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Rasna Shakya
Associate software engineer

Overview
What is facade pattern?
Why facade pattern?
Advantage
Drawbacks

Jyaasa : We Design, Build and Develop Products
What is Facade Pattern?
The Facade Pattern is simply a formalization of the idea that if you
cannot avoid complexity, then the next best thing to do is to isolate it, to
keep it from contaminating your whole system” -- Russ Olsen
Facade pattern provides a unified interface to a set of interfaces in a
subsystem.
Facade pattern hides the complexities of the system and provides an
interface to the client

Why facade pattern?

Ruby on rails is built on MVC paradigm.
The problem in rails project, Controller is very weak and a lot of
query and logics are happening on it to prepare data for views.
Although we can use services and decorators for restructuring
data to be more digestible by a view, still its not enough and we
have fat controller.

# app/controllers/chat_rooms_controller.rb
Class ChatRoomsController < ApplicationController
before_filter :set_chat_room, only: :show
def show
@message = @chat_room.messages.new
@chat_message = @chat_room.messages.limit(5)
@unread_message = @chat_room.unread_msg(current_user)
end
private
def set_chat_room
@chat_room = current_user.chat_rooms.find(params[:id])
end
end

A lot of initializations of data and helping objects in
controller

Solution ???

We can use use Facade design pattern to remove that
responsibility of preparing data for the view and create unified
face visible to outside world, also to hide the components
underneath.
Let’s create a new folder in Rails project app/facades and let’s
create our facade PORO class

# app/facades/chat_rooms_facade.rb
Class ChatRoomsFacade
attr_reader :chat_room, current_user
def initialize(chat_room, current_user)
@chat_room = chat_room
@current_user = current_user
end
def unread_message
@unread_message = chat_room.unread_msg(current_user)
end
def new_message
@message = Message.new
end
def chat_message
@chat_message = chat_room.messages.limit(5)
end
end

After moving all of the data preparations to ChatRoomsFacade, that allows us
to simply controller:
# app/controllers/chat_rooms_controller.rb
Class ChatRoomsController < ApplicationController
before_filter :set_chat_room, only: :show
def show
@chat_room = ChatRoomsFacade,new(@chat_room,
current_user)
end
Private
def set_chat_room
@chat_room = current_user.chat_rooms.find(params[:id])
end
end

and use it in the view:
<%= @chat_room.chat_message %>
<%= @chat_room.unread_message %>

Advantage
Facade pattern can be very helpful for simplifying the controllers,
especially if we have rather big project that is still growing.

- Introducing another layer of abstraction to our application
Demerits

Thank you

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Facade pattern in rails

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