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-rw-r--r--guides/CHANGELOG.md4
-rw-r--r--guides/source/4_2_release_notes.md27
-rw-r--r--guides/source/action_controller_overview.md63
-rw-r--r--guides/source/active_job_basics.md2
-rw-r--r--guides/source/active_record_basics.md2
-rw-r--r--guides/source/active_record_migrations.md6
-rw-r--r--guides/source/active_record_querying.md37
-rw-r--r--guides/source/asset_pipeline.md4
-rw-r--r--guides/source/association_basics.md46
-rw-r--r--guides/source/constant_autoloading_and_reloading.md1218
-rw-r--r--guides/source/documents.yaml4
-rw-r--r--guides/source/getting_started.md54
-rw-r--r--guides/source/layouts_and_rendering.md5
-rw-r--r--guides/source/security.md8
-rw-r--r--guides/source/upgrading_ruby_on_rails.md39
15 files changed, 1386 insertions, 133 deletions
diff --git a/guides/CHANGELOG.md b/guides/CHANGELOG.md
index afaa404ac1..5a65f1355e 100644
--- a/guides/CHANGELOG.md
+++ b/guides/CHANGELOG.md
@@ -1 +1,5 @@
+* New section in Active Record Querying: Understanding The Method Chaining
+
+ *andreynering*
+
Please check [4-2-stable](https://github.com/rails/rails/blob/4-2-stable/guides/CHANGELOG.md) for previous changes.
diff --git a/guides/source/4_2_release_notes.md b/guides/source/4_2_release_notes.md
index 1e9107a8c6..d8700539c4 100644
--- a/guides/source/4_2_release_notes.md
+++ b/guides/source/4_2_release_notes.md
@@ -509,6 +509,17 @@ Please refer to the [Changelog][action-pack] for detailed changes.
serving assets from your Rails server in production.
([Pull Request](https://github.com/rails/rails/pull/16466))
+* When calling the `process` helpers in an integration test the path needs to have
+ a leading slash. Previously you could omit it but that was a byproduct of the
+ implementation and not an intentional feature, e.g.:
+
+ ```ruby
+ test "list all posts" do
+ get "/posts"
+ assert_response :success
+ end
+ ```
+
Action View
-----------
@@ -544,17 +555,6 @@ Please refer to the [Changelog][action-view] for detailed changes.
* Placeholder I18n follows the same convention as `label` I18n.
([Pull Request](https://github.com/rails/rails/pull/16438))
-* When calling the `process` helpers in an integration test the path needs to have
- a leading slash. Previously you could omit it but that was a byproduct of the
- implementation and not an intentional feature, e.g.:
-
- ```ruby
-   test "list all posts" do
-     get "/posts"
-     assert_response :success 
- end
- ```
-
Action Mailer
-------------
@@ -640,6 +640,10 @@ Please refer to the [Changelog][active-record] for detailed changes.
`Relation` for performing queries and updates is the preferred API.
([Commit](https://github.com/rails/rails/commit/d5902c9e))
+* Deprecated `add_timestamps` and `t.timestamps` without passing the `:null`
+ option. The default of `null: true` will change in Rails 5 to `null: false`.
+ ([Pull Request](https://github.com/rails/rails/pull/16481))
+
* Deprecated `Reflection#source_macro` without replacement as it is no longer
needed in Active Record.
([Pull Request](https://github.com/rails/rails/pull/16373))
@@ -824,6 +828,7 @@ Please refer to the [Changelog][active-support] for detailed changes.
`module Foo; extend ActiveSupport::Concern; end` boilerplate.
([Commit](https://github.com/rails/rails/commit/b16c36e688970df2f96f793a759365b248b582ad))
+* New [guide](constant_autoloading_and_reloading.html) about constant autoloading and reloading.
Credits
-------
diff --git a/guides/source/action_controller_overview.md b/guides/source/action_controller_overview.md
index 1ca0d9ed55..57546da389 100644
--- a/guides/source/action_controller_overview.md
+++ b/guides/source/action_controller_overview.md
@@ -112,8 +112,8 @@ NOTE: The actual URL in this example will be encoded as "/clients?ids%5b%5d=1&id
The value of `params[:ids]` will now be `["1", "2", "3"]`. Note that parameter values are always strings; Rails makes no attempt to guess or cast the type.
-NOTE: Values such as `[]`, `[nil]` or `[nil, nil, ...]` in `params` are replaced
-with `nil` for security reasons by default. See [Security Guide](security.html#unsafe-query-generation)
+NOTE: Values such as `[nil]` or `[nil, nil, ...]` in `params` are replaced
+with `[]` for security reasons by default. See [Security Guide](security.html#unsafe-query-generation)
for more information.
To send a hash you include the key name inside the brackets:
@@ -1164,67 +1164,10 @@ class ClientsController < ApplicationController
end
```
-WARNING: You shouldn't do `rescue_from Exception` or `rescue_from StandardError` unless you have a particular reason as it will cause serious side-effects (e.g. you won't be able to see exception details and tracebacks during development). If you would like to dynamically generate error pages, see [Custom errors page](#custom-errors-page).
+WARNING: You shouldn't do `rescue_from Exception` or `rescue_from StandardError` unless you have a particular reason as it will cause serious side-effects (e.g. you won't be able to see exception details and tracebacks during development).
NOTE: Certain exceptions are only rescuable from the `ApplicationController` class, as they are raised before the controller gets initialized and the action gets executed. See Pratik Naik's [article](http://m.onkey.org/2008/7/20/rescue-from-dispatching) on the subject for more information.
-
-### Custom errors page
-
-You can customize the layout of your error handling using controllers and views.
-First define your app own routes to display the errors page.
-
-* `config/application.rb`
-
- ```ruby
- config.exceptions_app = self.routes
- ```
-
-* `config/routes.rb`
-
- ```ruby
- match '/404', via: :all, to: 'errors#not_found'
- match '/422', via: :all, to: 'errors#unprocessable_entity'
- match '/500', via: :all, to: 'errors#server_error'
- ```
-
-Create the controller and views.
-
-* `app/controllers/errors_controller.rb`
-
- ```ruby
- class ErrorsController < ActionController::Base
- layout 'error'
-
- def not_found
- render status: :not_found
- end
-
- def unprocessable_entity
- render status: :unprocessable_entity
- end
-
- def server_error
- render status: :server_error
- end
- end
- ```
-
-* `app/views`
-
- ```
- errors/
- not_found.html.erb
- unprocessable_entity.html.erb
- server_error.html.erb
- layouts/
- error.html.erb
- ```
-
-Do not forget to set the correct status code on the controller as shown before.
-
-WARNING: You should avoid using the database or any complex operations because the user is already on the error page. Generating another error while on an error page could cause issues like presenting an empty page for the users.
-
Force HTTPS protocol
--------------------
diff --git a/guides/source/active_job_basics.md b/guides/source/active_job_basics.md
index 748467866d..3657d7cad7 100644
--- a/guides/source/active_job_basics.md
+++ b/guides/source/active_job_basics.md
@@ -155,7 +155,7 @@ end
# environment
```
-The default queue name prefix delimiter is '_'. This can be changed by setting
+The default queue name prefix delimiter is '\_'. This can be changed by setting
`config.active_job.queue_name_delimiter` in `application.rb`:
```ruby
diff --git a/guides/source/active_record_basics.md b/guides/source/active_record_basics.md
index bd074d0055..ef86531eef 100644
--- a/guides/source/active_record_basics.md
+++ b/guides/source/active_record_basics.md
@@ -358,7 +358,7 @@ class CreatePublications < ActiveRecord::Migration
t.string :publisher_type
t.boolean :single_issue
- t.timestamps
+ t.timestamps null: false
end
add_index :publications, :publication_type_id
end
diff --git a/guides/source/active_record_migrations.md b/guides/source/active_record_migrations.md
index 1a41fc8b4c..e76a57e164 100644
--- a/guides/source/active_record_migrations.md
+++ b/guides/source/active_record_migrations.md
@@ -39,7 +39,7 @@ class CreateProducts < ActiveRecord::Migration
t.string :name
t.text :description
- t.timestamps
+ t.timestamps null: false
end
end
end
@@ -285,7 +285,7 @@ class CreateProducts < ActiveRecord::Migration
t.string :name
t.text :description
- t.timestamps
+ t.timestamps null: false
end
end
end
@@ -826,7 +826,7 @@ class CreateProducts < ActiveRecord::Migration
create_table :products do |t|
t.string :name
t.text :description
- t.timestamps
+ t.timestamps null: false
end
end
diff --git a/guides/source/active_record_querying.md b/guides/source/active_record_querying.md
index e1a465c64f..f6fbc29707 100644
--- a/guides/source/active_record_querying.md
+++ b/guides/source/active_record_querying.md
@@ -9,6 +9,7 @@ After reading this guide, you will know:
* How to specify the order, retrieved attributes, grouping, and other properties of the found records.
