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https://github.com/m-peter/activeform

Create nested forms with ease.
https://github.com/m-peter/activeform

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Create nested forms with ease.

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README 

        
# Active Form



[![Build Status](https://api.travis-ci.org/rails/activeform.svg?branch=master)](https://travis-ci.org/rails/activeform)



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.



## Installation



Add this line to your `Gemfile`:



```ruby

gem 'active_form'

```



## Defining Forms



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`:



```ruby

class ConferenceForm < ActiveForm::Base

  self.main_model = :conference



  attributes :name, :city



  validates :name, :city, presence: true

end

```



Your 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:



```ruby

self.main_model = :conference

```



To 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:



```ruby

class ConferenceForm < ActiveForm::Base

  attributes :name, :city, required: true

end

```



## The API



The `ActiveForm::Base` class provides a simple API with only a few instance/class methods. Below are listed the instance methods:



1. `initialize(model)` accepts an instance of the model that the form represents.

2. `submit(params)` updates the main form's model and nested models with the posted parameters. The models are not saved/updated until you call `save`.

3. `errors` returns validation messages in a classy Active Model style.

4. `save` will call `save` on 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:



1. `attributes` accepts 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 the `required: true` option as showcased above. The `attribute` method is aliased to the `attributes` method.

2. `association(name, options={}, &block)` defines a nested form for the `name` model. If the model is a `has_many` association you can pass in the `records: x` option and fields to create `x` objects 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.



## Setup



In your controller you create a form instance and pass in the model you want to work on.



```ruby

class ConferencesController

  def new

    conference = Conference.new

    @conference_form = ConferenceForm.new(conference)

  end

end

```



You can also setup the form for editing existing items.



```ruby

class ConferencesController

  def edit

    conference = Conference.find(params[:id])

    @conference_form = ConferenceForm.new(conference)

  end

end

```



Active Form will read property values from the model in setup. Given the following form class.



```ruby

class ConferenceForm < ActiveForm::Base

  attribute :name

end

```



Internally, this form will call `conference.name` to populate the name field.



## Rendering Forms



Your `@conference_form` is now ready to be rendered, either do it yourself or use something like Rails' `form_for`, `simple_form` or `formtastic`.



```erb

<%= 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.



## Syncing Back



After setting up your form object, you can populate the models with the submitted parameters.



```ruby

class ConferencesController

  def create

    conference = Conference.new

    @conference_form = ConferenceForm.new(conference)

    @conference_form.submit(conference_params)

  end

end

```



This will write all the properties back to the model. In a nested form, this works recursively, of course.



## Saving Forms



After the form is populated with the posted data, you can save the model by calling `save`.



```ruby

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

end

```



If 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.



## Nesting Forms: 1-n Relations



Active Form also gives you nested collections.



Let's define the `has_many :speakers` collection association on the `Conference` model.



```ruby

class Conference < ActiveRecord::Base

  has_many :speakers

  validates :name, uniqueness: true

end

```



The form should look like this.



```ruby

class ConferenceForm < ActiveForm::Base

  attributes :name, :city, required: true



  association :speakers do

    attributes :name, :occupation, required: true

  end

end

```



By 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.



### has_many: Rendering



Active Form will expose the collection using the `speakers` method.



```erb

<%= 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 %>

```



## Nesting Forms: 1-1 Relations



Speakers are allowed to have 1 Presentation.



```ruby

class Speaker < ActiveRecord::Base

  has_one :presentation

  belongs_to :conference

  validates :name, uniqueness: true

end

```



The full form should look like this:



```ruby

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

end

```



### has_one: Rendering



Use `fields_for` in a Rails environment to correctly setup the structure of params.



```erb

<%= 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 %>

```



## Dynamically Adding/Removing Nested Objects



Active Form comes with two helpers to deal with this functionality:



1. `link_to_add_association` will display a link that renders fields to create a new object.

2. `link_to_remove_association` will 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:



```erb

<%= form_for @conference_form do |f| %>

  <% if @conference_form.errors.any? %>

    


      
<%= pluralize(@conference_form.errors.count, "error") %> prohibited this conference from being saved:



      
    

          <% @conference_form.errors.full_messages.each do |message| %>

            
  • <%= message %>
    • 

          <% end %>

          


    


  <% end %>



  
Conference Details


  


    <%= f.label :name, "Conference Name" %>


    <%= f.text_field :name %>

  


  


    <%= f.label :city %>


    <%= f.text_field :city %>

  



  
Speaker Details


  <%= f.fields_for :speakers do |speaker_fields| %>

    <%= render "speaker_fields", :f => speaker_fields %>

  <% end %>



  


    <%= link_to_add_association "Add a Speaker", f, :speakers %>

  



  


    <%= f.submit %>

  


<% end %>

```



Our `app/views/conferences/_speaker_fields.html.erb` would be:



```erb



  


    <%= f.label :name, "Speaker Name" %>


    <%= f.text_field :name %>

  



  


    <%= f.label :occupation %>


    <%= f.text_field :occupation %>

  



  
Presentantions


  <%= f.fields_for :presentation do |presentations_fields| %>

    <%= render "presentation_fields", :f => presentations_fields %>

  <% end %>



  <%= link_to_remove_association "Delete", f %>



```



And `app/views/conferences/_presentation_fields.html.erb` would be:



```erb



  <%= f.label :topic %>


  <%= f.text_field :topic %>






  <%= f.label :duration %>


  <%= f.text_field :duration %>



```



## Plain Old Ruby Object Forms



ActiveForm also can accept `ActiveModel::Model` instances as a model.



```ruby

class Feedback

  include ActiveModel::Model



  attr_accessible :name, :body, :email



  def save

    FeedbackMailer.send_email(email, name, body)

  end

end

```



The form should look like this.



```ruby

class FeedbackForm < ActiveForm::Base

  attributes :name, :body, :email, required: true

end

```



And then in controller:



```ruby

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

  end

```



## Demos



You 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.



## Credits



Special thanks to the owners of the great gems that inspired this work:



* [Nick Sutterer](https://github.com/apotonick) - creator of [reform](https://github.com/apotonick/reform)

* [Nathan Van der Auwera](https://github.com/nathanvda) - creator of [cocoon](https://github.com/nathanvda/cocoon)