Activity Feed pattern

_activity_feed.html.haml

%ul

  - activities.each do |activity|
    %li
      .activity{ data: { role: activity.activity_type } }
        = render_activity activity

_bid_offered.html.haml

#{user_path(bid.user)} offered a bid of #{bid.amount.format} for your job, #{bid_path(bid)}.

activity.rb

class Activity < ActiveRecord::Base
  belongs_to :subject, polymorphic: true
  belongs_to :user
end

application_helper.rb

module ApplicationHelper
  def render_activity(activity, user = current_user)
    activity_type = activity.activity_type
    subject = activity.subject
    partial = "activities/#{activity_type}"
    subject_type = activity.subject_type.underscore.to_sym
    render partial, subject_type => subject
  end
end

bid_offered_job.rb

class BidOfferedJob < Struct.new(:bid_id)
  PRIORITY = 1

  def self.enqueue(bid)
    Delayed::Job.enqueue new(bid.id), priority: PRIORITY
  end

  def perform
    Mailer.bid_offered(owner, bid).deliver
    Activity.create activity_type: 'bid_offered', subject: bid, user: owner
  end

  private

  def bid
    Bid.find bid_id
  end

  def owner
    bid.job.owner
  end
end

create_activities.rb

class RenameActivityNotifications < ActiveRecord::Migration
  def up
    create_table :activities do |t|
      t.timestamps null: false
      t.integer :user_id, null: false
      t.integer :subject_id, null: false
      t.string :subject_type, null: false
      t.string :activity_type, null: false
    end

    add_index :activities, :user_id
    add_index :activities, :subject_id
    add_index :activities, :subject_type
  end

  def down
    drop_table :activities
  end
end