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-Active Record models. Active Model also helps building custom ORMs for use outside of the Rails framework. After reading this guide, you will know: -------------------------------------------------------------------------------- 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. ### 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 ``` ### 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 ``` ### 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 ``` ### 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 ``` #### 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"]} ``` #### 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 ``` Track what was the previous value of the attribute. ```ruby #attr_name_was accessor person.first_name_was #=> "First Name" ``` 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 ``` ### 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 ```