* How to use eager loading to reduce the number of database queries needed for data retrieval.
* How to use dynamic finders methods.
+* How to use method chaining to use multiple ActiveRecord methods together.
* How to check for the existence of particular records.
* How to perform various calculations on Active Record models.
* How to run EXPLAIN on relations.
@@ -1327,10 +1328,44 @@ You can specify an exclamation point (`!`) on the end of the dynamic finders to
If you want to find both by name and locked, you can chain these finders together by simply typing "`and`" between the fields. For example, `Client.find_by_first_name_and_locked("Ryan", true)`.
+Understanding The Method Chaining
+---------------------------------
+
+The ActiveRecord pattern implements [Method Chaining](http://en.wikipedia.org/wiki/Method_chaining).
+This allow us to use multiple ActiveRecord methods in a simple and straightforward way.
+
+You can chain a method in a sentence when the previous method called returns `ActiveRecord::Relation`,
+like `all`, `where`, and `joins`. Methods that returns a instance of a single object
+(see [Retrieving a Single Object Section](#retrieving-a-single-object)) have to be be the last
+in the sentence.
+
+This guide won't cover all the possibilities, just a few as example.
+
+### Retrieving filtered data from multiple tables
+
+```ruby
+Person
+ .select('people.id, people.name, comments.text')
+ .joins(:comments)
+ .where('comments.create_at > ?', 1.week.ago)
+```
+
+### Retrieving specific data from multiple tables
+
+```ruby
+Person
+ .select('people.id, people.name, companies.name')
+ .joins(:company)
+ .find_by('people.name' => 'John') # this should be the last
+```
+
+NOTE: Remember that, if `find_by` return more than one registry, it will take just the first
+and ignore the others.
+
Find or Build a New Object
--------------------------
-NOTE: Some dynamic finders have been deprecated in Rails 4.0 and will be
+NOTE: Some dynamic finders were deprecated in Rails 4.0 and
removed in Rails 4.1. The best practice is to use Active Record scopes
instead. You can find the deprecation gem at
https://github.com/rails/activerecord-deprecated_finders
diff --git a/guides/source/asset_pipeline.md b/guides/source/asset_pipeline.md
index ae0f19c02a..8764546873 100644
--- a/guides/source/asset_pipeline.md
+++ b/guides/source/asset_pipeline.md
@@ -231,7 +231,9 @@ images, JavaScript files or stylesheets.
scope of the application or those libraries which are shared across applications.
* `vendor/assets` is for assets that are owned by outside entities, such as
-code for JavaScript plugins and CSS frameworks.
+code for JavaScript plugins and CSS frameworks. Keep in mind that third party
+code with references to other files also processed by the asset Pipeline (images,
+stylesheets, etc.), will need to be rewritten to use helpers like `asset_path`.
WARNING: If you are upgrading from Rails 3, please take into account that assets
under `lib/assets` or `vendor/assets` are available for inclusion via the
diff --git a/guides/source/association_basics.md b/guides/source/association_basics.md
index a12f5638e3..5c05f0c4b7 100644
--- a/guides/source/association_basics.md
+++ b/guides/source/association_basics.md
@@ -101,13 +101,13 @@ class CreateOrders < ActiveRecord::Migration
def change
create_table :customers do |t|
t.string :name
- t.timestamps
+ t.timestamps null: false
end
create_table :orders do |t|
t.belongs_to :customer, index: true
t.datetime :order_date
- t.timestamps
+ t.timestamps null: false
end
end
end
@@ -132,13 +132,13 @@ class CreateSuppliers < ActiveRecord::Migration
def change
create_table :suppliers do |t|
t.string :name
- t.timestamps
+ t.timestamps null: false
end
create_table :accounts do |t|
t.belongs_to :supplier, index: true
t.string :account_number
- t.timestamps
+ t.timestamps null: false
end
end
end
@@ -165,13 +165,13 @@ class CreateCustomers < ActiveRecord::Migration
def change
create_table :customers do |t|
t.string :name
- t.timestamps
+ t.timestamps null: false
end
create_table :orders do |t|
t.belongs_to :customer, index:true
t.datetime :order_date
- t.timestamps
+ t.timestamps null: false
end
end
end
@@ -207,19 +207,19 @@ class CreateAppointments < ActiveRecord::Migration
def change
create_table :physicians do |t|
t.string :name
- t.timestamps
+ t.timestamps null: false
end
create_table :patients do |t|
t.string :name
- t.timestamps
+ t.timestamps null: false
end
create_table :appointments do |t|
t.belongs_to :physician, index: true
t.belongs_to :patient, index: true
t.datetime :appointment_date
- t.timestamps
+ t.timestamps null: false
end
end
end
@@ -291,19 +291,19 @@ class CreateAccountHistories < ActiveRecord::Migration
def change
create_table :suppliers do |t|
t.string :name
- t.timestamps
+ t.timestamps null: false
end
create_table :accounts do |t|
t.belongs_to :supplier, index: true
t.string :account_number
- t.timestamps
+ t.timestamps null: false
end
create_table :account_histories do |t|
t.belongs_to :account, index: true
t.integer :credit_rating
- t.timestamps
+ t.timestamps null: false
end
end
end
@@ -332,12 +332,12 @@ class CreateAssembliesAndParts < ActiveRecord::Migration
def change
create_table :assemblies do |t|
t.string :name
- t.timestamps
+ t.timestamps null: false
end
create_table :parts do |t|
t.string :part_number
- t.timestamps
+ t.timestamps null: false
end
create_table :assemblies_parts, id: false do |t|
@@ -371,13 +371,13 @@ class CreateSuppliers < ActiveRecord::Migration
def change
create_table :suppliers do |t|
t.string :name
- t.timestamps
+ t.timestamps null: false
end
create_table :accounts do |t|
t.integer :supplier_id
t.string :account_number
- t.timestamps
+ t.timestamps null: false
end
add_index :accounts, :supplier_id
@@ -455,7 +455,7 @@ class CreatePictures < ActiveRecord::Migration
t.string :name
t.integer :imageable_id
t.string :imageable_type
- t.timestamps
+ t.timestamps null: false
end
add_index :pictures, :imageable_id
@@ -471,7 +471,7 @@ class CreatePictures < ActiveRecord::Migration
create_table :pictures do |t|
t.string :name
t.references :imageable, polymorphic: true, index: true
- t.timestamps
+ t.timestamps null: false
end
end
end
@@ -501,7 +501,7 @@ class CreateEmployees < ActiveRecord::Migration
def change
create_table :employees do |t|
t.references :manager, index: true
- t.timestamps
+ t.timestamps null: false
end
end
end
@@ -879,10 +879,12 @@ class Order < ActiveRecord::Base
belongs_to :customer, counter_cache: :count_of_orders
end
class Customer < ActiveRecord::Base
- has_many :orders
+ has_many :orders, counter_cache: :count_of_orders
end
```
+NOTE: You only need to specify the :counter_cache option on the "has_many side" of the association when using a custom name for the counter cache.
+
Counter cache columns are added to the containing model's list of read-only attributes through `attr_readonly`.
