照顾者类搭建了控制器。这是文件：

class CaregiversController < ApplicationController
  before_action :set_caregiver, only: [:show, :edit, :update, :destroy]

  # GET /caregivers
  # GET /caregivers.json
  def index
    @caregivers = Caregiver.all
  end

  # GET /caregivers/1
  # GET /caregivers/1.json
  def show
  end

  # GET /caregivers/new
  def new
    @caregiver = Caregiver.new
    @caregiver.build_user
  end

  # GET /caregivers/1/edit
  def edit
  end

  # POST /caregivers
  # POST /caregivers.json
  def create
    @caregiver = Caregiver.new(caregiver_params)

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

  # PATCH/PUT /caregivers/1
  # PATCH/PUT /caregivers/1.json
  def update
    respond_to do |format|
      if @caregiver.update(caregiver_params)
        format.html { redirect_to @caregiver, notice: 'Caregiver was successfully updated.' }
        format.json { render :show, status: :ok, location: @caregiver }
      else
        format.html { render :edit }
        format.json { render json: @caregiver.errors, status: :unprocessable_entity }
      end
    end
  end

  # DELETE /caregivers/1
  # DELETE /caregivers/1.json
  def destroy
    @caregiver.destroy
    respond_to do |format|
      format.html { redirect_to caregivers_url, notice: 'Caregiver was successfully destroyed.' }
      format.json { head :no_content }
    end
  end

  private
    # Use callbacks to share common setup or constraints between actions.
    def set_caregiver
      @caregiver = Caregiver.find(params[:id])
    end

    # Never trust parameters from the scary internet, only allow the white list through.
    def caregiver_params
      params.require(:caregiver).permit(user_attributes: [ :id, :email, :password, :password_confirmation ])
    end
end

这是创建表单

<%= form_for(@caregiver) do |f| %>
  <% if @caregiver.errors.any? %>
    <div id="error_explanation">
      <h2><%= pluralize(@caregiver.errors.count, "error") %> prohibited this caregiver from being saved:</h2>

      <ul>
        <% caregiver.errors.full_messages.each do |message| %>
        <li><%= message %></li>
        <% end %>
      </ul>
    </div>
  <% end %>

  <%= f.fields_for :user do |u| %>
  <div class="col-lg-6">
    <%= u.label :email %><br>
    <%= u.text_field :email %>
  </div>

  <div class="col-lg-6">
    <%= u.label :password %><br>
    <%= u.text_field :password %>
  </div>

  <div class="col-lg-6">
    <%= u.label :password_confirmation %><br>
    <%= u.text_field :password_confirmation %>
  </div>
  <% end %>


  <div class="actions">
    <%= f.submit %>
  </div>
<% end %>

我正在关注this示例。

Github上的示例运行正常。但是，当我尝试创建新的看护者记录时，我收到以下错误：

  

用户元必须存在

我无法找到错误。

Answer 1

Rails 5默认需要belongs_to关联。要禁用它，您需要将optional: true添加到belongs_to

belongs_to :meta, polymorphic: true, optional: true