From 4a4cb658f63e1f567f0ce720904511c7287e7e23 Mon Sep 17 00:00:00 2001
From: "Rico Sta. Cruz" <rstacruz@users.noreply.github.com>
Date: Sun, 3 Sep 2017 02:57:25 +0800
Subject: [PATCH] Related posts: fix up gutters

---
 _includes/2017/related-posts.html             |   2 +-
 ...ated-posts.scss => related-post-list.scss} |  18 -
 _sass/2017/components/related-posts-area.scss |  17 +
 .../components/related-posts-section.scss     |  16 +-
 _sass/2017/style.scss                         |   3 +-
 rails-models.md                               | 578 ++++++++++++------
 6 files changed, 409 insertions(+), 225 deletions(-)
 rename _sass/2017/components/{related-posts.scss => related-post-list.scss} (57%)
 create mode 100644 _sass/2017/components/related-posts-area.scss

diff --git a/_includes/2017/related-posts.html b/_includes/2017/related-posts.html
index 40696c238..4e9dd68ef 100644
--- a/_includes/2017/related-posts.html
+++ b/_includes/2017/related-posts.html
@@ -10,7 +10,7 @@
   | where_exp: "page", "page.deprecated != true"
   | sort: "weight", "last"
 %}
-<footer class='related-posts' id='related'>
+<footer class='related-posts-area' id='related'>
   <div class='container'>
     <div class='related-posts-section'>
       <div class='callout'>
diff --git a/_sass/2017/components/related-posts.scss b/_sass/2017/components/related-post-list.scss
similarity index 57%
rename from _sass/2017/components/related-posts.scss
rename to _sass/2017/components/related-post-list.scss
index b828fabd2..e889bb391 100644
--- a/_sass/2017/components/related-posts.scss
+++ b/_sass/2017/components/related-post-list.scss
@@ -1,21 +1,3 @@
-/*
- * Related posts
- */
-
-.related-posts {
-  & {
-    @include section-with-container;
-    padding-top: 16px;
-    padding-bottom: 16px;
-    background: $gray-bg;
-  }
-
-  @media (min-width: 481px) {
-    padding-top: 64px;
-    padding-bottom: 64px;
-  }
-}
-
 .related-post-list {
   &,
   & > li {
diff --git a/_sass/2017/components/related-posts-area.scss b/_sass/2017/components/related-posts-area.scss
new file mode 100644
index 000000000..4a61127ea
--- /dev/null
+++ b/_sass/2017/components/related-posts-area.scss
@@ -0,0 +1,17 @@
+/*
+ * Related posts
+ */
+
+.related-posts-area {
+  & {
+    @include section-with-container;
+    padding-top: 16px;
+    padding-bottom: 16px;
+    background: $gray-bg;
+  }
+
+  @media (min-width: 481px) {
+    padding-top: 64px;
+    padding-bottom: 64px;
+  }
+}
diff --git a/_sass/2017/components/related-posts-section.scss b/_sass/2017/components/related-posts-section.scss
index a6d09ff09..dd42b85d7 100644
--- a/_sass/2017/components/related-posts-section.scss
+++ b/_sass/2017/components/related-posts-section.scss
@@ -6,13 +6,15 @@
 .related-posts-section {
   & {
     display: flex;
-    margin-left: -16px;
-    margin-right: -16px;
+    @include section-gutter(margin-left, $multiplier: -1);
+    @include section-gutter(margin-right, $multiplier: -1);
   }
 
   & > .callout,
   & > .group {
-    margin: 0 16px;
+    margin: 0;
+    @include section-gutter(margin-left);
+    @include section-gutter(margin-right);
   }
 
   & > .callout {
@@ -39,8 +41,8 @@
 
     & > .callout,
     & > .group {
-      margin-top: 16px;
-      margin-bottom: 16px;
+      @include section-gutter(margin-top);
+      @include section-gutter(margin-bottom);
       flex: 1 1 100%;
     }
   }
@@ -54,8 +56,8 @@
 