##### `:dependent`
@@ -1495,6 +1497,7 @@ The `has_many` association supports these options:
* `:as`
* `:autosave`
* `:class_name`
+* `:counter_cache`
* `:dependent`
* `:foreign_key`
* `:inverse_of`
@@ -1522,6 +1525,9 @@ class Customer < ActiveRecord::Base
end
```
+##### `:counter_cache`
+This option can be used to configure a custom named `:counter_cache`. You only need this option when you customized the name of your `:counter_cache` on the [belongs_to association](#options-for-belongs-to).
+
##### `:dependent`
Controls what happens to the associated objects when their owner is destroyed:
diff --git a/guides/source/constant_autoloading_and_reloading.md b/guides/source/constant_autoloading_and_reloading.md
new file mode 100644
index 0000000000..ab8ef399e7
--- /dev/null
+++ b/guides/source/constant_autoloading_and_reloading.md
@@ -0,0 +1,1218 @@
+Constant Autoloading and Reloading
+==================================
+
+This guide documents how constant autoloading and reloading works.
+
+After reading this guide, you will know:
+
+* Key aspects of Ruby constants
+* What is `autoload_paths`
+* How constant autoloading works
+* What is `require_dependency`
+* How constant reloading works
+* Solutions to common autoloading gotchas
+
+--------------------------------------------------------------------------------
+
+
+Introduction
+------------
+
+Ruby on Rails allows applications to be written as if their code was preloaded.
+
+In a normal Ruby program a class needs to load its dependencies:
+
+```ruby
+require 'application_controller'
+require 'post'
+
+class PostsController < ApplicationController
+ def index
+ @posts = Post.all
+ end
+end
+```
+
+Our Rubyist instinct quickly sees some redundancy in there: If classes were
+defined in files matching their name, couldn't their loading be automated
+somehow? We could save scanning the file for dependencies, which is brittle.
+
+Moreover, `Kernel#require` loads files once, but development is much more smooth
+if code gets refreshed when it changes without restarting the server. It would
+be nice to be able to use `Kernel#load` in development, and `Kernel#require` in
+production.
+
+Indeed, those features are provided by Ruby on Rails, where we just write
+
+```ruby
+class PostsController < ApplicationController
+ def index
+ @posts = Post.all
+ end
+end
+```
+
+This guide documents how that works.
+
+
+Constants Refresher
+-------------------
+
+While constants are trivial in most programming languages, they are a rich
+topic in Ruby.
+
+It is beyond the scope of this guide to document Ruby constants, but we are
+nevertheless going to highlight a few key topics. Truly grasping the following
+sections is instrumental to understanding constant autoloading and reloading.
+
+### Nesting
+
+Class and module definitions can be nested to create namespaces:
+
+```ruby
+module XML
+ class SAXParser
+ # (1)
+ end
+end
+```
+
+The *nesting* at any given place is the collection of enclosing nested class and
+module objects outwards. For example, in the previous example, the nesting at
+(1) is
+
+```ruby
+[XML::SAXParser, XML]
+```
+
+It is important to understand that the nesting is composed of class and module
+*objects*, it has nothing to do with the constants used to access them, and is
+also unrelated to their names.
+
+For instance, while this definition is similar to the previous one:
+
+```ruby
+class XML::SAXParser
+ # (2)
+end
+```
+
+the nesting in (2) is different, `XML` does not belong to it:
+
+```ruby
+[XML::SAXParser]
+```
+
+We can see in this example that the name of a class or module that belongs to a
+certain nesting does not necessarily correlate with the namespaces at the spot.
+
+Even more, they are totally independent, take for instance
+
+```ruby
+module X::Y
+ module A::B
+ # (3)
+ end
+end
+```
+
+The nesting in (3) consists of two module objects:
+
+```ruby
+[A::B, X::Y]
+```
+
+So, it not only doesn't end in `A`, which does not even belong to the nesting,
+but it also contains `X::Y`, which is independent from `A::B`.
+
+The nesting is an internal stack maintained by the interpreter, and it gets
+modified according to these rules:
+
+* The class object following a `class` keyword gets pushed when its body is
+executed, and popped after it.
+
+* The module object following a `module` keyword gets pushed when its body is
+executed, and popped after it.
+
+* A singleton class opened with `class << object` gets pushed, and popped later.
+
+* When any of the `*_eval` family of methods is called using a string argument,
+the singleton class of the receiver is pushed to the nesting of the eval'ed
+code.
+
+* The nesting at the top-level of code interpreted by `Kernel#load` is empty
+unless the `load` call receives a true value as second argument, in which case
+a newly created anonymous module is pushed by Ruby.
+
+It is interesting to observe that blocks do not modify the stack. In particular
+the blocks that may be passed to `Class.new` and `Module.new` do not get the
+class or module being defined pushed to their nesting. That's one of the
+differences between defining classes and modules in one way or another.
+
+The nesting at any given place can be inspected with `Module.nesting`.
+
+### Class and Module Definitions are Constant Assignments
+
+Let's suppose the following snippet creates a class (rather than reopening it):
+
+```ruby
+class C
+end
+```
+
+Ruby creates a constant `C` in `Object` and stores in that constant a class
+object. The name of the class instance is "C", a string, named after the
+constant.
+
+That is,
+
+```ruby
+class Project < ActiveRecord::Base
+end
+```
+
+performs a constant assignment equivalent to
+
+```ruby
+Project = Class.new(ActiveRecord::Base)
+```
+
+Similarly, module creation using the `module` keyword as in
+
+```ruby
+module Admin
+end
+```
+
+performs a constant assignment equivalent to
+
+```ruby
+Admin = Module.new
+```
+
+WARNING. The execution context of a block passed to `Class.new` or `Module.new`
+is not entirely equivalent to the one of the body of the definitions using the
+`class` and `module` keywords. But both idioms result in the same constant
+assignment.
+
+Thus, when one informally says "the `String` class", that really means: the
+class object the interpreter creates and stores in a constant called "String" in
+the class object stored in the `Object` constant. `String` is otherwise an
+ordinary Ruby constant and everything related to constants applies to it,
+resolution algorithms, etc.
+
+Likewise, in the controller
+
+```ruby
+class PostsController < ApplicationController
+ def index
+ @posts = Post.all
+ end
+end
+```
+
+`Post` is not syntax for a class. Rather, `Post` is a regular Ruby constant. If
+all is good, the constant evaluates to an object that responds to `all`.
+
+That is why we talk about *constant autoloading*, Rails has the ability to load
+constants on the fly.
+
+### Constants are Stored in Modules
+
+Constants belong to modules in a very literal sense. Classes and modules have
+a constant table; think of it as a hash table.
+
+Let's analyze an example to really understand what that means. While in a
+casual setting some abuses of language are customary, the exposition is going
+to be exact here for didactic purposes.
+
+Let's consider the following module definition:
+
+```ruby
+module Colors
+ RED = '0xff0000'
+end
+```
+
+First, when the `module` keyword is processed the interpreter creates a new
+entry in the constant table of the class object stored in the `Object` constant.
+Said entry associates the name "Colors" to a newly created module object.
+Furthermore, the interpreter sets the name of the new module object to be the
+string "Colors".
+
+Later, when the body of the module definition is interpreted, a new entry is
+created in the constant table of the module object stored in the `Colors`
+constant. That entry maps the name "RED" to the string "0xff0000".
+
+In particular, `Colors::RED` is totally unrelated to any other `RED` constant
+that may live in any other class or module object. If there were any, they
+would have separate entries in their respective constant tables.
+
+Put special attention in the previous paragraphs to the distinction between
+class and module objects, constant names, and value objects associated to them
+in constant tables.
+
+### Resolution Algorithms
+
+#### Resolution Algorithm for Relative Constants
+
+At any given place in the code, let's define *cref* to be the first element of
+the nesting if it is not empty, or `Object` otherwise.
+
+Without getting too much into the details, the resolution algorithm for relative
+constant references goes like this:
+
+1. If the nesting is not empty the constant is looked up in its elements and in
+order. The ancestors of those elements are ignored.
+
+2. If not found, then the algorithm walks up the ancestor chain of the cref.
+
+3. If not found, `const_missing` is invoked on the cref. The default
+implementation of `const_missing` raises `NameError`, but it can be overridden.
