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 object. Active Model also helps building 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 behaves like an Active Record model.
* Add callbacks and validations like Active Record.
* Add serializers.
* Integrate 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.
### ActiveModel::AttributeMethods
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
```
### ActiveModel::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
```
### ActiveModel::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
```
### ActiveModel::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
# 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 # => "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 # => [nil, "First Name"]
person.last_name_change # => nil
```
### ActiveModel::Validations
`ActiveModel::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
```
### ActiveModel::Naming
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"
### ActiveModel::Model
`ActiveModel::Model` adds the ability to a class to work with Action Pack and
Action View out of box.
```ruby
class EmailContact
include ActiveModel::Model
attr_acessor :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.
### ActiveModel::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 using the `from_json`.
```ruby
json = { name: 'Bob' }.to_json
person = Person.new
person.from_json(json) # => #<Person:0x00000100c773f0 @name="Bob">
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 # => "<?xml version=\"1.0\" encoding=\"UTF-8\"?>\n<person>\n <name nil=\"true\"/>\n</person>\n"
person.name = "Bob"
person.to_xml # => "<?xml version=\"1.0\" encoding=\"UTF-8\"?>\n<person>\n <name>Bob</name>\n</person>\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 using the `from_xml`.
```ruby
xml = { name: 'Bob' }.to_xml
person = Person.new
person.from_xml(xml) # => #<Person:0x00000100c773f0 @name="Bob">
person.name # => "Bob"
```
### 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"
```
### ActiveModel::Lint::Tests
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.