       & > .callout,
       & > .group {
-        margin-top: 16px;
-        margin-bottom: 16px;
+        @include section-gutter(margin-top);
+        @include section-gutter(margin-bottom);
         flex: 1 1 100%;
       }
 
diff --git a/_sass/2017/style.scss b/_sass/2017/style.scss
index 946b982f9..653cbfe2d 100644
--- a/_sass/2017/style.scss
+++ b/_sass/2017/style.scss
@@ -32,10 +32,11 @@
 @import './components/pages-list';
 @import './components/pre-footer';
 @import './components/push-button';
-@import './components/related-posts';
+@import './components/related-posts-area';
 @import './components/related-posts-callout';
 @import './components/related-posts-group';
 @import './components/related-posts-section';
+@import './components/related-post-list';
 @import './components/related-post-item';
 @import './components/search-box';
 @import './components/search-footer';
diff --git a/rails-models.md b/rails-models.md
index 3ac3e5458..98faf3c56 100644
--- a/rails-models.md
+++ b/rails-models.md
@@ -1,112 +1,161 @@
 ---
-title: Models
+title: Rails models
 category: Rails
+layout: 2017/sheet
 ---
 
-### [QueryMethods](http://devdocs.io/rails/activerecord/querymethods)
+Generating
+----------
 
-```rb
+### Generating
+
+    $ rails g model User
+
+Using models
+------------
+
+### Query methods
+
+```ruby
 items = Model
   .where(first_name: 'Harvey')
   .where('id = 3')
   .where('id = ?', 3)
+```
 
+```ruby
   .order(:title)
   .order(title: :desc)
   .order("title DESC")
+```
 
+```ruby
   .reorder(:title)  # discards other .order's
   .rewhere(...)     # discards other .where's
+```
 
+```ruby
   .limit(2)
   .offset(1)
   .uniq
 ```
 
-Advanced:
+See: [QueryMethods](http://devdocs.io/rails/activerecord/querymethods)
 
-```rb
+### Advanced query methods
+
+```ruby
+items = Model
   .select(:id)
   .select([:id, :name])
+```
 
+```ruby
   .group(:name)   # GROUP BY name
   .group('name AS grouped_name, age')
   .having('SUM(price) > 30')  # needs to be chained with .group
-
-  .includes(:user)
-  .includes(user: [:articles])
-
-  .references(:posts)
-  # .where("posts.name = 'foo'").references(:posts)
 ```
 
-### [FinderMethods](http://devdocs.io/rails/activerecord/findermethods)
+```ruby
+  .includes(:user)
+  .includes(user: [:articles])
+```
 
-```rb
+```ruby
+  .references(:posts)
+  # aka: .where("posts.name = 'foo'").references(:posts)
+```
+
+### Finder methods
+
+```ruby
 item = Model.find(id)
 item = Model.find_by_email(email)
 item = Model.where(email: email).first
+```
 
+```ruby
 Model
   .exists?(5)
   .exists?(name: "David")
+```
 
+```ruby
   .first
   .last
   .find_nth(4, [offset])
 ```
 
-### [Persistence](http://devdocs.io/rails/activerecord/persistence)
+See: [FinderMethods](http://devdocs.io/rails/activerecord/findermethods)
 
-```rb
+### Persistence
+
+```ruby
 item.new_record?
 item.persisted?
 item.destroyed?
 
 item.serialize_hash
+```
 
+```ruby
 item.save
 item.save!      # Same as above, but raises an Exception
+```
 
+```ruby
 item.update  name: 'John'  # Saves immediately
 item.update! name: 'John'
+```
 
-
+```ruby
 item.update_column  :name, 'John'  # skips validations and callbacks
 item.update_columns  name: 'John'
 item.update_columns! name: 'John'
+```
 
+```ruby
 item.touch                 # updates :updated_at
 item.touch :published_at
+```
 
+```ruby
 item.destroy
 item.delete  # skips callbacks
 ```
 
-```rb
+```ruby
 Model.create     # Same an #new then #save
 Model.create!    # Same as above, but raises an Exception
 ```
 
-### [AttributeAssignment](http://devdocs.io/rails/activerecord/attributeassignment)
+See: [Persistence](http://devdocs.io/rails/activerecord/persistence)
 
-```rb
+### Attribute Assignment
+
+```ruby
 item.attributes                      # #<Hash>
+```
 
+```ruby
 item.attributes = { name: 'John' }   # Merges attributes in. Doesn't save.
 item.assign_attributes name: 'John'  # Same as above
 ```
 
-### [Dirty](http://devdocs.io/rails/activemodel/dirty)
+See: [AttributeAssignment](http://devdocs.io/rails/activerecord/attributeassignment)
 