+
+Rails autoloading **does not emulate this algorithm**, but its starting point is
+the name of the constant to be autoloaded, and the cref. See more in [Relative
+References](#relative-references).
+
+#### Resolution Algorithm for Qualified Constants
+
+Qualified constants look like this:
+
+```ruby
+Billing::Invoice
+```
+
+`Billing::Invoice` is composed of two constants: `Billing` is relative and is
+resolved using the algorithm of the previous section; `Invoice` is qualified by
+`Billing` and we are going to see its resolution next. Let's call *parent* to
+that qualifying class or module object, that is, `Billing` in the example above.
+The algorithm for qualified constants goes like this:
+
+1. The constant is looked up in the parent and its ancestors.
+
+2. If the lookup fails, `const_missing` is invoked in the parent. The default
+implementation of `const_missing` raises `NameError`, but it can be overridden.
+
+As you see, this algorithm is simpler than the one for relative constants. In
+particular, the nesting plays no role here, and modules are not special-cased,
+if neither they nor their ancestors have the constants, `Object` is **not**
+checked.
+
+Rails autoloading **does not emulate this algorithm**, but its starting point is
+the name of the constant to be autoloaded, and the parent. See more in
+[Qualified References](#qualified-references).
+
+
+Vocabulary
+----------
+
+### Parent Namespaces
+
+Given a string with a constant path we define its *parent namespace* to be the
+string that results from removing its rightmost segment.
+
+For example, the parent namespace of the string "A::B::C" is the string "A::B",
+the parent namespace of "A::B" is "A", and the parent namespace of "A" is "".
+
+The interpretation of a parent namespace when thinking about classes and modules
+is tricky though. Let's consider a module M named "A::B":
+
+* The parent namespace, "A", may not reflect nesting at a given spot.
+
+* The constant `A` may no longer exist, some code could have removed it from
+`Object`.
+
+* If `A` exists, the class or module that was originally in `A` may not be there
+anymore. For example, if after a constant removal there was another constant
+assignment there would generally be a different object in there.
+
+* In such case, it could even happen that the reassigned `A` held a new class or
+module called also "A"!
+
+* In the previous scenarios M would no longer be reachable through `A::B` but
+the module object itself could still be alive somewhere and its name would
+still be "A::B".
+
+The idea of a parent namespace is at the core of the autoloading algorithms
+and helps explain and understand their motivation intuitively, but as you see
+that metaphor leaks easily. Given an edge case to reason about, take always into
+account that by "parent namespace" the guide means exactly that specific string
+derivation.
+
+### Loading Mechanism
+
+Rails autoloads files with `Kernel#load` when `config.cache_classes` is false,
+the default in development mode, and with `Kernel#require` otherwise, the
+default in production mode.
+
+`Kernel#load` allows Rails to execute files more than once if [constant
+reloading](#constant-reloading) is enabled.
+
+This guide uses the word "load" freely to mean a given file is interpreted, but
+the actual mechanism can be `Kernel#load` or `Kernel#require` depending on that
+flag.
+
+
+Autoloading Availability
+------------------------
+
+Rails is always able to autoload provided its environment is in place. For
+example the `runner` command autoloads:
+
+```
+$ bin/rails runner 'p User.column_names'
+["id", "email", "created_at", "updated_at"]
+```
+
+The console autoloads, the test suite autoloads, and of course the application
+autoloads.
+
+By default, Rails eager loads the application files when it boots in production
+mode, so most of the autoloading going on in development does not happen. But
+autoloading may still be triggered during eager loading.
+
+For example, given
+
+```ruby
+class BeachHouse < House
+end
+```
+
+if `House` is still unknown when `app/models/beach_house.rb` is being eager
+loaded, Rails autoloads it.
+
+
+autoload_paths
+--------------
+
+As you probably know, when `require` gets a relative file name:
+
+```ruby
+require 'erb'
+```
+
+Ruby looks for the file in the directories listed in `$LOAD_PATH`. That is, Ruby
+iterates over all its directories and for each one of them checks whether they
+have a file called "erb.rb", or "erb.so", or "erb.o", or "erb.dll". If it finds
+any of them, the interpreter loads it and ends the search. Otherwise, it tries
+again in the next directory of the list. If the list gets exhausted, `LoadError`
+is raised.
+
+We are going to cover how constant autoloading works in more detail later, but
+the idea is that when a constant like `Post` is hit and missing, if there's a
+`post.rb` file for example in `app/models` Rails is going to find it, evaluate
+it, and have `Post` defined as a side-effect.
+
+Alright, Rails has a collection of directories similar to `$LOAD_PATH` in which
+to look up `post.rb`. That collection is called `autoload_paths` and by
+default it contains:
+
+* All subdirectories of `app` in the application and engines. For example,
+ `app/controllers`. They do not need to be the default ones, any custom
+ directories like `app/workers` belong automatically to `autoload_paths`.
+
+* Any existing second level directories called `app/*/concerns` in the
+ application and engines.
+
+* The directory `test/mailers/previews`.
+
+Also, this collection is configurable via `config.autoload_paths`. For example,
+`lib` was in the list years ago, but no longer is. An application can opt-in
+throwing this to `config/application.rb`:
+
+```ruby
+config.autoload_paths += "#{Rails.root}/lib"
+```
+
+The value of `autoload_paths` can be inspected. In a just generated application
+it is (edited):
+
+```
+$ bin/rails r 'puts ActiveSupport::Dependencies.autoload_paths'
+.../app/assets
+.../app/controllers
+.../app/helpers
+.../app/mailers
+.../app/models
+.../app/controllers/concerns
+.../app/models/concerns
+.../test/mailers/previews
+```
+
+INFO. `autoload_paths` is computed and cached during the initialization process.
+The application needs to be restarted to reflect any changes in the directory
+structure.
+
+
+Autoloading Algorithms
+----------------------
+
+### Relative References
+
+A relative constant reference may appear in several places, for example, in
+
+```ruby
+class PostsController < ApplicationController
+ def index
+ @posts = Post.all
+ end
+end
+```
+
+all three constant references are relative.
+
+#### Constants after the `class` and `module` Keywords
+
+Ruby performs a lookup for the constant that follows a `class` or `module`
+keyword because it needs to know if the class or module is going to be created
+or reopened.
+
+If the constant is not defined at that point it is not considered to be a
+missing constant, autoloading is **not** triggered.
+
+So, in the previous example, if `PostsController` is not defined when the file
+is interpreted Rails autoloading is not going to be triggered, Ruby will just
+define the controller.
+
+#### Top-Level Constants
+
+On the contrary, if `ApplicationController` is unknown, the constant is
+considered missing and an autoload is going to be attempted by Rails.
+
+In order to load `ApplicationController`, Rails iterates over `autoload_paths`.
+First checks if `app/assets/application_controller.rb` exists. If it does not,
+which is normally the case, it continues and finds
+`app/controllers/application_controller.rb`.
+
+If the file defines the constant `ApplicationController` all is fine, otherwise
+`LoadError` is raised:
+
+```
+unable to autoload constant ApplicationController, expected
+<full path to application_controller.rb> to define it (LoadError)
+```
+
+INFO. Rails does not require the value of autoloaded constants to be a class or
+module object. For example, if the file `app/models/max_clients.rb` defines
+`MAX_CLIENTS = 100` autoloading `MAX_CLIENTS` works just fine.
+
+#### Namespaces
+
+Autoloading `ApplicationController` looks directly under the directories of
+`autoload_paths` because the nesting in that spot is empty. The situation of
+`Post` is different, the nesting in that line is `[PostsController]` and support
+for namespaces comes into play.
+
+The basic idea is that given
+
+```ruby
+module Admin
+ class BaseController < ApplicationController
+ @@all_roles = Role.all
+ end
+end
+```
+
+to autoload `Role` we are going to check if it is defined in the current or
+parent namespaces, one at a time. So, conceptually we want to try to autoload
+any of
+
+```
+Admin::BaseController::Role
+Admin::Role
+Role
+```
+
+in that order. That's the idea. To do so, Rails looks in `autoload_paths`
+respectively for file names like these:
+
+```
+admin/base_controller/role.rb
+admin/role.rb
+role.rb
+```
+
+modulus some additional directory lookups we are going to cover soon.
