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1 What is Active Model?

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Active Model is a library containing various modules used in developingclasses that need some features present on Active Record.Some of these modules are explained below.

1.1 Attribute Methods

The ActiveModel::AttributeMethods module can add custom prefixes and suffixeson methods of a class. It is used by defining the prefixes and suffixes andwhich methods on the object will use them.

1.2 Callbacks

ActiveModel::Callbacks gives Active Record style callbacks. This provides anability to define callbacks which run at appropriate times.After defining callbacks, you can wrap them with before, after, and aroundcustom methods.

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1.3 Conversion

If a class defines persisted? and id methods, then you can include theActiveModel::Conversion module in that class, and call the Rails conversionmethods on objects of that class.

1.4 Dirty

An object becomes dirty when it has gone through one or more changes to itsattributes and has not been saved. ActiveModel::Dirty gives the ability tocheck whether an object has been changed or not. It also has attribute basedaccessor methods. Let's consider a Person class with attributes first_nameand last_name:

1.4.1 Querying object directly for its list of all changed attributes.

1.4.2 Attribute based accessor methods

Track whether the particular attribute has been changed or not.

Track the previous value of the attribute.

Track both previous and current value of the changed attribute. Returns an arrayif changed, otherwise returns nil.

1.5 Validations

The ActiveModel::Validations module adds the ability to validate objectslike in Active Record.

1.6 Naming

ActiveModel::Naming adds a number of class methods which make naming and routingeasier to manage. The module defines the model_name class method whichwill define a number of accessors using some ActiveSupport::Inflector methods.

1.7 Model

ActiveModel::Model adds the ability for a class to work with Action Pack andAction View right out of the box.

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.

Any class that includes ActiveModel::Model can be used with form_with,render and any other Action View helper methods, just like Active Recordobjects.

1.8 Serialization

ActiveModel::Serialization provides basic serialization for your object.You need to declare an attributes Hash which contains the attributes you want toserialize. Attributes must be strings, not symbols.

Now you can access a serialized Hash of your object using the serializable_hash method.

1.8.1 ActiveModel::Serializers

Active Model also provides the ActiveModel::Serializers::JSON modulefor JSON serializing / deserializing. This module automatically includes thepreviously discussed ActiveModel::Serialization module.

1.8.1.1 ActiveModel::Serializers::JSON

To use ActiveModel::Serializers::JSON you only need to change themodule you are including from ActiveModel::Serialization to ActiveModel::Serializers::JSON.

The as_json method, similar to serializable_hash, provides a Hash representingthe model.

You can also define the attributes for a model from a JSON string.However, you need to define the attributes= method on your class:

Now it is possible to create an instance of Person and set attributes using from_json.

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1.9 Translation

ActiveModel::Translation provides integration between your object and the Railsinternationalization (i18n) framework.

With the human_attribute_name method, you can transform attribute names into amore human-readable format. The human-readable format is defined in your locale file(s).

• config/locales/app.pt-BR.yml

1.10 Lint Tests

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ActiveModel::Lint::Tests allows you to test whether an object is compliant withthe Active Model API.

• app/models/person.rb

  class Person include ActiveModel::Modelend

• test/models/person_test.rb

  require 'test_helper'class PersonTest < ActiveSupport::TestCase include ActiveModel::Lint::Tests setup do @model = Person.new endend

An object is not required to implement all APIs in order to work withAction Pack. This module only intends to provide guidance in case you want allfeatures out of the box.

1.11 SecurePassword

ActiveModel::SecurePassword provides a way to securely store anypassword in an encrypted form. When you include this module, ahas_secure_password class method is provided which definesa password accessor with certain validations on it by default.

1.11.1 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 XXX_digest.Where XXX is the attribute name of your desired password.The following validations are added automatically:

1. Password should be present.
2. Password should be equal to its confirmation (provided XXX_confirmation is passed along).
3. The maximum length of a password is 72 (required by bcrypt on which ActiveModel::SecurePassword depends)

1.11.2 Examples

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