finish old active model post

Author: tonywok

_posts/2020-07-09-a-peek-behind-active-model.md

@@ -0,0 +1,190 @@
+---
+layout: post
+author: Tony Schneider
+title : A Peek Behind ActiveModel::Model
+date  : 2020-06-24
+tags  : software
+---
+
+I find myself using `ActiveModel::Model` quite a bit.
+
+It’s a quick and easy way to supercharge your ruby objects with all kinds of functionality to make them compatible with `ActionView` (forms) and `ActionPack` (routing).
+
+Aside from this compatibility, it makes your ruby object _feel_ a bit more like an `ActiveRecord` object.
+In fact, much of ActiveModel was extracted from ActiveRecord during the Rails 3 refactors of old.
+
+I often reach for it when making form objects using [The Command Pattern]({% post_url 2020-06-24-the-command-pattern %}).
+
+```ruby
+
+class CancelSubscription
+  include ActiveModel::Model
+
+  validates :subscription, :presence => true
+  validates :cancellation_date, :presence => true
+
+  attr_accessor :subscription, :cancellation_date
+
+  def execute
+    # logic for canceling a subscription
+  end
+end
+
+form = CancelSubscription.new(
+  subscription: subscription,
+  cancellation_date: cancellation_date
+)
+form.valid? # => true / false
+form.execute # => subscription cancelled!
+```
+
+Let’s take a closer look at `ActiveModel::Model` to see what it’s doing for us behind the scenes.
+
+It implements the following methods:
+
+* `initialize`
+* `persisted?`
+
+It includes these modules:
+
+* `ActiveModel::AttributeAssignment`
+* `ActiveModel::Validations`
+* `ActiveModel::Conversion`
+
+It is extended with these modules:
+
+* `ActiveModel::Naming`
+* `ActiveModel::Translation`
+
+Each of these modules serves a purpose, but can also be used in isolation.
+
+### ActiveModel::AttributeAssignment
+
+This module is included for the sole purpose of making this work:
+
+```ruby
+form = CancelSubscription.new
+form.assign_attributes(subscription: subscription, cancellation_date: cancellation_date)
+form.subscription # => subscription
+form.cancellation_date # => cancellation_date
+```
+
+The `ActiveModel::Model#initialize` method uses this functionality to implement the `ActiveRecord`-like constructor interface:
+
+```ruby
+form = CancelSubscription.new(
+  subscription: subscription,
+  cancellation_date: cancellation_date
+)
+```
+
+It iterates over the hash of parameters passed into the constructor, assigning values using the setters you’re expected to have defined via `attr_accessor`.
+
+If a setter hasn’t been defined, it will raise an `UnknownAttributeError`.
+
+### ActiveModel::Validation
+
+Validations define a rich class-level DSL for expressing what your model considers “valid”.
+
+As a result, instances of the model gain a handful of methods allowing you to inquire about the validity (e.g `model.valid?`).
+
+Once `model.valid?` has been called, it populates `model.errors` with error messages indicating that your model has attribute values that the classes' validators consider _invalid_.
+
+The `model.errors` method returns an instance of `ActiveModel::Error`, which is a hash-like object for accessing attribute errors and messages.
+
+This is extremely useful, especially when constructing models from user-provided data or data from programmer provided configuration.
+
+```ruby
+form = CancelSubscription.new
+form.valid? # => false
+form.errors.full_messages # => ["subscription can't be blank", "cancellation_date can't be blank"]
+```
+
+`Validations` comes with a whole sweet of built-in validations - some of which you've probably used with `ActiveRecord`.
+It also provides an easy way to define ad hoc validations via `validate` as well as a full-featured `Validator` interface for more re-usable validations.
+
+### ActiveModel::Translation
+
+As you may have guessed, this module is the glue between your model and the Rails i18n internationalization framework.
+
+This module exposes a class level interface for defining translations that correspond to your attributes a la: 
+
+```ruby
+CancelSubscription.human_attribute_name(:cancellation_date) 
+# => Fecha de cancelación
+```
+
+Also, it allows you to define an `i18n_scope` method to control the expected i18n key path for your model's translations.
+
+### ActiveModel::Naming
+
+Extending this module gives you a class method called `model_name` that returns an instance of `ActiveModel::Name`.
+Also, instances of your class will delegate the `model_name` to your class.
+
+`ActiveModel::Name` implements much of what powers Rails' "convention over configuration" by taking the name of your class and hooking it up with `ActiveSupport::Inflector`.
+
+Understanding how this module works really pulls the curtain back from the infamous "Rails' Magic".
+
+### ActiveModel::Conversion
+
+Continuing the "Rails Magic" misnomer, `Conversion` is another common source of confusion.
+
+It does the job of extracting data from your model to further inform rails conventions such as:
+
+* Finding partial paths via `to_partial_path`
+* Constructing URLs via `to_param`
+
+Worth noting that by default `to_param` will return `nil`  unless your model is `persisted?`.
+However, you can certainly implement it yourself to your liking.
+
+## Putting It All Together
+
+Hopefully, now you see that `ActiveModel::Model` is nothing more than a series of modules meant to make your Ruby objects work more seamlessly with the Rails framework.
+
+Once you realize what they do, it's pretty easy to customize them or omit them entirely to suit your needs.
+
+For example, a few things that bother me about `ActiveModel::Model`:
+
+1. I like to utilize keword args to fail fast.
+1. I dislike having to call super if I need to modify the constructor.
+1. I don't like that calling code has access to setters from `attr_accessor`.
+
+```ruby
+module FormModel
+  extend ActiveSupport::Concern
+
+  include ActiveModel::Validations
+  include ActiveModel::Conversion
+
+  included do
+    extend ActiveModel::Naming
+    extend ActiveModel::Translation
+  end
+
+  def persisted?
+    false
+  end
+end
+```
+
+Now I can do something like this, opting out of the `AttributeAssignment` behavior I don't care for:
+
+```ruby
+class CancelSubscription
+  include FormModel
+
+  validates :subscription, :presence => true
+  validates :cancellation_date, :presence => true
+
+  attr_reader :subscription, :cancellation_date
+
+  def initialize(subscription:, cancellation_date: Time.zone.today)
+    @subscription = subscription
+    @cancellation_date = cancellation_date
+  end
+
+  def execute
+    # logic for canceling a subscription
+  end
+end
+```

_site/index.html

@@ -45,6 +45,12 @@ <h2>
 <img class="emoji" title=":computer:" alt=":computer:" src="https://github.githubassets.com/images/icons/emoji/unicode/1f4bb.png" height="20" width="20"> Software</h2>
     <ul>
 <li>
+<span class="post-meta mono">2020-06-24</span>
+        <a href="/2020/06/24/a-peek-behind-active-model.html">
+          A Peek Behind ActiveModel::Model
+        </a>
+</li>
+<li>
 <span class="post-meta mono">2020-06-24</span>
         <a href="/2020/06/24/the-command-pattern.html">
           The Command Pattern