1
0
Fork 0
mirror of https://github.com/rails/rails.git synced 2022-11-09 12:12:34 -05:00
rails--rails/guides/source/nested_model_forms.textile
2012-03-17 08:32:49 -07:00

222 lines
6.7 KiB
Text
Raw Blame History

This file contains ambiguous Unicode characters

This file contains Unicode characters that might be confused with other characters. If you think that this is intentional, you can safely ignore this warning. Use the Escape button to reveal them.

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, its *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 _dont_ 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]" 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]" type="text" />
<input id="person_address_attributes_street" name="person[address_attributes][street]" 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>
Thats 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]" type="text" />
<input id="person_projects_attributes_0_name" name="person[projects_attributes][0][name]" type="text" />
<input id="person_projects_attributes_1_name" name="person[projects_attributes][1][name]" 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.