+
+INFO. `'Constant::Name'.underscore` gives the relative path without extension of
+the file name where `Constant::Name` is expected to be defined.
+
+Let's see how Rails autoloads the `Post` constant in the `PostsController`
+above assuming the application has a `Post` model defined in
+`app/models/post.rb`.
+
+First it checks for `posts_controller/post.rb` in `autoload_paths`:
+
+```
+app/assets/posts_controller/post.rb
+app/controllers/posts_controller/post.rb
+app/helpers/posts_controller/post.rb
+...
+test/mailers/previews/posts_controller/post.rb
+```
+
+Since the lookup is exhausted without success, a similar search for a directory
+is performed, we are going to see why in the [next section](#automatic-modules):
+
+```
+app/assets/posts_controller/post
+app/controllers/posts_controller/post
+app/helpers/posts_controller/post
+...
+test/mailers/previews/posts_controller/post
+```
+
+If all those attempts fail, then Rails starts the lookup again in the parent
+namespace. In this case only the top-level remains:
+
+```
+app/assets/post.rb
+app/controllers/post.rb
+app/helpers/post.rb
+app/mailers/post.rb
+app/models/post.rb
+```
+
+A matching file is found in `app/models/post.rb`. The lookup stops there and the
+file is loaded. If the file actually defines `Post` all is fine, otherwise
+`LoadError` is raised.
+
+### Qualified References
+
+When a qualified constant is missing Rails does not look for it in the parent
+namespaces. But there is a caveat: When a constant is missing, Rails is
+unable to tell if the trigger was a relative reference or a qualified one.
+
+For example, consider
+
+```ruby
+module Admin
+ User
+end
+```
+
+and
+
+```ruby
+Admin::User
+```
+
+If `User` is missing, in either case all Rails knows is that a constant called
+"User" was missing in a module called "Admin".
+
+If there is a top-level `User` Ruby would resolve it in the former example, but
+wouldn't in the latter. In general, Rails does not emulate the Ruby constant
+resolution algorithms, but in this case it tries using the following heuristic:
+
+> If none of the parent namespaces of the class or module has the missing
+> constant then Rails assumes the reference is relative. Otherwise qualified.
+
+For example, if this code triggers autoloading
+
+```ruby
+Admin::User
+```
+
+and the `User` constant is already present in `Object`, it is not possible that
+the situation is
+
+```ruby
+module Admin
+ User
+end
+```
+
+because otherwise Ruby would have resolved `User` and no autoloading would have
+been triggered in the first place. Thus, Rails assumes a qualified reference and
+considers the file `admin/user.rb` and directory `admin/user` to be the only
+valid options.
+
+In practice, this works quite well as long as the nesting matches all parent
+namespaces respectively and the constants that make the rule apply are known at
+that time.
+
+However, autoloading happens on demand. If by chance the top-level `User` was
+not yet loaded, then Rails has no way to know whether `Admin::User` should load
+it or raise `NameError`.
+
+Naming conflicts of this kind are rare in practice, but if one occurs,
+`require_dependency` provides a solution by ensuring that the constant needed
+to trigger the heuristic is defined in the conflicting place.
+
+### Automatic Modules
+
+When a module acts as a namespace, Rails does not require the application to
+defines a file for it, a directory matching the namespace is enough.
+
+Suppose an application has a back office whose controllers are stored in
+`app/controllers/admin`. If the `Admin` module is not yet loaded when
+`Admin::UsersController` is hit, Rails needs first to autoload the constant
+`Admin`.
+
+If `autoload_paths` has a file called `admin.rb` Rails is going to load that
+one, but if there's no such file and a directory called `admin` is found, Rails
+creates an empty module and assigns it to the `Admin` constant on the fly.
+
+### Generic Procedure
+
+Relative references are reported to be missing in the cref where they were hit,
+and qualified references are reported to be missing in their parent. (See
+[Resolution Algorithm for Relative
+Constants](#resolution-algorithm-for-relative-constants) at the beginning of
+this guide for the definition of *cref*, and [Resolution Algorithm for Qualified
+Constants](#resolution-algorithm-for-qualified-constants) for the definition of
+*parent*.)
+
+The procedure to autoload constant `C` in an arbitrary situation is as follows:
+
+```
+if the class or module in which C is missing is Object
+ let ns = ''
+else
+ let M = the class or module in which C is missing
+
+ if M is anonymous
+ let ns = ''
+ else
+ let ns = M.name
+ end
+end
+
+loop do
+ # Look for a regular file.
+ for dir in autoload_paths
+ if the file "#{dir}/#{ns.underscore}/c.rb" exists
+ load/require "#{dir}/#{ns.underscore}/c.rb"
+
+ if C is now defined
+ return
+ else
+ raise LoadError
+ end
+ end
+ end
+
+ # Look for an automatic module.
+ for dir in autoload_paths
+ if the directory "#{dir}/#{ns.underscore}/c" exists
+ if ns is an empty string
+ let C = Module.new in Object and return
+ else
+ let C = Module.new in ns.constantize and return
+ end
+ end
+ end
+
+ if ns is empty
+ # We reached the top-level without finding the constant.
+ raise NameError
+ else
+ if C exists in any of the parent namespaces
+ # Qualified constants heuristic.
+ raise NameError
+ else
+ # Try again in the parent namespace.
+ let ns = the parent namespace of ns and retry
+ end
+ end
+end
+```
+
+
+require_dependency
+------------------
+
+Constant autoloading is triggered on demand and therefore code that uses a
+certain constant may have it already defined or may trigger an autoload. That
+depends on the execution path and it may vary between runs.
+
+There are times, however, in which you want to make sure a certain constant is
+known when the execution reaches some code. `require_dependency` provides a way
+to load a file using the current [loading mechanism](#loading-mechanism), and
+keeping track of constants defined in that file as if they were autoloaded to
+have them reloaded as needed.
+
+`require_dependency` is rarely needed, but see a couple of use-cases in
+[Autoloading and STI](#autoloading-and-sti) and [When Constants aren't
+Triggered](#when-constants-aren-t-missed).
+
+WARNING. Unlike autoloading, `require_dependency` does not expect the file to
+define any particular constant. Exploiting this behavior would be a bad practice
+though, file and constant paths should match.
+
+
+Constant Reloading
+------------------
+
+When `config.cache_classes` is false Rails is able to reload autoloaded
+constants.
+
+For example, in you're in a console session and edit some file behind the
+scenes, the code can be reloaded with the `reload!` command:
+
+```
+> reload!
+```
+
+When the application runs, code is reloaded when something relevant to this
+logic changes. In order to do that, Rails monitors a number of things:
+
+* `config/routes.rb`.
+
+* Locales.
+
+* Ruby files under `autoload_paths`.
+
+* `db/schema.rb` and `db/structure.sql`.
+
+If anything in there changes, there is a middleware that detects it and reloads
+the code.
+
+Autoloading keeps track of autoloaded constants. Reloading is implemented by
+removing them all from their respective classes and modules using
+`Module#remove_const`. That way, when the code goes on, those constants are
+going to be unknown again, and files reloaded on demand.
+
+INFO. This is an all-or-nothing operation, Rails does not attempt to reload only
+what changed since dependencies between classes makes that really tricky.
+Instead, everything is wiped.
+
+
+Module#autoload isn't Involved
+------------------------------
+
+`Module#autoload` provides a lazy way to load constants that is fully integrated
+with the Ruby constant lookup algorithms, dynamic constant API, etc. It is quite
+transparent.
+
+Rails internals make extensive use of it to defer as much work as possible from
+the boot process. But constant autoloading in Rails is **not** implemented with
+`Module#autoload`.
+
+One possible implementation based on `Module#autoload` would be to walk the
+application tree and issue `autoload` calls that map existing file names to
+their conventional constant name.
+
+There are a number of reasons that prevent Rails from using that implementation.
+
+For example, `Module#autoload` is only capable of loading files using `require`,
+so reloading would not be possible. Not only that, it uses an internal `require`
+which is not `Kernel#require`.
