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+h2. Active Model Basics
+
+This guide should provide you with all you need to get started using model classes. Active Model allows for Action Pack helpers to interact with non-ActiveRecord models. Active Model also helps building custom ORMs for use outside of the Rails framework.
+
+endprologue.
+
+WARNING. This guide is based on Rails 3.0. Some of the code shown here will not work in earlier versions of Rails.
+
+h3. Introduction
+
+Active Model is a library containing various modules used in developing frameworks that need to interact with the Rails Action Pack library. Active Model provides a known set of interfaces for usage in classes. Some of modules are explained below.  
+
+h4. AttributeMethods
+
+The AttributeMethods module can add custom prefixes and suffixes on methods of a class. It is used by defining the prefixes and suffixes, which methods on the object will use them.
+
+<ruby>
+class Person
+  include ActiveModel::AttributeMethods
+
+  attribute_method_prefix 'reset_'
+  attribute_method_suffix '_highest?'
+  define_attribute_methods 'age'
+
+  attr_accessor :age
+
+private
+  def reset_attribute(attribute)
+    send("#{attribute}=", 0)
+  end
+
+  def attribute_highest?(attribute)
+    send(attribute) > 100 ? true : false
+  end
+  
+end
+
+person = Person.new
+person.age = 110
+person.age_highest?  # true
+person.reset_age     # 0
+person.age_highest?  # false 
+
+</ruby>
+
+h4. Callbacks
+
+Callbacks gives Active Record style callbacks. This provides the ability to define the callbacks and those will run at appropriate time. After defining a callbacks you can wrap with before, after and around custom methods.
+
+<ruby>
+class Person
+  extend ActiveModel::Callbacks
+
+  define_model_callbacks :update
+
+  before_update :reset_me
+
+  def update
+    run_callbacks(:update) do
+      # This will call when we are trying to call update on object.
+    end
+  end
+
+  def reset_me
+    # This method will call when you are calling update on object as a before_update callback as defined.
+  end
+end
+</ruby>
+
+h4. Conversion
+
+If a class defines persisted? and id methods then you can include Conversion module in that class and you can able to call Rails conversion methods to objects of that class.
+
+<ruby>
+class Person
+  include ActiveModel::Conversion
+
+  def persisted?
+    false
+  end
+
+  def id
+    nil
+  end
+end
+
+person = Person.new
+person.to_model == person  #=> true
+person.to_key              #=> nil
+person.to_param            #=> nil
+</ruby>
+
+h4. Dirty
+
+An object becomes dirty when it has gone through one or more changes to its attributes and has not been saved. This gives the ability to check whether an object has been changed or not. It also has attribute based accessor methods. Let's consider a Person class with attributes first_name and last_name
+
+<ruby>
+require 'active_model'
+
+class Person
+  include ActiveModel::Dirty
+  define_attribute_methods :first_name, :last_name
+
+  def first_name
+    @first_name
+  end
+
+  def first_name=(value)
+    first_name_will_change!
+    @first_name = value
+  end
+
+  def last_name
+    @last_name
+  end
+
+  def last_name=(value)
+    last_name_will_change!
+    @last_name = value
+  end
+
+  def save
+    @previously_changed = changes
+  end
+
+end
+</ruby>
+
+h5. Querying object directly for its list of all changed attributes.
+
+<ruby>
+person = Person.new
+person.first_name = "First Name"
+
+person.first_name #=> "First Name"
+person.first_name = "First Name Changed"
+
+person.changed? #=> true
+
+#returns an list of fields arry which all has been changed before saved.
+person.changed #=> ["first_name"]
+
+#returns a hash of the fields that have changed with their original values.
+person.changed_attributes #=> {"first_name" => "First Name Changed"}
+
+#returns a hash of changes, with the attribute names as the keys, and the values will be an array of the old and new value for that field.
+person.changes #=> {"first_name" => ["First Name","First Name Changed"]}
+</ruby>
+
+h5. Attribute based accessor methods
+
+Track whether the particular attribute has been changed or not.
+
+<ruby>
+#attr_name_changed?
+person.first_name #=> "First Name"
+
+#assign some other value to first_name attribute
+person.first_name = "First Name 1"
+
+person.first_name_changed? #=> true
+</ruby>
+
+Track what was the previous value of the attribute.
+
+<ruby>
+#attr_name_was accessor
+person.first_name_was  #=> "First Name"
+</ruby>
+
+Track both previous and current value of the changed attribute. Returns an array if changed, else returns nil.
+
+<ruby>
+#attr_name_change
+person.first_name_change #=> ["First Name", "First Name 1"]
+person.last_name_change #=> nil
+</ruby>
+
+h4. Validations
+
+Validations module adds the ability to class objects to validate them in Active Record style.
+
+<ruby>
+class Person
+  include ActiveModel::Validations
+
+  attr_accessor :name, :email, :token
+  
+  validates :name, :presence => true
+  validates_format_of :email, :with => /\A([^\s]+)((?:[-a-z0-9]\.)[a-z]{2,})\z/i  
+  validates! :token, :presence => true
+  
+end
+
+person = Person.new(:token => "2b1f325")
+person.valid?                        #=> false
+person.name  = 'vishnu'
+person.email  = 'me'
+person.valid?                        #=> false
+person.email = 'me@vishnuatrai.com'
+person.valid?                        #=> true
+person.token = nil
+person.valid?                        #=> raises ActiveModel::StrictValidationFailed
+</ruby>