-```rb
+### Dirty
+
+```ruby
 item.changed?
 item.changed             # ['name']
 item.changed_attributes  # { 'name' => 'Bob' } - original values
 item.changes             # { 'name' => ['Bob', 'Robert'] }
 item.previous_changes    # available after #save
 item.restore_attributes
+```
 
+```ruby
 item.name = 'Robert'
 item.name_was         # 'Bob'
 item.name_change      # [ 'Bob', 'Robert' ]
@@ -114,224 +163,318 @@ item.name_changed?    # true
 item.name_changed?(from: 'Bob', to: 'Robert')
 ```
 
-### [Validations](http://devdocs.io/rails/activerecord/validations)
+See: [Dirty](http://devdocs.io/rails/activemodel/dirty)
 
-```rb
+### Validations
+
+```ruby
 item.valid?
 item.invalid?
 ```
 
-### [Calculations](http://devdocs.io/rails/activerecord/calculations)
+See: [Validations](http://devdocs.io/rails/activerecord/validations)
 
-```rb
+### Calculations
+
+```ruby
 Person.count
 Person.count(:age)    # counts non-nil's
+```
 
+```ruby
 Person.average(:age)
 Person.maximum(:age)
 Person.minimum(:age)
 Person.sum('2 * age')
+```
 
+```ruby
 Person.calculate(:count, :all)
 ```
 
 Advanced:
 
-```
+```ruby
 Person.distinct.count
 Person.group(:city).count
 ```
 
-Generating
-----------
+See: [Calculations](http://devdocs.io/rails/activerecord/calculations)
 
-    $ rails g model User
+### Dynamic attribute-based finders
+
+Given a field called `name`:
+{: .-setup}
+
+```ruby
+# Returns one record
+Person.find_by_name(name)
+Person.find_last_by_name(name)
+Person.find_or_create_by_name(name)
+Person.find_or_initialize_by_name(name)
+```
+
+```ruby
+# Returns a list of records
+Person.find_all_by_name(name)
+```
+
+```ruby
+# Add a bang to make it raise an exception
+Person.find_by_name!(name)
+```
+
+```ruby
+# You may use `scoped` instead of `find`
+Person.scoped_by_user_name
+```
 
 Associations
 ------------
 
-    belongs_to
-    has_one
-    has_many
-    has_many :through
-    has_one :through
-    has_and_belongs_to_many
+### Associations
+
+- `belongs_to`
+- `has_one`
+- `has_many`
+- `has_many :through`
+- `has_one :through`
+- `has_and_belongs_to_many`
 
 ### Has many
 
-    belongs_to :parent, :foreign_key => 'parent_id' class_name: 'Folder'
-    has_many :folders, :foreign_key => 'parent_id', class_name: 'Folder'
+```ruby
+belongs_to :parent, :foreign_key => 'parent_id' class_name: 'Folder'
+has_many :folders, :foreign_key => 'parent_id', class_name: 'Folder'
 
-    has_many :comments,    :order      => "posted_on"
-    has_many :comments,    :include    => :author
-    has_many :people,      :class_name => "Person"
-    has_many :people,      :conditions => "deleted = 0"
-    has_many :tracks,      :order      => "position"
-    has_many :comments,    :dependent  => :nullify
-    has_many :comments,    :dependent  => :destroy
-    has_many :tags,        :as         => :taggable
-    has_many :reports,     :readonly   => true
-    has_many :subscribers, :through    => :subscriptions, class_name: "User", :source => :user
-    has_many :subscribers, :finder_sql =>
-        'SELECT DISTINCT people.* ' +
-        'FROM people p, post_subscriptions ps ' +
-        'WHERE ps.post_id = #{id} AND ps.person_id = p.id ' +
-        'ORDER BY p.first_name'
+has_many :comments,    :order      => "posted_on"
+has_many :comments,    :include    => :author
+has_many :people,      :class_name => "Person"
+has_many :people,      :conditions => "deleted = 0"
+has_many :tracks,      :order      => "position"
+has_many :comments,    :dependent  => :nullify
+has_many :comments,    :dependent  => :destroy
+has_many :tags,        :as         => :taggable
+has_many :reports,     :readonly   => true
+has_many :subscribers, :through    => :subscriptions, class_name: "User", :source => :user
+has_many :subscribers, :finder_sql =>
+    'SELECT DISTINCT people.* ' +
+    'FROM people p, post_subscriptions ps ' +
+    'WHERE ps.post_id = #{id} AND ps.person_id = p.id ' +
+    'ORDER BY p.first_name'
+```
 
