I have three models User, Activity and ActivityRecord.

class User < ActiveRecord::Base
  # Include default devise modules. Others available are:
  # :token_authenticatable, :confirmable,
  # :lockable, :timeoutable and :omniauthable
  devise :database_authenticatable, :registerable,
         :recoverable, :rememberable, :trackable, :validatable

  # Setup accessible (or protected) attributes for your model
  attr_accessible :first_name, :last_name, :email, :gender, :password, :password_confirmation, :remember_me
  # attr_accessible :title, :body

  has_many :activities 
  has_many :activity_records , :through=> :activities
end

class Activity < ActiveRecord::Base
  attr_accessible :point, :title
  belongs_to :user
  has_many :activity_records
end

class ActivityRecord < ActiveRecord::Base
    attr_accessible :activity_id
    belongs_to :activity

    scope :today, lambda { where("DATE(#{'activity_records'}.created_at) = '#{Date.today.to_s(:db)}'")}
end

I would like to query all activities for a user together with the count for their respective activity records for today. For example, after querying and converting to json format, I would like to have something like below

[
   { 
      id: 23
      title: "jogging",
      point: "5",
      today_activity_records_count: 1,
   },
   { 
      id: 12
      title: "diet dinner",
      point: "2",
      today_activity_records_count: 0,
   },
]

Please kindly guide me how I can achieve that.

Thanks