Class: Snapshot

Inherits:
Object show all
Defined in:
lib/mega/snapshot.rb

Overview

:title: Snapshot

A lightweight single-depth object state capture. The #take_snapshot method reads the object’s state, which is generally it’s collection of instance variables, and returns them in a hash. The state can be restored with #apply_snapshot.

Usage

Customer = Struct.new("Customer", :name, :address, :zip)
joe = Customer.new( "Joe Pitare", "1115 Lila Ln.", 47634 )

# simple transactions
joe_snap = joe.take_snapshot
begin
  do_something_with( joe )
rescue
  joe.apply_snapshot( joe_snap )
end

joe_snap[:name]     => "Joe Pitare"
joe_snap[:address]  => "1115 Lila Ln."
joe_snap[:zip]      => 47634

Details

Class Snapshot simply represents a collection of objects from which snapshots were taken via their methods #take_snapshot. It provides methods to add an object to a snapshot (Snapshot#add) as well as to restore all objects of the snapshot to their state stored in the snapshot (method Snapshot#restore).

In Wee, this class is used to backtracking the state of components (or decorations/presenters). Components that want an undo-facility to be implemented (triggered for example by a browsers back-button), have to overwrite the Wee::Component#backtrack_state method.

Author(s)

  • Michael Neumann

Instance Method Summary collapse

Constructor Details

#initialize ⇒ Snapshot

Returns a new instance of Snapshot.



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# File 'lib/mega/snapshot.rb', line 77

def initialize
  @objects = Hash.new
end

Instance Method Details

#add(object) ⇒ Object 



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# File 'lib/mega/snapshot.rb', line 81

def add(object)
  oid = object.object_id
  @objects[oid] = [object, object.take_snapshot] unless @objects.include?(oid) 
end

#restore ⇒ Object 



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# File 'lib/mega/snapshot.rb', line 86

def restore
  @objects.each_value { |object, value| object.restore_snapshot(value) }
end