 ### belongs to
 
-    belongs_to :author,
-      :dependent      => :destroy    # or :delete
+```ruby
+belongs_to :author,
+  :dependent      => :destroy    # or :delete
 
-      :class_name     => "Person"
-      :select         => "*"
-      :counter_cache  => true
-      :counter_cache  => :custom_counter
-      :include        => "Book"
-      :readonly       => true
+  :class_name     => "Person"
+  :select         => "*"
+  :counter_cache  => true
+  :counter_cache  => :custom_counter
+  :include        => "Book"
+  :readonly       => true
 
-      :conditions     => 'published = true'
+  :conditions     => 'published = true'
 
-      :touch          => true
-      :touch          => :authors_last_updated_at
+  :touch          => true
+  :touch          => :authors_last_updated_at
 
-      :primary_key    => "name"
-      :foreign_key    => "author_name"
+  :primary_key    => "name"
+  :foreign_key    => "author_name"
+```
 
 ### Many-to-many
 
 If you have a join model:
+{: .-setup}
 
-    class Programmer < ActiveRecord::Base
-      has_many :assignments
-      has_many :projects, :through => :assignments
-    end
+```ruby
+class Programmer < ActiveRecord::Base
+  has_many :assignments
+  has_many :projects, :through => :assignments
+end
+```
+{: data-line="2,3"}
 
-    class Project < ActiveRecord::Base
-      has_many :assignments
-      has_many :programmers, :through => :assignments
-    end
+```ruby
+class Project < ActiveRecord::Base
+  has_many :assignments
+  has_many :programmers, :through => :assignments
+end
+```
+{: data-line="2,3"}
 
-    class Assignment
-      belongs_to :project
-      belongs_to :programmer
-    end
+```ruby
+class Assignment
+  belongs_to :project
+  belongs_to :programmer
+end
+```
+{: data-line="2,3"}
 
-Or HABTM:
+### Many-to-many (HABTM)
 
-    has_and_belongs_to_many :projects
-    has_and_belongs_to_many :projects, :include => [ :milestones, :manager ]
-    has_and_belongs_to_many :nations, :class_name => "Country"
-    has_and_belongs_to_many :categories, :join_table => "prods_cats"
-    has_and_belongs_to_many :categories, :readonly => true
-    has_and_belongs_to_many :active_projects, :join_table => 'developers_projects', :delete_sql =>
-    "DELETE FROM developers_projects WHERE active=1 AND developer_id = #{id} AND project_id = #{record.id}"
+```ruby
+has_and_belongs_to_many :projects
+has_and_belongs_to_many :projects, :include => [ :milestones, :manager ]
+has_and_belongs_to_many :nations, :class_name => "Country"
+has_and_belongs_to_many :categories, :join_table => "prods_cats"
+has_and_belongs_to_many :categories, :readonly => true
+has_and_belongs_to_many :active_projects, :join_table => 'developers_projects', :delete_sql =>
+"DELETE FROM developers_projects WHERE active=1 AND developer_id = #{id} AND project_id = #{record.id}"
+```
 
 ### Polymorphic associations
 
-    class Post
-      has_many :attachments, :as => :parent
-    end
+```ruby
+class Post
+  has_many :attachments, as: :parent
+end
+```
+{: data-line="2"}
 
-    class Image
-      belongs_to :parent, :polymorphic => true
-    end
+```ruby
+class Image
+  belongs_to :parent, polymorphic: true
+end
+```
+{: data-line="2"}
 
 And in migrations:
 
-    create_table :images do |t|
-      t.references :post, :polymorphic => true
-    end
-
-### Dynamic attribute-based finders
-
-    # Returns one record
-    Person.find_by_name(name)
-    Person.find_last_by_name(name)
-    Person.find_or_create_by_name(name)
-    Person.find_or_initialize_by_name(name)
-
-    # Returns a list of recordns
-    Person.find_all_by_name(name)
-
-    # Add a bang to make it raise an exception
-    Person.find_by_name!(name)
-
-    # You may use `scoped` instead of `find`
-    Person.scoped_by_user_name
+```ruby
+create_table :images do |t|
+  t.references :post, polymorphic: true
+end
+```
+{: data-line="2"}
 
