Bring abstract_controller up to date with rails/master

Resolved all the conflicts since 2.3.0 -> HEAD. Following is a list
of commits that could not be applied cleanly or are obviated with the
abstract_controller refactor. They all need to be revisited to ensure
that fixes made in 2.3 do not reappear in 3.0:

2259ecf368e6a6715966f69216e3ee86bf1a82a7
AR not available
  * This will be reimplemented with ActionORM or equivalent

06182ea02e92afad579998aa80144588e8865ac3
implicitly rendering a js response should not use the default layout
[#1844 state:resolved]
  * This will be handled generically

893e9eb99504705419ad6edac14d00e71cef5f12
Improve view rendering performance in development mode and reinstate
template recompiling in production [#1909 state:resolved]
  * We will need to reimplement rails-dev-boost on top of the refactor;
    the changes here are very implementation specific and cannot be
    cleanly applied. The following commits are implicated:

      199e750d46c04970b5e7684998d09405648ecbd4
      3942cb406e1d5db0ac00e03153809cc8dc4cc4db
      f8ea9f85d4f1e3e6f3b5d895bef6b013aa4b0690
      e3b166aab37ddc2fbab030b146eb61713b91bf55
      ae9f258e03c9fd5088da12c1c6cd216cc89a01f7
      44423126c6f6133a1d9cf1d0832b527e8711d40f

0cb020b4d6d838025859bd60fb8151c8e21b8e84
workaround for picking layouts based on wrong view_paths
[#1974 state:resolved]
  * The specifics of this commit no longer apply. Since it is a two-line
    commit, we will reimplement this change.

8c5cc66a831aadb159f3daaffa4208064c30af0e
make action_controller/layouts pick templates from the current instance's
view_paths instead of the class view_paths [#1974 state:resolved]
  * This does not apply at all. It should be trivial to apply the feature
    to the reimplemented ActionController::Base.

87e8b162463f13bd50d27398f020769460a770e3
fix HTML fallback for explicit templates [#2052 state:resolved]
  * There were a number of patches related to this that simply compounded
    each other. Basically none of them apply cleanly, and the underlying
    issue needs to be revisited. After discussing the underlying problem
    with Koz, we will defer these fixes for further discussion.

