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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 know:
- How an Active Record model behaves.
- How Callbacks and validations work.
- How serializers work.
- 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.
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.
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.
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
:
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.
person = Person.new
person.changed? # => false
person.first_name = "First Name"
person.first_name # => "First Name"
# returns true if any of the attributes have unsaved changes, false otherwise.
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.
# attr_name_changed?
person.first_name # => "First Name"
person.first_name_changed? # => true
Track what was the previous value of the attribute.
# 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.
# attr_name_change
person.first_name_change # => [nil, "First Name"]
person.last_name_change # => nil
Validations
The ActiveModel::Validations
module adds the ability to validate class objects
like in Active Record.
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.
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.
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 introspection
- conversions
- translations
- validations
It also gives you the ability to initialize an object with a hash of attributes, much like any Active Record object.
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 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.
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
.
person = Person.new
person.serializable_hash # => {"name"=>nil}
person.name = "Bob"
person.serializable_hash # => {"name"=>"Bob"}
ActiveModel::Serializers
Rails provides an ActiveModel::Serializers::JSON
serializer.
This module 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
.
class Person
include ActiveModel::Serializers::JSON
attr_accessor :name
def attributes
{'name' => nil}
end
end
With the as_json
method you have a hash representing the model.
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:
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
.
json = { name: 'Bob' }.to_json
person = Person.new
person.from_json(json) # => #<Person:0x00000100c773f0 @name="Bob">
person.name # => "Bob"
Translation
ActiveModel::Translation
provides integration between your object and the Rails
internationalization (i18n) framework.
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
pt-BR: activemodel: attributes: person: name: 'Nome'
Person.human_attribute_name('name') # => "Nome"
Lint Tests
ActiveModel::Lint::Tests
allows you to test whether an object is compliant with
the Active Model API.
-
app/models/person.rb
class Person include ActiveModel::Model end
-
test/models/person_test.rb
require 'test_helper' class PersonTest < ActiveSupport::TestCase include ActiveModel::Lint::Tests setup do @model = Person.new end end
$ rails 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.
SecurePassword
ActiveModel::SecurePassword
provides a way to securely store any
password in an encrypted form. On including this module, a
has_secure_password
class method is provided which defines
an accessor named password
with certain validations on it.
Requirements
ActiveModel::SecurePassword
depends on bcrypt
,
so include this gem in your Gemfile to use ActiveModel::SecurePassword
correctly.
In order to make this work, the model must have an accessor named password_digest
.
The has_secure_password
will add the following validations on the password
accessor:
- Password should be present.
- Password should be equal to its confirmation.
- The maximum length of a password is 72 (required by
bcrypt
on which ActiveModel::SecurePassword depends)
Examples
class Person
include ActiveModel::SecurePassword
has_secure_password
attr_accessor :password_digest
end
person = Person.new
# When password is blank.
person.valid? # => false
# When the confirmation doesn't match the password.
person.password = 'aditya'
person.password_confirmation = 'nomatch'
person.valid? # => false
# When the length of password exceeds 72.
person.password = person.password_confirmation = 'a' * 100
person.valid? # => false
# When all validations are passed.
person.password = person.password_confirmation = 'aditya'
person.valid? # => true