Sync

This started as a thought experiment that is growing into a viable option for realtime Rails apps without ditching the standard rails stack that we love and are so productive with for a heavy client side MVC framework.

Real-time partials with Rails. Sync lets you render partials for models that, with minimal code, update in realtime in the browser when changes occur on the server.

In practice, one simply only needs to replace:

<%= render partial: 'user_row', locals: {user: @user} %>

with:

<%= sync partial: 'user_row', resource: @user %>

Then update views realtime automatically with the sync DSL or with a with a simple sync_update(@user) in the controller without any extra javascript or configuration.

In addition to real-time updates, Sync also provides:

• Realtime removal of partials from the DOM when the sync'd model is destroyed in the controller via sync_destroy(@user)
• Realtime appending of newly created model's on scoped channels
• JavaScript/CoffeeScript hooks to override and extend element updates/appends/removes for partials
• Support for Faye and Pusher

• Ruby >= 1.9.2
• Rails 3 >= 3.1 or Rails 4
• jQuery >= 1.9

gem 'faye'
gem 'thin', require: false
gem 'sync'

gem 'pusher'
gem 'sync'

$ bundle
$ rails g sync:install

//= require sync

<%= javascript_include_tag Sync.adapter_javascript_url %>

Set your configuration in the generated config/sync.yml file, using the Faye adapter. Then run Faye alongside your app.

rackup sync.ru -E production

Set your configuration in the generated config/sync.yml file, using the Pusher adapter. No extra process/setup.

The current implementation uses a DOM range query (jQuery's nextUntil) to match your partial's "element" in the DOM. The way this selector works requires your sync'd partial to be wrapped in a root level html tag for that partial file. For example, this parent view/sync partial approach would not work:

Given the sync partial _todo_row.html.erb:

Title:
<%= link_to todo.title, todo %>

And the parent view:

<table>
  <tbody>
    <tr>
      <%= sync partial: 'todo_row', resource: @todo %>
    </tr>
  </tbody>
</table>

sync partial _todo_row.html.erb:

<tr> <!-- root level container for the partial required here -->
  Title:
  <%= link_to todo.title, todo %>
</tr>

And the parent view changed to:

<table>
  <tbody>
    <%= sync partial: 'todo_row', resource: @todo %>
  </tbody>
</table>

I'm currently investigating true DOM ranges via the Range object.

In addition to calling explicit sync actions within controller methods, a sync and enable_sync DSL has been added to ActionController::Base and ActiveRecord::Base to automate the syncing approach in a controlled, threadsafe way.

  class TodosController < ApplicationController

    enable_sync only: [:create, :update, :destroy]
    ...
  end

  class Todo < ActiveRecord::Base

    belongs_to :project, counter_cache: true
    has_many :comments, dependent: :destroy

    sync :all, scope: :project

  end

Sync::Actions can be included into any object wishing to perform sync publishes for a given resource. Instead of using the the controller as context for rendering, a Sync::Renderer instance is used. Since the Renderer is not part of the request/response/session, it has no knowledge of the current session (ie. current_user), so syncing from outside the controller context will require some care that the partial can be rendered within a sessionless context.

 # Inside some script/worker
  Sync::Model.enable do
    Todo.first.update title: "This todo will be sync'd on save"
  end
  Todo.first.update title: "This todo will NOT be sync'd on save"

  Sync::Model.enable!
  Todo.first.update title: "This todo will be sync'd on save"
  Todo.first.update title: "This todo will be sync'd on save"
  Todo.first.update title: "This todo will be sync'd on save"
  Sync::Model.disable!
  Todo.first.update title: "This todo will NOT be sync'd on save"

Sync allows you to hook into and override or extend all of the actions it performs when updating partials on the client side. When a sync partial is rendered, sync will instantiate a javascript View class based on the following order of lookup:

1. The camelized version of the concatenated snake case resource and partial names.
2. The camelized version of the snake cased partial name.

partial name 'list_row', resource name 'todo', order of lookup:

1. Sync.TodoListRow
2. Sync.ListRow
3. Sync.View (Default fallback)

For example, if you wanted to fade in/out a row in a sync'd todo list instead of the Sync.View default of instant insert/remove:

class Sync.TodoListRow extends Sync.View

  beforeInsert: ($el) ->
    $el.hide()
    @insert($el)

  afterInsert: -> @$el.fadeIn 'slow'

  beforeRemove: -> @$el.fadeOut 'slow', => @remove()

Sometimes, you do not want your page to update with every new record. With the scope option, you can limit what is being updated on a given page.

