Set your models free from the accepts_nested_attributes_for helper. Active Form provides an object-oriented approach to represent your forms by building a form object, rather than relying on Active Record internals for doing this. Form objects provide an API to describe the models involved in the form, their attributes and validations. A form object deals with create/update actions of nested objects in a more seamless way.
Add this line to your Gemfile:
gem 'active_form'Consider an example where you want to create/update a conference that can have many speakers which can present a single presentation with one form submission. You start by defining a form to represent the root model, Conference:
class ConferenceForm < ActiveForm::Base
self.main_model = :conference
attributes :name, :city
validates :name, :city, presence: true
endYour form object has to subclass ActiveForm::Base in order to gain the necessary API. When defining the form, you have to specify the main_model the form represents with the following line:
self.main_model = :conferenceTo add fields to the form, use the attributes or attribute class method. The form can also define validation rules for the model it represents. For the presence validation rule there is a short inline syntax:
class ConferenceForm < ActiveForm::Base
attributes :name, :city, required: true
endThe ActiveForm::Base class provides a simple API with only a few instance/class methods. Below are listed the instance methods:
initialize(model)accepts an instance of the model that the form represents.submit(params)updates the main form's model and nested models with the posted parameters. The models are not saved/updated until you callsave.errorsreturns validation messages in a classy Active Model style.savewill callsaveon the model and nested models. This method will validate the model and nested models and if no error arises then it will save them and return true.
The following are the class methods:
attributesaccepts the names of attributes to define on the form. If you want to declare a presence validation rule for the given attributes, you can pass in therequired: trueoption as showcased above. Theattributemethod is aliased to theattributesmethod.association(name, options={}, &block)defines a nested form for thenamemodel. If the model is ahas_manyassociation you can pass in therecords: xoption and fields to createxobjects will be rendered. If you pass a block, you can define another nested form the same way.
In addition to the main API, forms expose accessors to the defined attributes. This is used for rendering or manual operations.
In your controller you create a form instance and pass in the model you want to work on.
class ConferencesController
def new
conference = Conference.new
@conference_form = ConferenceForm.new(conference)
end
endYou can also setup the form for editing existing items.
class ConferencesController
def edit
conference = Conference.find(params[:id])
@conference_form = ConferenceForm.new(conference)
end
endActive Form will read property values from the model in setup. Given the following form class.
class ConferenceForm < ActiveForm::Base
attribute :name
endInternally, this form will call conference.name to populate the name field.
Your @conference_form is now ready to be rendered, either do it yourself or use something like Rails' form_for, simple_form or formtastic.
<%= form_for @conference_form do |f| %>
<%= f.text_field :name %>
<%= f.text_field :city %>
<% end %>Nested forms and collections can be easily rendered with fields_for, etc. Just use Active Form as if it would be an Active Model instance in the view layer.
After setting up your form object, you can populate the models with the submitted parameters.
class ConferencesController
def create
conference = Conference.new
@conference_form = ConferenceForm.new(conference)
@conference_form.submit(conference_params)
end
endThis will write all the properties back to the model. In a nested form, this works recursively, of course.
After the form is populated with the posted data, you can save the model by calling save.
class ConferencesController
def create
conference = Conference.new
@conference_form = ConferenceForm.new(conference)
@conference_form.submit(conference_params)
if @conference_form.save
redirect_to @conference_form, notice: "Conference: #{@conference_form.name} was successfully created." }
else
render :new
end
end
endIf the save method returns false due to validation errors defined on the form, you can render it again with the data that has been submitted and the errors found.
Active Form also gives you nested collections.
Let's define the has_many :speakers collection association on the Conference model.
class Conference < ActiveRecord::Base
has_many :speakers
validates :name, uniqueness: true
endThe form should look like this.
class ConferenceForm < ActiveForm::Base
attributes :name, :city, required: true
association :speakers do
attributes :name, :occupation, required: true
end
endBy default, the association :speakers declaration will create a single Speaker object. You can specify how many objects you want in your form to be rendered with the new action as follows: association: speakers, records: 2. This will create 2 new Speaker objects, and of course fields to create 2 Speaker objects. There are also some link helpers to dynamically add/remove objects from collection associations. Read below.
This basically works like a nested property that iterates over a collection of speakers.
