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-h2. Rails nested model forms
-
-Creating a form for a model _and_ its associations can become quite tedious. Therefore 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 built 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| %>
- <%= af.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 built 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| %>
- <%= pf.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 was built in the controller's +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.