Rails has_many:通过关联:通过外键检索外键属性

Question

在我们的Rails应用程序中，有三种型号：

class User < ActiveRecord::Base
  has_many :administrations, dependent: :destroy
  has_many :calendars, through: :administrations
end
class Administration < ActiveRecord::Base
  belongs_to :user
  belongs_to :calendar
end
class Calendar < ActiveRecord::Base
  has_many :administrations, dependent: :destroy
  has_many :users, through: :administrations
end

以下是相应的迁移：

class CreateUsers < ActiveRecord::Migration
  def change
    create_table :users do |t|
      t.string :first_name
      t.string :last_name
      t.string :email
      t.timestamps null: false
    end
  end
end
class CreateAdministrations < ActiveRecord::Migration
  def change
    create_table :administrations do |t|
      t.references :user, index: true, foreign_key: true
      t.references :calendar, index: true, foreign_key: true
      t.string :role
      t.timestamps null: false
    end
  end
end
class CreateCalendars < ActiveRecord::Migration
  def change
    create_table :calendars do |t|
      t.string :name
      t.timestamps null: false
    end
  end
end

编辑：这也是我们的UsersController:

class UsersController < ApplicationController
  before_action :logged_in_user, only: [:edit, :update, :destroy]
  before_action :correct_user,   only: [:edit, :update]
  before_action :admin_user,     only: [:index, :destroy]
  def index
    @users = User.paginate(page: params[:page], :per_page => 10)
  end
  def show
    @user = User.find(params[:id])
    @administrations = @user.administrations
    @calendar = current_user.calendars.build if logged_in?
  end
  def new
    @user = User.new
  end
  def create
    @user = User.new(user_params)
    if @user.save
      @user.send_activation_email
      flash[:info] = "Please check your email to activate your account."
      redirect_to root_url
    else
      render 'new'
    end
  end
  def edit
    @user = User.find(params[:id])
  end
  def update
    @user = User.find(params[:id])
    if @user.update_attributes(user_params)
      flash[:success] = "Profile updated"
      redirect_to @user
    else
      render 'edit'
    end
  end
  def destroy
    User.find(params[:id]).destroy
    flash[:success] = "User deleted"
    redirect_to users_url
  end
  private
    def user_params
      params.require(:user).permit(:first_name, :last_name, :email,
                                    :password, :password_confirmation)
    end
    # Before filters
    # Confirms the correct user.
    def correct_user
      @user = User.find(params[:id])
      redirect_to(root_url) unless current_user?(@user)
    end
    # Confirms an admin user.
    def admin_user
      redirect_to(root_url) unless current_user.try(:admin?)
    end
end

一旦用户登录（身份验证系统已经启动并运行），我们希望在他的个人资料（users#show）中显示他创建的所有日历。

我们在数据库中植入了以下实例：

User.create!(first_name:  "Andy") # This user's id is 1.
Calendar.create!(name: "CalendarA")
Calendar.create!(name: "CalendarB")
Calendar.create!(name: "CalendarC")
Administration.create!(user_id: 1, calendar_id: 1, role: "Creator")
Administration.create!(user_id: 1, calendar_id: 2, role: "Editor")
Administration.create!(user_id: 1, calendar_id: 3, role: "Viewer")

然后，我们创建了一个_administration.html.erb部分：

<li id="administration-<%= administration.id %>">
  <span class="name"><%= administration.calendar_id %></span>
</li>

并将其包含在我们的用户show.html.erb文件中：

<p><%= @user.first_name %>'s calendars</p>
<% if @user.administrations.any? %>
<%= render @administrations %>
<% end %>

这是有效的，我们得到：

安迪的日历：

• 1
• 2
• 3

然而，我们希望为每个用户获得的不仅仅是他的日历的id s，还有他们的name s，如下所示：

安迪的日历：

• 1日历A
• 2日历B
• 3日历C

因此，我们尝试更新_administration.html.erb部分如下：

<li id="administration-<%= administration.id %>">
  <span class="name"><%= administration.calendar_id.name %></span>
</li>

这导致以下错误：

NoMethodError in UsersController#show
undefined method `name' for 1:Fixnum
Application Trace | Framework Trace | Full Trace
app/views/administrations/_administration.html.erb:2:in `_app_views_administrations__administration_html_erb__2225316747000531998_70329866860100'
app/views/users/show.html.erb:32:in `_app_views_users_show_html_erb___891585127045041471_70329832995240'

如何通过join administration模型中的外键calendar_id从calendar模型访问"foreign"属性name？

Answer 1

administration.calendar.name应该可以工作。

或者，您可以将此方法添加到Administration:

def calendar_name
  calendar.name
end

然后只调用administration.calendar_name