Active Form will expose the collection using the speakers method.
<%= form_for @conference_form |f| %>
<%= f.text_field :name %>
<%= f.text_field :city %>
<%= f.fields_for :speakers do |s| %>
<%= s.text_field :name %>
<%= s.text_field :occupation %>
<% end %>
<% end %>Speakers are allowed to have 1 Presentation.
class Speaker < ActiveRecord::Base
has_one :presentation
belongs_to :conference
validates :name, uniqueness: true
endThe full form should look like this:
class ConferenceForm < ActiveForm::Base
attributes :name, :city, required: true
association :speakers do
attribute :name, :occupation, required: true
association :presentation do
attribute :topic, :duration, required: true
end
end
endUse fields_for in a Rails environment to correctly setup the structure of params.
<%= form_for @conference_form |f| %>
<%= f.text_field :name %>
<%= f.text_field :city %>
<%= f.fields_for :speakers do |s| %>
<%= s.text_field :name %>
<%= s.text_field :occupation %>
<%= s.fields_for :presentation do |p| %>
<%= p.text_field :topic %>
<%= p.text_field :duration %>
<% end %>
<% end %>
<% end %>Active Form comes with two helpers to deal with this functionality:
link_to_add_associationwill display a link that renders fields to create a new object.link_to_remove_associationwill display a link to remove a existing/dynamic object.
In order to use it you have to insert this line: //= require active_form to your app/assets/javascript/application.js file.
In our ConferenceForm we can dynamically create/remove Speaker objects. To do that we would write in the app/views/conferences/_form.html.erb partial:
<%= form_for @conference_form do |f| %>
<% if @conference_form.errors.any? %>
<div id="error_explanation">
<h2><%= pluralize(@conference_form.errors.count, "error") %> prohibited this conference from being saved:</h2>
<ul>
<% @conference_form.errors.full_messages.each do |message| %>
<li><%= message %></li>
<% end %>
</ul>
</div>
<% end %>
<h2>Conference Details</h2>
<div class="field">
<%= f.label :name, "Conference Name" %><br>
<%= f.text_field :name %>
</div>
<div class="field">
<%= f.label :city %><br>
<%= f.text_field :city %>
</div>
<h2>Speaker Details</h2>
<%= f.fields_for :speakers do |speaker_fields| %>
<%= render "speaker_fields", :f => speaker_fields %>
<% end %>
<div class="links">
<%= link_to_add_association "Add a Speaker", f, :speakers %>
</div>
<div class="actions">
<%= f.submit %>
</div>
<% end %>Our app/views/conferences/_speaker_fields.html.erb would be:
<div class="nested-fields">
<div class="field">
<%= f.label :name, "Speaker Name" %><br>
<%= f.text_field :name %>
</div>
<div class="field">
<%= f.label :occupation %><br>
<%= f.text_field :occupation %>
</div>
<h2>Presentantions</h2>
<%= f.fields_for :presentation do |presentations_fields| %>
<%= render "presentation_fields", :f => presentations_fields %>
<% end %>
<%= link_to_remove_association "Delete", f %>
</div>And app/views/conferences/_presentation_fields.html.erb would be:
<div class="field">
<%= f.label :topic %><br>
<%= f.text_field :topic %>
</div>
<div class="field">
<%= f.label :duration %><br>
<%= f.text_field :duration %>
</div>ActiveForm also can accept ActiveModel::Model instances as a model.
class Feedback
include ActiveModel::Model
attr_accessible :name, :body, :email
def save
FeedbackMailer.send_email(email, name, body)
end
endThe form should look like this.
class FeedbackForm < ActiveForm::Base
attributes :name, :body, :email, required: true
endAnd then in controller:
class FeedbacksController
def create
feedback = Feedback.new
@feedback_form = FeedbackForm.new(feedback)
@feedback_form.submit(feedback_params)
if @feedback_form.save
head :ok
else
render json: @feedback_form.errors
end
endYou can find a list of applications using this gem in this repository: https://github.com/m-Peter/nested-form-examples .
All the examples are implemented in before/after pairs. The before is using the accepts_nested_attributes_for, while the after uses this gem to achieve the same functionality.
Special thanks to the owners of the great gems that inspired this work:
- Nick Sutterer - creator of reform
- Nathan Van der Auwera - creator of cocoon