Rails-style polymorphic model in ember-data

Question

If I have the following models in Rails, how would I represent this in Ember/Ember Data?

class Attachment < ActiveRecord::Base
  belongs_to :user
  belongs_to :attachable, polymorphic: true
end

class Profile < ActiveRecord::Base
  belongs_to :user
  has_one :photo, class_name: 'Attachment', as: :attachable
end

class Post < ActiveRecord::Base
  belongs_to :user
  has_many :attachments, as: :attachable
end

References I've found are the relevant ember-data pull request, the ember-data tests for polymorphic relationships, and this related question but it's difficult to work out a canonical example from them.

Answer 1

I now use two different ways of working with rails-style "polymorphic" models. I have updated the code below to show both uses.

Attachment model: This is "polymorphic" on the Rails side but is always "embedded" on the Ember side. The reason for this is that I currently only need to save/update attachments along with their associated model.

Comment model: This is polymorphic on both the Rails side and the Ember side.

I have also included code for the Post model as it can have multiple attachments and multiple comments.

---

Rails code:

class Attachment < ActiveRecord::Base
  belongs_to :user
  belongs_to :attachable, polymorphic: true
end

class Comment < ActiveRecord::Base
  belongs_to :user
  belongs_to :commentable, polymorphic: true
end

class Post < ActiveRecord::Base
  belongs_to :user
  has_many :attachments, as: :attachable
  has_many :comments, as: :commentable
end

class ApplicationSerializer < ActiveModel::Serializer
  embed :ids, include: true
end

class AttachmentSerializer < ApplicationSerializer
  attributes :id, :url, :errors
  has_many :comments
end

class CommentSerializer < ApplicationSerializer
  attributes :id, :body, :created_at, :commentable_id, :commentable_type
  has_one :user
end

class PostSerializer < ApplicationSerializer
  attributes :id, :title, :body, :posted_at, :errors
  has_one :user
  has_many :attachments, embed: :objects, include: true
  has_many :comments
end

class Api::V1::PostsController < Api::V1::BaseController
  before_filter :auth_only!, only: :create

  def create
    # clean / capture ember-data supplied arguments
    params[:post].delete(:user_id)
    attachments_params = params[:post].delete(:attachments)

    @post = current_user.posts.new(params[:post])
    process_attachments(attachments_params)

    if @post.save
      render json: @post, status: 201
    else
      warden.custom_failure!
      render json: @post, status: 422
    end
  end

  protected

    def process_attachments(attachments_params)
      return unless attachments_params.present?

      attachments_params.each do |attachment_params|
        # ignore ember-data's additional keys
        attachment_params.delete(:created_at)
        attachment_params.delete(:user_id)

        attachment = @post.attachments.new(attachment_params)
        attachment.user = current_user
      end
    end
end

Ember code:

DS.RESTAdapter.configure 'App.Post',
  alias: 'Post'

DS.RESTAdapter.map 'App.Post',
  attachments: { embedded: 'always' }

App.Store = DS.Store.extend
  adapter: DS.RESTAdapter.create
    namespace: 'api/v1'

App.Comment = App.Model.extend
  user: DS.belongsTo('App.User')
  commentable: DS.belongsTo('App.Commentable', { polymorphic: true })
  body:       DS.attr('string')
  createdAt:  DS.attr('date')

App.Commentable = App.Model.extend
  comments: DS.hasMany('App.Comment')

App.Attachment = App.Commentable.extend
  user: DS.belongsTo('App.User')
  url: DS.attr('string')

App.Post = App.Commentable.extend
  user: DS.belongsTo('App.User')
  attachments: DS.hasMany('App.Attachment')

  title: DS.attr('string')
  body: DS.attr('string')
  postedAt: DS.attr('date')

App.PostFormOverlayController = App.OverlayController.extend
  # 'files' attribute is set by a widget that wraps the filepicker.io JS
  updateAttachments: (->
    attachments = @get('attachments')
    attachments.clear()
    @get('files').forEach (file) =>
      attachment = App.Attachment.createRecord({fpFile: file})
      attachments.addObject(attachment)
  ).observes('files')

App.CommentNewController = App.ObjectController.extend
  # this should be instantiated with it's model set to the commentable
  # item. eg. `{{render 'comment/new' content}}`

  save: ->
    transaction = @get('store').transaction()
    comment = transaction.createRecord App.Comment,
      body: @get('body')
      commentable: @get('model')

    comment.one 'didCreate', @, ->
      @set('body', null)

    transaction.commit()

Unfortunately my Rails code has become a little polluted with ember-data specific oddities as it tries to send back all the attributes that are defined on the models. (Note: There is an open proposal for read-only attributes that would solve the params pollution issue)

If anyone knows a better way to approach any of the above please let me know!

NB: I'm a little concerned that having models extend from App.Commentable will prevent me from having multiple polymorphic attachments on a model, I may need to look for a different way of handling that.

Answer 2

The Comment part of Kevin Ansfield's answer (didn't use the Post part) works as of Ember 1.3.0-beta / Ember Data 1.0.0-beta.4 except for the rails serializer, which should now be:

class CommentSerializer < ActiveModel::Serializer
  attributes :id, :body, :created_at, :commentable_id, :commentable_type
  has_one :user

  def attributes
    data = super
    data[:commentable] = {id: data[:commentable_id], type: data[:commentable_type]}
    data.delete(:commentable_type)
    data.delete(:commentable_id)
    data
  end