+
+Then, it provides no way to remove declarations in case a file is deleted. If a
+constant gets removed with `Module#remove_const` its `autoload` is not triggered
+again. Also, it doesn't support qualified names, so files with namespaces should
+be interpreted during the walk tree to install their own `autoload` calls, but
+those files could have constant references not yet configured.
+
+An implementation based on `Module#autoload` would be awesome but, as you see,
+at least as of today it is not possible. Constant autoloading in Rails is
+implemented with `Module#const_missing`, and that's why it has its own contract,
+documented in this guide.
+
+
+Common Gotchas
+--------------
+
+### Nesting and Qualified Constants
+
+Let's consider
+
+```ruby
+module Admin
+ class UsersController < ApplicationController
+ def index
+ @users = User.all
+ end
+ end
+end
+```
+
+and
+
+```ruby
+class Admin::UsersController < ApplicationController
+ def index
+ @users = User.all
+ end
+end
+```
+
+To resolve `User` Ruby checks `Admin` in the former case, but it does not in
+the latter because it does not belong to the nesting. (See [Nesting](#nesting)
+and [Resolution Algorithms](#resolution- algorithms).)
+
+Unfortunately Rails autoloading does not know the nesting in the spot where the
+constant was missing and so it is not able to act as Ruby would. In particular,
+`Admin::User` will get autoloaded in either case.
+
+Albeit qualified constants with `class` and `module` keywords may technically
+work with autoloading in some cases, it is preferable to use relative constants
+instead:
+
+```ruby
+module Admin
+ class UsersController < ApplicationController
+ def index
+ @users = User.all
+ end
+ end
+end
+```
+
+### Autoloading and STI
+
+Single Table Inheritance (STI) is a feature of Active Record that easies
+storing a hierarchy of models in one single table. The API of such models is
+aware of the hierarchy and encapsulates some common needs. For example, given
+these classes:
+
+```ruby
+# app/models/polygon.rb
+class Polygon < ActiveRecord::Base
+end
+
+# app/models/triangle.rb
+class Triangle < Polygon
+end
+
+# app/models/rectangle.rb
+class Rectangle < Polygon
+end
+```
+
+`Triangle.create` creates a row that represents a triangle, and
+`Rectangle.create` creates a row that represents a rectangle. If `id` is the
+ID of an existing record, `Polygon.find(id)` returns an object of the correct
+type.
+
+Methods that operate on collections are also aware of the hierarchy. For
+example, `Polygon.all` returns all the records of the table, because all
+rectangles and triangles are polygons. Active Record takes care of returning
+instances of their corresponding class in the result set.
+
+Types are autoloaded as needed. For example, if `Polygon.first` is a rectangle
+and `Rectangle` has not yet been loaded, Active Record autoloads it and the
+record is correctly instantiated.
+
+All good, but if instead of performing queries based on the root class we need
+to work on some subclass, things get interesting.
+
+While working with `Polygon` you do not need to be aware of all its descendants,
+because anything in the table is by definition a polygon, but when working with
+subclasses Active Record needs to be able to enumerate the types it is looking
+for. Let’s see an example.
+
+`Rectangle.all` only loads rectangles by adding a type constraint to the query:
+
+```sql
+SELECT "polygons".* FROM "polygons"
+WHERE "polygons"."type" IN ("Rectangle")
+```
+
+Let’s introduce now a subclass of `Rectangle`:
+
+```ruby
+# app/models/square.rb
+class Square < Rectangle
+end
+```
+
+`Rectangle.all` should now return rectangles **and** squares:
+
+```sql
+SELECT "polygons".* FROM "polygons"
+WHERE "polygons"."type" IN ("Rectangle", "Square")
+```
+
+But there’s a caveat here: How does Active Record know that the class `Square`
+exists at all?
+
+Even if the file `app/models/square.rb` exists and defines the `Square` class,
+if no code yet used that class, `Rectangle.all` issues the query
+
+```sql
+SELECT "polygons".* FROM "polygons"
+WHERE "polygons"."type" IN ("Rectangle")
+```
+
+That is not a bug, the query includes all *known* descendants of `Rectangle`.
+
+A way to ensure this works correctly regardless of the order of execution is to
+load the leaves of the tree by hand at the bottom of the file that defines the
+root class:
+
+```ruby
+# app/models/polygon.rb
+class Polygon < ActiveRecord::Base
+end
+require_dependency ‘square’
+```
+
+Only the leaves that are **at least grandchildren** need to be loaded this
+way. Direct subclasses do not need to be preloaded. If the hierarchy is
+deeper, intermediate classes will be autoloaded recursively from the bottom
+because their constant will appear in the class definitions as superclass.
+
+### Autoloading and `require`
+
+Files defining constants to be autoloaded should never be `require`d:
+
+```ruby
+require 'user' # DO NOT DO THIS
+
+class UsersController < ApplicationController
+ ...
+end
+```
+
+There are two possible gotchas here in development mode:
+
+1. If `User` is autoloaded before reaching the `require`, `app/models/user.rb`
+runs again because `load` does not update `$LOADED_FEATURES`.
+
+2. If the `require` runs first Rails does not mark `User` as an autoloaded
+constant and changes to `app/models/user.rb` aren't reloaded.
+
+Just follow the flow and use constant autoloading always, never mix
+autoloading and `require`. As a last resort, if some file absolutely needs to
+load a certain file use `require_dependency` to play nice with constant
+autoloading. This option is rarely needed in practice, though.
+
+Of course, using `require` in autoloaded files to load ordinary 3rd party
+libraries is fine, and Rails is able to distinguish their constants, they are
+not marked as autoloaded.
+
+### Autoloading and Initializers
+
+Consider this assignment in `config/initializers/set_auth_service.rb`:
+
+```ruby
+AUTH_SERVICE = if Rails.env.production?
+ RealAuthService
+else
+ MockedAuthService
+end
+```
+
+The purpose of this setup would be that the application uses the class that
+corresponds to the environment via `AUTH_SERVICE`. In development mode
+`MockedAuthService` gets autoloaded when the initializer runs. Let’s suppose
+we do some requests, change its implementation, and hit the application again.
+To our surprise the changes are not reflected. Why?
+
+As [we saw earlier](#constant-reloading), Rails removes autoloaded constants,
+but `AUTH_SERVICE` stores the original class object. Stale, non-reachable
+using the original constant, but perfectly functional.
+
+The following code summarizes the situation:
+
+```ruby
+class C
+ def quack
+ 'quack!'
+ end
+end
+
+X = C
+Object.instance_eval { remove_const(:C) }
+X.new.quack # => quack!
+X.name # => C
+C # => uninitialized constant C (NameError)
+```
+
+Because of that, it is not a good idea to autoload constants on application
+initialization.
+
+In the case above we could implement a dynamic access point:
+
+```ruby
+# app/models/auth_service.rb
+class AuthService
+ if Rails.env.production?
+ def self.instance
+ RealAuthService
+ end
+ else
+ def self.instance
+ MockedAuthService
+ end
+ end
+end
+```
+
+and have the application use `AuthService.instance` instead. `AuthService`
+would be loaded on demand and be autoload-friendly.
+
+### `require_dependency` and Initializers
+
+As we saw before, `require_dependency` loads files in an autoloading-friendly
+way. Normally, though, such a call does not make sense in an initializer.
+
+One could think about doing some [`require_dependency`](#require-dependency)
+calls in an initializer to make sure certain constants are loaded upfront, for
+example as an attempt to address the [gotcha with STIs](#autoloading-and-sti).
+
+Problem is, in development mode [autoloaded constants are wiped](#constant-reloading)
+if there is any relevant change in the file system. If that happens then
+we are in the very same situation the initializer wanted to avoid!
+
+Calls to `require_dependency` have to be strategically written in autoloaded
+spots.
+
+### When Constants aren't Missed
+
+Let's consider an `Image` model, superclass of `Hotel::Image`:
+
+```ruby
+# app/models/image.rb
+class Image
+end
+
+# app/models/hotel/image.rb
+module Hotel
+ class Image < Image
+ end
+end
+```
+
+No matter which file is interpreted first, `app/models/hotel/image.rb` is
+well-defined.