One way of using scope is by supplying a String or a Symbol. This is useful for example when you want to only show new records for a given locale:

View:

<%= sync_new partial: 'todo_list_row', resource: Todo.new, scope: I18n.locale %>

Controller/Model:

sync_new @todo, scope: @todo.locale

Another use of scope is with a parent resource. This way you can for example update a project page with new todos for this single project:

View:

<%= sync_new partial: 'todo_list_row', resource: Todo.new, scope: @project %>

Controller/Model:

sync_new @todo, scope: @project

Both approaches can be combined. Just supply an Array of Strings/Symbols and/or parent resources to the scope option. Note that the order of elements matters. Be sure to use the same order in your view and in your controller/model.

Refetching allows syncing partials across different users when the partial requires the session's context (ie. current_user).

Ex: View: Add refetch: true to sync calls, and place partial file in a 'refetch' subdirectory in the model's sync view folder:

The partial file would be located in app/views/sync/todos/refetch/_list_row.html.erb

<% @project.todos.ordered.each do |todo| %>
  <%= sync partial: 'list_row', resource: todo, refetch: true %>
<% end %>
<%= sync_new partial: 'list_row', resource: Todo.new, scope: @project, refetch: true %>

Notes

While this approach works very well for the cases it's needed, syncing without refetching should be used unless refetching is absolutely necessary for performance reasons. For example,

A sync update request is triggered on the server for a 'regular' sync'd partial with 100 listening clients:

• number of http requests 1
• number of renders 1, pushed out to all 100 clients via pubsub server.

A sync update request is triggered on the server for a 'refetch' sync'd partial with 100 listening clients:

• number of http requests 100
• number of renders 100, rendering each request in clients session context.

Sync has a custom DependencyTracker::ERBTracker that can handle sync render calls. Because the full partial name is not included, it has to guess the location of your partial based on the name of the resource or collection passed to it. See the tests to see how it works. If it doesn't work for you, you can always use the explicit "Template Dependency" markers.

To enable, add to config/initializers/cache_digests.rb:

require 'action_view/dependency_tracker'

ActionView::DependencyTracker.register_tracker :haml, Sync::ERBTracker
ActionView::DependencyTracker.register_tracker :erb, Sync::ERBTracker

require 'cache_digests/dependency_tracker'

CacheDigests::DependencyTracker.register_tracker :haml, Sync::ERBTracker
CacheDigests::DependencyTracker.register_tracker :erb, Sync::ERBTracker

Note: haml support is limited, but it seems to work in most cases.

Create a thin configuration file config/sync_thin.yml similar to the following:

---
port: 4443
ssl: true
ssl_key_file: /path/to/server.pem
ssl_cert_file: /path/to/certificate_chain.pem
environment: production
rackup: sync.ru

The certificate_chain.pem file should contain your signed certificate, followed by intermediate certificates (if any) and the root certificate of the CA that signed the key.

Next reconfigure the server and adapter_javascript_url in config/sync.yml to look like https://your.hostname.com:4443/faye and https://your.hostname.com:4443/faye/faye.js respectively.

Finally start up Thin from the project root.

thin -C config/sync_thin.yml start

View sync/users/_user_list_row.html.erb

<tr>
  <td><%= link_to user.name, user %></td>
  <td><%= link_to 'Edit', edit_user_path(user) %></td>
  <td><%= link_to 'Destroy', user, method: :delete, remote: true, data: { confirm: 'Are you sure?' } %></td>
</tr>

View users/index.html.erb

<h1>Some Users</h1>
<table>
  <tbody>
    <%= sync partial: 'user_list_row', collection: @users %>
    <%= sync_new partial: 'user_list_row', resource: User.new, direction: :append %>
  </tbody>
</table>

Controller

def UsersController < ApplicationController
  …
  def create
    @user = User.new(user_params)
    if @user.save
      sync_new @user      
    end
    respond_to do |format|
      format.html { redirect_to users_url }
      format.json { head :no_content }
    end
  end

  def update
    @user = User.find(params[:id])
    if user.save
    …
    end

    # Sync updates to any partials listening for this user
    sync_update @user

    redirect_to users_path, notice: "Saved!"
  end

  def destroy
    @user = User.find(params[:id])
    @user.destroy

    # Sync destroy, telling client to remove all dom elements containing this user
    sync_destroy @user

    respond_to do |format|
      format.html { redirect_to users_url }
      format.json { head :no_content }
    end
  end
end