ModelTransporter

Syndicate Rails model updates to your client-side Redux store via Action Cable.

If you have many users viewing the same objects in different sessions, stored in Redux or a similar client-side store, ModelTransporter allows updates made by one client to flow to the others instantly. Since clients typically update models via web requests, ModelTransporter batches updates from each request together so that listeners see changes to all related objects at once.

Add this line to your application's Gemfile:

gem 'model_transporter'

Sync updates for a model via:

class MyModel < ApplicationRecord
  notifies_model_updates channel: -> { MyChannel.broadcasting_for(self) }
end

The channel tells ModelTransporter which listeners to notify, and also serves as a grouping key for updates within a single web request. In the above example, if you had a channel defined as:

class MyChannel < ApplicationCable::Channel
  def subscribed
    my_model = MyModel.find(params[:id])
    stream_for my_model
  end
end

Then any client connected to that channel would receive push updates for changes to that model.

If you had a TodoList app with TodoList objects that were shared between users, Todos that belong to TodoLists, and TodoComments that belong to Todos, you could set it up as follows to ensure all clients on the same TodoList page get real-time updates from other users to stay in sync:

class TodoList < ApplicationRecord
  has_many :todos, dependent: :destroy

  notifies_model_updates channel: -> { TodoListChannel.broadcasting_for(self) }
end

class Todo < ApplicationRecord
  belongs_to :todo_list
  has_many :todo_comments, dependent: :destroy

  notifies_model_updates channel: -> { TodoListChannel.broadcasting_for(todo_list) }
end

class TodoComment < ApplicationRecord
  belongs_to :todo

  notifies_model_updates channel: -> { TodoListChannel.broadcasting_for(todo.todo_list) }
end

Since all 3 objects use the same parent TodoList object, any request that updates one or more of these objects at the same time, e.g. deleting a Todo and its dependent comments, would batch all of those changes and send them to everyone listening on the TodoListChannel for that TodoList.

Payloads follow a simple standard format:

{
  type: 'server_event/MODEL_UPDATES',
  actor_id: ACTOR_ID,
  {
    creates: {
      MODEL_NAME: {
        MODEL_ID: MODEL_JSON
      },
      MODEL_2_NAME: { ... }
    }
    updates: {
      MODEL_NAME: {
        MODEL_ID: MODEL_JSON
      },
      MODEL_2_NAME: { ... }
    }
    deletes: {
      MODEL_NAME: {
        MODEL_ID: {}
      },
      MODEL_2_NAME: { ... }
    }
  }
}

ModelTransporter simply sends these messages, by default serializing objects as json by calling as_json, it is your job to handle them on the client side in the way that makes sense, e.g. by updating objects in your Redux store.

ModelTransporter.configure do |config|
  config.actor = :current_user
  config.push_adapter = MyPushAdapter.new
end

• actor: ModelTransporter includes an actor_id in message payloads, which can be useful if you want to determine who triggered a model update. If you have a controller method called current_user, you can set actor equal to :current_user, and actor_id in transporter payloads will get set to that user
• push_adapter: by default ModelTransporter assumes you want to send updates via ActionCable. If you want to send updates in another way, e.g. something like Pusher, set a custom push_adapter to anything that responds to push_update(channel, message). The default action cable push adapter, for reference, is:

# lib/model_transporter/pusher_adapter/action_cable.rb
module ModelTransporter
  module PushAdapter
    class ActionCable
      def push_update(channel, message)
        # broadcast can take a coder option as well, which by default is `coder: ActiveSupport::JSON`
        ::ActionCable.server.broadcast(channel, message)
      end
    end
  end
end

If you want to batch updates outside of a web request, e.g. if you are updating models in a background job, or as a result of messages received over websockets, you can manually batch all updates inside of a block via:

ModelTransporter::BatchModelUpdates.batch_model_updates do
  # update multiple models
end

rake spec

The gem is available as open source under the terms of the MIT License.