+
+Now consider a third file with this apparently harmless code:
+
+```ruby
+# app/models/hotel/poster.rb
+module Hotel
+ class Poster < Image
+ end
+end
+```
+
+The intention is to subclass `Hotel::Image`, but which is actually the
+superclass of `Hotel::Poster`? Well, it depends on the order of execution:
+
+1. If neither `app/models/image.rb` nor `app/models/hotel/image.rb` have been
+loaded at that point, the superclass is `Hotel::Image` because Rails is told
+`Hotel` is missing a constant called "Image" and loads
+`app/models/hotel/image.rb`. Good.
+
+2. If `app/models/hotel/image.rb` has been loaded at that point, the superclass
+is `Hotel::Image` because Ruby is able to resolve the constant. Good.
+
+3. Lastly, if only `app/models/image.rb` has been loaded so far, the superclass
+is `Image`. Gotcha!
+
+The last scenario (3) may be surprising. Why isn't `Hotel::Image` autoloaded?
+Because Ruby is able to resolve `Image` as a top-level constant, so
+autoloading does not even get a chance.
+
+Most of the time, these kind of ambiguities can be resolved using qualified
+constants. In this case we would write
+
+```ruby
+module Hotel
+ class Poster < Hotel::Image
+ end
+end
+```
+
+That class definition now is robust.
+
+It is interesting to note here that the fix works because `Hotel` is a module, and
+`Hotel::Image` won’t look for `Image` in `Object` as it would if `Hotel` was a
+class with `Object` in its ancestors. If `Hotel` was a class we would resort to
+loading `Hotel::Image` with `require_dependency`. Furthermore, with that
+solution the qualified name would no longer be necessary.
+
+### Autoloading within Singleton Classes
+
+Let's suppose we have these class definitions:
+
+```ruby
+# app/models/hotel/services.rb
+module Hotel
+ class Services
+ end
+end
+
+# app/models/hotel/geo_location.rb
+module Hotel
+ class GeoLocation
+ class << self
+ Services
+ end
+ end
+end
+```
+
+If `Hotel::Services` is known by the time `app/models/hotel/geo_location.rb`
+is being loaded, `Services` is resolved by Ruby because `Hotel` belongs to the
+nesting when the singleton class of `Hotel::GeoLocation` is opened.
+
+But if `Hotel::Services` is not known, Rails is not able to autoload it, the
+application raises `NameError`.
+
+The reason is that autoloading is triggered for the singleton class, which is
+anonymous, and as [we saw before](#generic-procedure), Rails only checks the
+top-level namespace in that edge case.
+
+An easy solution to this caveat is to qualify the constant:
+
+```ruby
+module Hotel
+ class GeoLocation
+ class << self
+ Hotel::Services
+ end
+ end
+end
+```
+
+### Autoloading in `BasicObject`
+
+Direct descendants of `BasicObject` do not have `Object` among their ancestors
+and cannot resolve top-level constants:
+
+```ruby
+class C < BasicObject
+ String # NameError: uninitialized constant C::String
+end
+```
+
+When autoloading is involved that plot has a twist. Let's consider:
+
+```ruby
+class C < BasicObject
+ def user
+ User # WRONG
+ end
+end
+```
+
+Since Rails checks the top-level namespace `User` gets autoloaded just fine the
+first time the `user` method is invoked. You only get the exception if the
+`User` constant is known at that point, in particular in a *second* call to
+`user`:
+
+```ruby
+c = C.new
+c.user # surprisingly fine, User
+c.user # NameError: uninitialized constant C::User
+```
+
+because it detects a parent namespace already has the constant (see [Qualified
+References](#qualified-references).)
+
+As with pure Ruby, within the body of a direct descendant of `BasicObject` use
+always absolute constant paths:
+
+```ruby
+class C < BasicObject
+ ::String # RIGHT
+
+ def user
+ ::User # RIGHT
+ end
+end
+```
diff --git a/guides/source/documents.yaml b/guides/source/documents.yaml
index 1b838201cc..0c0e18288c 100644
--- a/guides/source/documents.yaml
+++ b/guides/source/documents.yaml
@@ -122,6 +122,10 @@
work_in_progress: true
url: initialization.html
description: This guide explains the internals of the Rails initialization process as of Rails 4
+ -
+ name: Constant Autoloading and Reloading
+ url: constant_autoloading_and_reloading.html
+ description: This guide documents how constant autoloading and reloading work.
-
name: Extending Rails
documents:
diff --git a/guides/source/getting_started.md b/guides/source/getting_started.md
index dc63ae62b1..31f78ba11c 100644
--- a/guides/source/getting_started.md
+++ b/guides/source/getting_started.md
@@ -90,18 +90,18 @@ current version of Ruby installed:
TIP: A number of tools exist to help you quickly install Ruby and Ruby
on Rails on your system. Windows users can use [Rails Installer](http://railsinstaller.org),
while Mac OS X users can use [Tokaido](https://github.com/tokaido/tokaidoapp).
+For more installation methods for most Operating Systems take a look at
+[ruby-lang.org](https://www.ruby-lang.org/en/documentation/installation/).
```bash
$ ruby -v
ruby 2.0.0p353
```
-If you don't have Ruby installed have a look at
-[ruby-lang.org](https://www.ruby-lang.org/en/installation/) for possible ways to
-install Ruby on your platform.
-
-Many popular UNIX-like OSes ship with an acceptable version of SQLite3. Windows
-users and others can find installation instructions at the [SQLite3 website](https://www.sqlite.org).
+Many popular UNIX-like OSes ship with an acceptable version of SQLite3.
+On Windows, if you installed Rails through Rails Installer, you
+already have SQLite installed. Others can find installation instructions
+at the [SQLite3 website](https://www.sqlite.org).
Verify that it is correctly installed and in your PATH:
```bash
@@ -422,12 +422,12 @@ If you refresh <http://localhost:3000/articles/new> now, you'll get a new error:
This error indicates that Rails cannot find the `new` action inside the
`ArticlesController` that you just generated. This is because when controllers
are generated in Rails they are empty by default, unless you tell it
-your wanted actions during the generation process.
+your desired actions during the generation process.
To manually define an action inside a controller, all you need to do is to
define a new method inside the controller. Open
`app/controllers/articles_controller.rb` and inside the `ArticlesController`
-class, define a `new` method so that the controller now looks like this:
+class, define the `new` method so that your controller now looks like this:
```ruby
class ArticlesController < ApplicationController
@@ -444,23 +444,23 @@ With the `new` method defined in `ArticlesController`, if you refresh
You're getting this error now because Rails expects plain actions like this one
to have views associated with them to display their information. With no view
-available, Rails errors out.
+available, Rails will raise an exception.
In the above image, the bottom line has been truncated. Let's see what the full
-thing looks like:
+error message looks like:
>Missing template articles/new, application/new with {locale:[:en], formats:[:html], handlers:[:erb, :builder, :coffee]}. Searched in: * "/path/to/blog/app/views"
That's quite a lot of text! Let's quickly go through and understand what each
-part of it does.
+part of it means.
-The first part identifies what template is missing. In this case, it's the
+The first part identifies which template is missing. In this case, it's the
`articles/new` template. Rails will first look for this template. If not found,
then it will attempt to load a template called `application/new`. It looks for
one here because the `ArticlesController` inherits from `ApplicationController`.
The next part of the message contains a hash. The `:locale` key in this hash
-simply indicates what spoken language template should be retrieved. By default,
+simply indicates which spoken language template should be retrieved. By default,
this is the English - or "en" - template. The next key, `:formats` specifies the
format of template to be served in response. The default format is `:html`, and
so Rails is looking for an HTML template. The final key, `:handlers`, is telling
@@ -473,14 +473,16 @@ Templates within a basic Rails application like this are kept in a single
location, but in more complex applications it could be many different paths.
