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.

Methods

add
new
restore

Classes and Modules

Class Snapshot::ValueHolder

Public Class methods

new()

[ show source ]

# File lib/more/facets/snapshot.rb, line 109
  def initialize
    @objects = Hash.new
  end

Public Instance methods

add(object)

[ show source ]

# File lib/more/facets/snapshot.rb, line 113
  def add(object)
    oid = object.object_id
    @objects[oid] = [object, object.take_snapshot] unless @objects.include?(oid)
  end

restore()

[ show source ]

# File lib/more/facets/snapshot.rb, line 118
  def restore
    @objects.each_value do
      |object, value| object.restore_snapshot(value)
    end
  end