 Validation
 ----------
 
-    class Person < ActiveRecord::Base
+### Validation
 
-      validates :name,     presence: true
+```ruby
+class Person < ActiveRecord::Base
+```
+{:.-setup}
 
-      validates :terms,    acceptance: true
+```ruby
+  # Presence
+  validates :name,     presence: true
+```
+{: data-line="2"}
 
-      validates :email,    confirmation: true
+```ruby
+  # Acceptance
+  validates :terms,    acceptance: true
+```
 
-      validates :slug,     uniqueness: true
-      validates :slug,     uniqueness: { case_sensitive: false }
-      validates :holiday,  uniqueness: { scope: :year, :message => "only once a year" }
+```ruby
+  # Confirm
+  validates :email,    confirmation: true
+```
 
-      validates :code,     format: /regex/
-      validates :code,     format: { with: /regex/ }
+```ruby
+  # Unique
+  validates :slug,     uniqueness: true
+  validates :slug,     uniqueness: { case_sensitive: false }
+  validates :holiday,  uniqueness: { scope: :year, message: 'yearly only' }
+```
 
-      validates :name,     length: { minimum: 2 }
-      validates :bio,      length: { maximum: 500 }
-      validates :password, length: { in: => 6..20 }
-      validates :number,   length: { is: => 6 }
+```ruby
+  # Format
+  validates :code,     format: /regex/
+  validates :code,     format: { with: /regex/ }
+```
 
-      validates :gender,   inclusion: %w(male female)
-      validates :gender,   inclusion: { in: %w(male female) }
-      validates :lol,      exclusion: %w(xyz)
+```ruby
+  # Length
+  validates :name,     length: { minimum: 2 }
+  validates :bio,      length: { maximum: 500 }
+  validates :password, length: { in: => 6..20 }
+  validates :number,   length: { is: => 6 }
+```
 
-      validates :points,   numericality: true
-      validates :played,   numericality: { only_integer: true }
-      # ... greater_than, greater_than_or_equal_to,
-      # ... less_than, less_than_or_equal_to
-      # ... odd, even, equal_to
+```ruby
+  # Include/exclude
+  validates :gender,   inclusion: %w(male female)
+  validates :gender,   inclusion: { in: %w(male female) }
+  validates :lol,      exclusion: %w(xyz)
+```
 
-      # Validate the associated records to ensure they're valid as well
-      has_many :books
-      validates_associated :books
+```ruby
+  # Numeric
+  validates :points,   numericality: true
+  validates :played,   numericality: { only_integer: true }
+  # ... greater_than, greater_than_or_equal_to,
+  # ... less_than, less_than_or_equal_to
+  # ... odd, even, equal_to
+```
 
-      # Length (full enchalada)
-      validates :content, length: {
-        minimum:   300,
-        maximum:   400,
-        tokenizer: lambda { |str| str.scan(/\w+/) },
-        too_short: "must have at least %{count} words",
-        too_long:  "must have at most %{count} words" }
+```ruby
+  # Validate the associated records to ensure they're valid as well
+  has_many :books
+  validates_associated :books
+```
 
-      # Multiple
-      validates :login, :email, presence: true
+```ruby
+  # Length (full options)
+  validates :content, length: {
+    minimum:   300,
+    maximum:   400,
+    tokenizer: lambda { |str| str.scan(/\w+/) },
+    too_short: "must have at least %{count} words",
+    too_long:  "must have at most %{count} words" }
+```
 
-      # Conditional
-      validates :description, presence: true, if: :published?
-      validates :description, presence: true, if: lambda { |obj| .. }
+```ruby
+  # Multiple
+  validates :login, :email, presence: true
+```
 
-      validates :title, presence: true, on: :save   # :save | :create | :update
-    end
+```ruby
+  # Conditional
+  validates :description, presence: true, if: :published?
+  validates :description, presence: true, if: lambda { |obj| .. }
+```
+
+```ruby
+  validates :title, presence: true, on: :save   # :save | :create | :update
+```
+
+```ruby
+end
+```
+{: .-setup}
 
 ### Custom validations
 
-    class Person < ActiveRecord::Base
-      validate :foo_cant_be_nil
+```ruby
+class Person < ActiveRecord::Base
+  validate :foo_cant_be_nil
 
-      def foo_cant_be_nil
-        errors.add(:foo, 'cant be nil')  if foo.nil?
-      end
-    end
+  def foo_cant_be_nil
+    errors.add(:foo, 'cant be nil')  if foo.nil?
+  end
+end
+```
+{: data-line="2"}
 
