Acts as state machine (aasm)

A finite-state machine (FSM) is based on the concept of an object being in a particular state and then transitioning to other states based on certain events. Let's take the example of reserving a book. The states that the reservation can be in are available, booked, and late. For this example, the reservation can transition to these states in any of the following ways:

• All books have a single reservation each

• The default status of a reservation is available

• A customer can reserve a book if it's available

• A customer can return a book if it's booked or it's late

• A book is delayed if it's reserved for more than the default seven days

To use the state machine, we need to add the aasm gem into Gemfile as follows:

class Reservation
  include Mongoid::Document
  include AASM

  field :aasm_state, type: String
  field :booked_on, type: Date
  field booked_by, type: String
  field :returned_on, type: Date
  field :days_reserved, type: Integer, default: 7
  
  belongs_to :book...