1 files changed, 222 insertions, 0 deletions

diff --git a/railties/guides/source/nested_model_forms.textile b/railties/guides/source/nested_model_forms.textile
new file mode 100644
index 0000000000..4b685b214e
--- /dev/null
+++ b/railties/guides/source/nested_model_forms.textile
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+h2. Rails nested model forms
+
+Creating a form for a model _and_ its associations can become quite tedious. Therefor Rails provides helpers to assist in dealing with the complexities of generating these forms _and_ the required CRUD operations to create, update, and destroy associations.
+
+In this guide you will:
+
+* do stuff
+
+endprologue.
+
+NOTE: This guide assumes the user knows how to use the "Rails form helpers":form_helpers.html in general. Also, it’s *not* an API reference. For a complete reference please visit "the Rails API documentation":http://api.rubyonrails.org/.
+
+
+h3. Model setup
+
+To be able to use the nested model functionality in your forms, the model will need to support some basic operations.
+
+First of all, it needs to define a writer method for the attribute that corresponds to the association you are building a nested model form for. The +fields_for+ form helper will look for this method to decide whether or not a nested model form should be build.
+
+If the associated object is an array a form builder will be yielded for each object, else only a single form builder will be yielded.
+
+Consider a Person model with an associated Address. When asked to yield a nested FormBuilder for the +:address+ attribute, the +fields_for+ form helper will look for a method on the Person instance named +address_attributes=+.
+
+h4. ActiveRecord::Base model
+
+For an ActiveRecord::Base model and association this writer method is commonly defined with the +accepts_nested_attributes_for+ class method:
+
+h5. has_one
+
+<ruby>
+class Person < ActiveRecord::Base
+  has_one :address
+  accepts_nested_attributes_for :address
+end
+</ruby>
+
+h5. belongs_to
+
+<ruby>
+class Person < ActiveRecord::Base
+  belongs_to :firm
+  accepts_nested_attributes_for :firm
+end
+</ruby>
+
+h5. has_many / has_and_belongs_to_many
+
+<ruby>
+class Person < ActiveRecord::Base
+  has_many :projects
+  accepts_nested_attributes_for :projects
+end
+</ruby>
+
+h4. Custom model
+
+As you might have inflected from this explanation, you _don’t_ necessarily need an ActiveRecord::Base model to use this functionality. The following examples are sufficient to enable the nested model form behaviour:
+
+h5. Single associated object
+
+<ruby>
+class Person
+  def address
+    Address.new
+  end
+  
+  def address_attributes=(attributes)
+    # ...
+  end
+end
+</ruby>
+
+h5. Association collection
+
+<ruby>
+class Person
+  def projects
+    [Project.new, Project.new]
+  end
+  
+  def projects_attributes=(attributes)
+    # ...
+  end
+end
+</ruby>
+
+NOTE: See (TODO) in the advanced section for more information on how to deal with the CRUD operations in your custom model.
+
+h3. Views
+
+h4. Controller code
+
+A nested model form will _only_ be build if the associated object(s) exist. This means that for a new model instance you would probably want to build the associated object(s) first.
+
+Consider the following typical RESTful controller which will prepare a new Person instance and its +address+ and +projects+ associations before rendering the +new+ template:
+
+<ruby>
+class PeopleController < ActionController:Base
+  def new
+    @person = Person.new
+    @person.built_address
+    2.times { @person.projects.build }
+  end
+  
+  def create
+    @person = Person.new(params[:person])
+    if @person.save
+      # ...
+    end
+  end
+end
+</ruby>
+
+NOTE: Obviously the instantiation of the associated object(s) can become tedious and not DRY, so you might want to move that into the model itself. ActiveRecord::Base provides an +after_initialize+ callback which is a good way to refactor this.
+
+h4. Form code
+
+Now that you have a model instance, with the appropriate methods and associated object(s), you can start building the nested model form.
+
+h5. Standard form
+
+Start out with a regular RESTful form:
+
+<erb>
+<% form_for @person do |f| %>
+  <%= f.text_field :name %>
+<% end %>
+</erb>
+
+This will generate the following html:
+
+<html>
+<form action="/people" class="new_person" id="new_person" method="post">
+  <input id="person_name" name="person[name]" size="30" type="text" />
+</form>
+</html>
+
+h5. Nested form for a single associated object
+
+Now add a nested form for the +address+ association:
+
+<erb>
+<% form_for @person do |f| %>
+  <%= f.text_field :name %>
+  
+  <% f.fields_for :address do |af| %>
+    <%= f.text_field :street %>
+  <% end %>
+<% end %>
+</erb>
+
+This generates:
+
+<html>
+<form action="/people" class="new_person" id="new_person" method="post">
+  <input id="person_name" name="person[name]" size="30" type="text" />
+  
+  <input id="person_address_attributes_street" name="person[address_attributes][street]" size="30" type="text" />
+</form>
+</html>
+
+Notice that +fields_for+ recognized the +address+ as an association for which a nested model form should be build by the way it has namespaced the +name+ attribute.
+
+When this form is posted the Rails parameter parser will construct a hash like the following:
+
+<ruby>
+{
+  "person" => {
+    "name" => "Eloy Duran",
+    "address_attributes" => {
+      "street" => "Nieuwe Prinsengracht"
+    }
+  }
+}
+</ruby>
+
+That’s it. The controller will simply pass this hash on to the model from the +create+ action. The model will then handle building the +address+ association for you and automatically save it when the parent (+person+) is saved.
+
+h5. Nested form for a collection of associated objects
+
+The form code for an association collection is pretty similar to that of a single associated object:
+
+<erb>
+<% form_for @person do |f| %>
+  <%= f.text_field :name %>
+  
+  <% f.fields_for :projects do |pf| %>
+    <%= f.text_field :name %>
+  <% end %>
+<% end %>
+</erb>
+
+Which generates:
+
+<html>
+<form action="/people" class="new_person" id="new_person" method="post">
+  <input id="person_name" name="person[name]" size="30" type="text" />
+  
+  <input id="person_projects_attributes_0_name" name="person[projects_attributes][0][name]" size="30" type="text" />
+  <input id="person_projects_attributes_1_name" name="person[projects_attributes][1][name]" size="30" type="text" />
+</form>
+</html>
+
+As you can see it has generated 2 +project name+ inputs, one for each new +project+ that’s build in the controllers +new+ action. Only this time the +name+ attribute of the input contains a digit as an extra namespace. This will be parsed by the Rails parameter parser as:
+
+<ruby>
+{
+  "person" => {
+    "name" => "Eloy Duran",
+    "projects_attributes" => {
+      "0" => { "name" => "Project 1" },
+      "1" => { "name" => "Project 2" }
+    }
+  }
+}
+</ruby>
+
+You can basically see the +projects_attributes+ hash as an array of attribute hashes. One for each model instance.
+
+NOTE: The reason that +fields_for+ constructed a form which would result in a hash instead of an array is that it won't work for any forms nested deeper than one level deep.
+
+TIP: You _can_ however pass an array to the writer method generated by +accepts_nested_attributes_for+ if you're using plain Ruby or some other API access. See (TODO) for more info and example.
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