The simplest template that would work in this case would be one located at
-`app/views/articles/new.html.erb`. The extension of this file name is key: the
-first extension is the _format_ of the template, and the second extension is the
-_handler_ that will be used. Rails is attempting to find a template called
-`articles/new` within `app/views` for the application. The format for this
-template can only be `html` and the handler must be one of `erb`, `builder` or
-`coffee`. Because you want to create a new HTML form, you will be using the `ERB`
-language. Therefore the file should be called `articles/new.html.erb` and needs
-to be located inside the `app/views` directory of the application.
+`app/views/articles/new.html.erb`. The extension of this file name is important:
+the first extension is the _format_ of the template, and the second extension
+is the _handler_ that will be used. Rails is attempting to find a template
+called `articles/new` within `app/views` for the application. The format for
+this template can only be `html` and the handler must be one of `erb`,
+`builder` or `coffee`. Because you want to create a new HTML form, you will be
+using the `ERB` language which is designed to embed Ruby in HTML.
+
+Therefore the file should be called `articles/new.html.erb` and needs to be
+located inside the `app/views` directory of the application.
Go ahead now and create a new file at `app/views/articles/new.html.erb` and
write this content in it:
@@ -665,8 +667,8 @@ rake commands to run migrations, and it's possible to undo a migration after
it's been applied to your database. Migration filenames include a timestamp to
ensure that they're processed in the order that they were created.
-If you look in the `db/migrate/20140120191729_create_articles.rb` file (remember,
-yours will have a slightly different name), here's what you'll find:
+If you look in the `db/migrate/YYYYMMDDHHMMSS_create_articles.rb` file
+(remember, yours will have a slightly different name), here's what you'll find:
```ruby
class CreateArticles < ActiveRecord::Migration
@@ -675,7 +677,7 @@ class CreateArticles < ActiveRecord::Migration
t.string :title
t.text :text
- t.timestamps
+ t.timestamps null: false
end
end
end
@@ -736,7 +738,7 @@ database columns. In the first line we do just that (remember that
`@article.save` is responsible for saving the model in the database. Finally,
we redirect the user to the `show` action, which we'll define later.
-TIP: You might be wondering why the `A` in `Article.new` is capitalized above, whereas most other references to articles in this guide have used lowercase. In this context, we are referring to the class named `Article` that is defined in `\models\article.rb`. Class names in Ruby must begin with a capital letter.
+TIP: You might be wondering why the `A` in `Article.new` is capitalized above, whereas most other references to articles in this guide have used lowercase. In this context, we are referring to the class named `Article` that is defined in `app/models/article.rb`. Class names in Ruby must begin with a capital letter.
TIP: As we'll see later, `@article.save` returns a boolean indicating whether
the article was saved or not.
@@ -1537,7 +1539,7 @@ class CreateComments < ActiveRecord::Migration
# this line adds an integer column called `article_id`.
t.references :article, index: true
- t.timestamps
+ t.timestamps null: false
end
end
end
diff --git a/guides/source/layouts_and_rendering.md b/guides/source/layouts_and_rendering.md
index ae16ad86cd..28fa61a964 100644
--- a/guides/source/layouts_and_rendering.md
+++ b/guides/source/layouts_and_rendering.md
@@ -904,7 +904,10 @@ You can also specify multiple videos to play by passing an array of videos to th
This will produce:
```erb
-<video><source src="/videos/trailer.ogg" /><source src="/videos/trailer.flv" /></video>
+<video>
+ <source src="/videos/trailer.ogg">
+ <source src="/videos/movie.ogg">
+</video>
```
#### Linking to Audio Files with the `audio_tag`
diff --git a/guides/source/security.md b/guides/source/security.md
index b1c5b22338..b3869b1ba5 100644
--- a/guides/source/security.md
+++ b/guides/source/security.md
@@ -942,7 +942,7 @@ unless params[:token].nil?
end
```
-When `params[:token]` is one of: `[]`, `[nil]`, `[nil, nil, ...]` or
+When `params[:token]` is one of: `[nil]`, `[nil, nil, ...]` or
`['foo', nil]` it will bypass the test for `nil`, but `IS NULL` or
`IN ('foo', NULL)` where clauses still will be added to the SQL query.
@@ -953,9 +953,9 @@ request:
| JSON | Parameters |
|-----------------------------------|--------------------------|
| `{ "person": null }` | `{ :person => nil }` |
-| `{ "person": [] }` | `{ :person => nil }` |
-| `{ "person": [null] }` | `{ :person => nil }` |
-| `{ "person": [null, null, ...] }` | `{ :person => nil }` |
+| `{ "person": [] }` | `{ :person => [] }` |
+| `{ "person": [null] }` | `{ :person => [] }` |
+| `{ "person": [null, null, ...] }` | `{ :person => [] }` |
| `{ "person": ["foo", null] }` | `{ :person => ["foo"] }` |
It is possible to return to old behaviour and disable `deep_munge` configuring
diff --git a/guides/source/upgrading_ruby_on_rails.md b/guides/source/upgrading_ruby_on_rails.md
index 8cb0945b52..7ef51b6dc0 100644
--- a/guides/source/upgrading_ruby_on_rails.md
+++ b/guides/source/upgrading_ruby_on_rails.md
@@ -207,12 +207,47 @@ gem 'rails-deprecated_sanitizer'
```
### Rails DOM Testing
+
The [`TagAssertions` module](http://api.rubyonrails.org/classes/ActionDispatch/Assertions/TagAssertions.html) (containing methods such as `assert_tag`), [has been deprecated](https://github.com/rails/rails/blob/6061472b8c310158a2a2e8e9a6b81a1aef6b60fe/actionpack/lib/action_dispatch/testing/assertions/dom.rb) in favor of the `assert_select` methods from the `SelectorAssertions` module, which has been extracted into the [rails-dom-testing gem](https://github.com/rails/rails-dom-testing).
### Masked Authenticity Tokens
+
In order to mitigate SSL attacks, `form_authenticity_token` is now masked so that it varies with each request. Thus, tokens are validated by unmasking and then decrypting. As a result, any strategies for verifying requests from non-rails forms that relied on a static session CSRF token have to take this into account.
+### Action Mailer
+
+Previously, calling a mailer method on a mailer class will result in the
+corresponding instance method being executed directly. With the introduction of
+Active Job and `#deliver_later`, this is no longer true. In Rails 4.2, the
+invocation of the instance methods are deferred until either `deliver_now` or
+`deliver_later` is called. For example:
+
+```ruby
+class Notifier < ActionMailer::Base
+ def notify(user, ...)
+ puts "Called"
+ mail(to: user.email, ...)
+ end
+end
+
+mail = Notifier.notify(user, ...) # Notifier#notify is not yet called at this point
+mail = mail.deliver_now # Prints "Called"
+```
+
+This should not result in any noticible differnces for most applications.
+However, if you need some non-mailer methods to be exectuted synchronously, and
+you were previously relying on the synchronous proxying behavior, you should
+define them as class methods on the mailer class directly:
+
+```ruby
+class Notifier < ActionMailer::Base
+ def self.broadcast_notifications(users, ...)
+ users.each { |user| Notifier.notify(user, ...) }
+ end
+end
+```
+
Upgrading from Rails 4.0 to Rails 4.1
-------------------------------------
@@ -915,10 +950,6 @@ Also check your environment settings for `config.action_dispatch.best_standards_
Rails 4.0 removes the `j` alias for `ERB::Util#json_escape` since `j` is already used for `ActionView::Helpers::JavaScriptHelper#escape_javascript`.
-#### Cache
-
-The caching method changed between Rails 3.x and 4.0. You should [change the cache namespace](http://guides.rubyonrails.org/caching_with_rails.html#activesupport-cache-store) and roll out with a cold cache.
-
### Helpers Loading Order
The order in which helpers from more than one directory are loaded has changed in Rails 4.0. Previously, they were gathered and then sorted alphabetically. After upgrading to Rails 4.0, helpers will preserve the order of loaded directories and will be sorted alphabetically only within each directory. Unless you explicitly use the `helpers_path` parameter, this change will only impact the way of loading helpers from engines. If you rely on the ordering, you should check if correct methods are available after upgrade. If you would like to change the order in which engines are loaded, you can use `config.railties_order=` method.
generated by cgit v1.2.3 (git 2.25.1) at 2024-11-07 21:28:13 +0000