在 ruby​​ on rails 应用程序中重用模型

Question

我目前正在将 cmets 添加到我的一个模型 MaintenanceRequest 并想知道我应该如何去做。

我有一个模型Offer，它已经构建了 cmets，并使用 ActionCable 设置如下

# models/comment.rb

class Comment < ApplicationRecord
  belongs_to :user
  belongs_to :offer
end

# channels/comment_channel.rb

class CommentChannel < ApplicationCable::Channel
  def subscribed
    offer = Offer.find params[:offer]
    stream_for offer
  end
end

评论控制器看起来像

# controllers/comments_controller.rb

class CommentsController < ApplicationController
  before_action :authenticate_user!
  before_action :is_valid_offer

  def create
    offer = Offer.find(comment_params[:offer_id])

    if comment_params[:content].blank?
      # return redirect_to request.referrer, alert: 'Comment cannot be empty.'
      return render json: {success: false}
    end

    if offer.user_id != current_user.id && offer.landlord_id != current_user.id
      return render json: {success: false}
    end

    @comment = Comment.new(
      user_id: current_user.id,
      offer_id: offer.id,
      content: comment_params[:content],
    )

    if @comment.save
      # redirect_to request.referrer, notice: 'Comment sent.'
      CommentChannel.broadcast_to offer, message: render_comment(@comment)
      render json: {success: true}
    else
      redirect_to request.referrer, alert: "Couldn't send comment."
      render json: {success: true}
    end
  end
end

我的问题是，有没有一种方法可以为属于 MaintenanceRequest 的 cmets 使用相同的模型，或者我应该为那里的 cmets 创建新模型和控制器？如果我尝试重用当前的评论模型，这似乎会变得非常混乱。这里的“最佳做法”是什么？

Answer 1

如果你想创建一个可重用的关联，你想使用多态关联：

class Comment < ApplicationRecord
  belongs_to :user
  belongs_to :commentable, 
    polymorphic: true

  validates :content, 
    presence: true
end

不是使用单个列保存指向固定表的整数，而是通过使用一列作为其他表的主键并将实体的类名存储在字符串列中来“欺骗”关系数据库模型（在这个例子叫commentable_type)。

您可以在生成迁移（或模型）时通过传递多态选项来创建所需的列：

rails g migration add_commentable_to_comments commentable:belongs_to{polymorphic}

但是，控制器的操作有点像火车残骸。它应该看起来更像这样：

class CommentsController < ApplicationController
  before_action :authenticate_user!
  before_action :set_offer
  before_action :authorize_user

  def create
    @comment = @offer.comments.new(comment_params) do |c|
      c.user = current_user
    end

    if @comment.save
      # redirect_to request.referrer, notice: 'Comment sent.'
      CommentChannel.broadcast_to offer, message: render_comment(@comment)
      # rendering json here is actually just stupid. Just use a HTTP status code 
      # as a response if you're not actually returning the rendered entity.
      render json: { success: true }, 
        status: :created,
        location: @comment
    else
      # either return JSON which is actually useful or just a status code
      render json: { success: false }, 
        status: :unprocessable_entity
    end
  end

  private

  def set_offer
    @offer = Offer.find(params[:offer_id])
  end

  # this should be extracted to an authorization layer such as Pundit
  def authorize_offer
    if @offer.user_id != current_user.id && @offer.landlord_id != current_user.id 
      render json: { success: false },
        status: :unauthorized
    end
  end
end

有两种方法可以将此控制器重新用于不同类型的“评论”。您可以在单个控制器中检查 offer_id 或 maintenance_request_id 的存在并使用它来推断类，或者您可以使用继承来更好地分配职责：

# routes.rb

resources :offers do
  resources :comments, 
    only: :create,
    module: :offers
end

resources :maintainence_requests do
  resources :comments, 
    only: :create,
    module: :maintainence_requests
end

class CommentsController
  before_action :set_commentable, only: [:new, :create, :index]
  before_action :authenticate_user!
  attr_reader :commentable

  def create
    @comment = commentable.comments.new(comment_params) do |c|
      c.user = current_user
    end
    if @comment.save
      # simple extendability feature that lets you "tap into" the flow 
      # by passing a block when calling super in subclasses
      yield @comment if block_given?
      render json: @comment,
             status: :created
    else
      render json: { errors: @comment.errors.full_messages },
             status: :unprocessable_entity
    end
  end

  
  private

  # Uses simple heuristics based on module nesting to guess the name of the model
  # that is being commented upon. Overide if needed.
  # @example Foos::BarsController -> Foo
  def commentable_class
    @commentable_class ||= self.class.module_parent.name.singularize.constantize
  end 

  def commentable_param_key
    commentable_class.model_name.param_key
  end

  def set_commentable
    @commentable = commentable_class.find("#{commentable_param_key}_id")
  end

  def comment_params
    params.require(:comment)
          .permit(:content)
  end
end

module Offers
  class CommentsController < ::CommentsController
    # POST /offers/:offer_id/comments
    def create
      # block is called after a comment is succesfully saved but before 
      # the response is set
      super do |comment|
        CommentChannel.broadcast_to comment.offer, 
          message: render_comment(comment) 
      end
    end
  end
end

module MaintainenceRequests
  class CommentsController < ::CommentsController
  end
end