 ### Errors
 
-    record.errors.valid?      #=> false
-    record.errors             #=> { :name => ["can't be blank"] }
-    record.errors.messages    #=> { :name => ["can't be blank"] }
+```ruby
+record.errors.valid?      # → false
+record.errors             # → { :name => ["can't be blank"] }
+record.errors.messages    # → { :name => ["can't be blank"] }
+```
 
-    record.errors[:name].any?
+```ruby
+record.errors[:name].any?
+```
 
 Other API
 ---------
@@ -342,70 +485,109 @@ Other API
 
 ### Mass updates
 
-    # Updates person id 15
-    Person.update 15, name: "John", age: 24
-    Person.update [1,2], [{name: "John"}, {name: "foo"}]
+ ```ruby
+# Updates person id 15
+Person.update 15, name: "John", age: 24
+Person.update [1,2], [{name: "John"}, {name: "foo"}]
+```
 
 ### Joining
 
-    Student.joins(:schools).where(schools: { type: 'public' })
-    Student.joins(:schools).where('schools.type' => 'public' )
+```ruby
+# Basic joins
+Student.joins(:schools).where(schools: { type: 'public' })
+Student.joins(:schools).where('schools.type' => 'public' )
+```
 
-    # multiple associations
-    Article.joins(:category, :comments)
+```ruby
+# Multiple associations
+Article.joins(:category, :comments)
+```
 
-    # nested assocations
-    Article.joins(comments: :guest)
+```ruby
+# Nested assocations
+Article.joins(comments: :guest)
+```
 
-    # sql
-    Author.joins("INNER JOIN posts ON posts.author_id = authors.id AND posts.published = 't'")
+```ruby
+# SQL
+Author.joins(
+  'INNER JOIN posts ' +
+  'ON posts.author_id = authors.id ' +
+  'AND posts.published = "t"'
+)
+```
 
 ### Where interpolation
 
-    where("name = ?", "John")
-    where(["name = :name", { name: "John" }])
+```ruby
+where('name = ?', 'John')
+where(['name = :name', { name: 'John' }])
+```
 
 ### Serialize
 
-    class User < ActiveRecord::Base
-      serialize :preferences
-    end
+```ruby
+class User < ActiveRecord::Base
+  serialize :preferences
+end
+```
+{: data-line="2"}
 
-    user = User.create(:preferences => { "background" => "black", "display" => large })
+```ruby
+user = User.create(
+  preferences: {
+    'background' => 'black',
+    'display' => 'large'
+  }
+)
+```
 
 You can also specify a class option as the second parameter that’ll raise an 
 exception if a serialized object is retrieved as a descendant of a class not in 
 the hierarchy.
 
-    class User < ActiveRecord::Base
-      serialize :preferences, Hash
-    end
+```ruby
+# Only Hash allowed!
+class User < ActiveRecord::Base
+  serialize :preferences, Hash
+end
+```
+{: data-line="3"}
 
-    user = User.create(:preferences => %w( one two three ))
-    User.find(user.id).preferences    # raises SerializationTypeMismatch
+```ruby
+# Reading it raises SerializationTypeMismatch
+user = User.create(preferences: %w(one two three))
+User.find(user.id).preferences
+```
 
-Overriding accessors
---------------------
+Other tricks
+------------
 
-    class Song < ActiveRecord::Base
-      # Uses an integer of seconds to hold the length of the song
+### Overriding accessors
 
-      def length=(minutes)
-        write_attribute(:length, minutes.to_i * 60)
-      end
+```ruby
+class Song < ActiveRecord::Base
+  # Uses an integer of seconds to hold the length of the song
 
-      def length
-        read_attribute(:length) / 60
-      end
-    end
+  def length=(minutes)
+    write_attribute(:length, minutes.to_i * 60)
+  end
 
- * http://api.rubyonrails.org/classes/ActiveRecord/Base.html
+  def length
+    read_attribute(:length) / 60
+  end
+end
+```
+{: data-line="4,8"}
+
+See: <http://api.rubyonrails.org/classes/ActiveRecord/Base.html>
 
 Callbacks
 ---------
 
-    after_create
-    after_initialize
-    after_validation
-    after_save
-    after_commit
+- after_create
+- after_initialize
+- after_validation
+- after_save
+- after_commit