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 plain Ruby objects. Active Model also helps build custom ORMs for use outside of the Rails framework. After reading this guide, you will be able to add to plain Ruby objects: * The ability to behave like an Active Record model. * Callbacks and validations like Active Record. * Serializers. * Integration with the Rails internationalization (i18n) framework. -------------------------------------------------------------------------------- Introduction ------------ Active Model is a library containing various modules used in developing classes that need some features present on Active Record. Some of these modules are explained below. ### Attribute Methods The `ActiveModel::AttributeMethods` module can add custom prefixes and suffixes on methods of a class. It is used by defining the prefixes and suffixes and 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 end end person = Person.new person.age = 110 person.age_highest? # => true person.reset_age # => 0 person.age_highest? # => false ``` ### Callbacks `ActiveModel::Callbacks` gives Active Record style callbacks. This provides an ability to define callbacks which run at appropriate times. After defining callbacks, you can wrap them 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 method is called when update is called on an object. end end def reset_me # This method is called when update is called on an object as a before_update callback is defined. end end ``` ### Conversion If a class defines `persisted?` and `id` methods, then you can include the `ActiveModel::Conversion` module in that class and call the Rails conversion methods on 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. `ActiveModel::Dirty` 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 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 # do save work... changes_applied end end ``` #### Querying object directly for its list of all changed attributes. ```ruby person = Person.new person.changed? # => false person.first_name = "First Name" person.first_name # => "First Name" # returns if any attribute has changed. person.changed? # => true # returns a list of attributes that have changed before saving. person.changed # => ["first_name"] # returns a hash of the attributes that have changed with their original values. person.changed_attributes # => {"first_name"=>nil} # 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"=>[nil, "First Name"]} ``` #### Attribute based accessor methods Track whether the particular attribute has been changed or not. ```ruby # attr_name_changed? person.first_name # => "First Name" person.first_name_changed? # => true ``` Track what was the previous value of the attribute. ```ruby # attr_name_was accessor person.first_name_was # => nil ``` 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 # => [nil, "First Name"] person.last_name_change # => nil ``` ### Validations `ActiveModel::Validations` module adds the ability to validate class objects like in Active Record. ```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 person.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 ``` ### Naming `ActiveModel::Naming` adds a number of class methods which make the naming and routing easier to manage. The module defines the `model_name` class method which will define a number of accessors using some `ActiveSupport::Inflector` methods. ```ruby class Person extend ActiveModel::Naming end Person.model_name.name # => "Person" Person.model_name.singular # => "person" Person.model_name.plural # => "people" Person.model_name.element # => "person" Person.model_name.human # => "Person" Person.model_name.collection # => "people" Person.model_name.param_key # => "person" Person.model_name.i18n_key # => :person Person.model_name.route_key # => "people" Person.model_name.singular_route_key # => "person" ``` ### Model `ActiveModel::Model` adds the ability to a class to work with Action Pack and Action View right out of the box. ```ruby class EmailContact include ActiveModel::Model attr_accessor :name, :email, :message validates :name, :email, :message, presence: true def deliver if valid? # deliver email end end end ``` When including `ActiveModel::Model` you get some features like: - model name instrospection - conversions - translations - validations It also gives you the ability to initialize an object with a hash of attributes, much like any Active Record object. ```ruby email_contact = EmailContact.new(name: 'David', email: 'david@example.com', message: 'Hello World') email_contact.name # => 'David' email_contact.email # => 'david@example.com' email_contact.valid? # => true email_contact.persisted? # => false ``` Any class that includes `ActiveModel::Model` can be used with `form_for`, `render` and any other Action View helper methods, just like Active Record objects. ### Serialization `ActiveModel::Serialization` provides a basic serialization for your object. You need to declare an attributes hash which contains the attributes you want to serialize. Attributes must be strings, not symbols. ```ruby class Person include ActiveModel::Serialization attr_accessor :name def attributes {'name' => nil} end end ``` Now you can access a serialized hash of your object using the `serializable_hash`. ```ruby person = Person.new person.serializable_hash # => {"name"=>nil} person.name = "Bob" person.serializable_hash # => {"name"=>"Bob"} ``` #### ActiveModel::Serializers Rails provides two serializers `ActiveModel::Serializers::JSON` and `ActiveModel::Serializers::Xml`. Both of these modules automatically include the `ActiveModel::Serialization`. ##### ActiveModel::Serializers::JSON To use the `ActiveModel::Serializers::JSON` you only need to change from `ActiveModel::Serialization` to `ActiveModel::Serializers::JSON`. ```ruby class Person include ActiveModel::Serializers::JSON attr_accessor :name def attributes {'name' => nil} end end ``` With the `as_json` you have a hash representing the model. ```ruby person = Person.new person.as_json # => {"name"=>nil} person.name = "Bob" person.as_json # => {"name"=>"Bob"} ``` From a JSON string you define the attributes of the model. You need to have the `attributes=` method defined on your class: ```ruby class Person include ActiveModel::Serializers::JSON attr_accessor :name def attributes=(hash) hash.each do |key, value| send("#{key}=", value) end end def attributes {'name' => nil} end end ``` Now it is possible to create an instance of person and set the attributes using `from_json`. ```ruby json = { name: 'Bob' }.to_json person = Person.new person.from_json(json) # => # person.name # => "Bob" ``` ##### ActiveModel::Serializers::Xml To use the `ActiveModel::Serializers::Xml` you only need to change from `ActiveModel::Serialization` to `ActiveModel::Serializers::Xml`. ```ruby class Person include ActiveModel::Serializers::Xml attr_accessor :name def attributes {'name' => nil} end end ``` With the `to_xml` you have a XML representing the model. ```ruby person = Person.new person.to_xml # => "\n\n \n\n" person.name = "Bob" person.to_xml # => "\n\n Bob\n\n" ``` From a XML string you define the attributes of the model. You need to have the `attributes=` method defined on your class: ```ruby class Person include ActiveModel::Serializers::Xml attr_accessor :name def attributes=(hash) hash.each do |key, value| send("#{key}=", value) end end def attributes {'name' => nil} end end ``` Now it is possible to create an instance of person and set the attributes using `from_xml`. ```ruby xml = { name: 'Bob' }.to_xml person = Person.new person.from_xml(xml) # => # person.name # => "Bob" ``` ### Translation `ActiveModel::Translation` provides integration between your object and the Rails internationalization (i18n) framework. ```ruby class Person extend ActiveModel::Translation end ``` With the `human_attribute_name` you can transform attribute names into a more human format. The human format is defined in your locale file. * config/locales/app.pt-BR.yml ```yml pt-BR: activemodel: attributes: person: name: 'Nome' ``` ```ruby Person.human_attribute_name('name') # => "Nome" ``` ### Lint Tests `ActiveModel::Lint::Tests` allow you to test whether an object is compliant with the Active Model API. * app/models/person.rb ```ruby class Person include ActiveModel::Model end ``` * test/models/person_test.rb ```ruby require 'test_helper' class PersonTest < ActiveSupport::TestCase include ActiveModel::Lint::Tests def setup @model = Person.new end end ``` ```bash $ rake test Run options: --seed 14596 # Running: ...... Finished in 0.024899s, 240.9735 runs/s, 1204.8677 assertions/s. 6 runs, 30 assertions, 0 failures, 0 errors, 0 skips ``` An object is not required to implement all APIs in order to work with Action Pack. This module only intends to provide guidance in case you want all features out of the box.