[Feature Request + Solution] Add support for nested forms gem like "Cocoon"

[jamesst20]

Hi,

One of the great feature of StoreModel is its compatibility with Rails built in features like accepts_nested_attributes_for.

One bummer is that it won't work with basic gem like https://github.com/nathanvda/cocoon where you can easily have let's say multiple phone numbers with an Add / Trash button because they expect to have an ActiveRecord::Relation but they get a simple Array.

I'm sharing my workaround here but it would be very great to a better/deeper implementation.

Demo usage

class Member < ApplicationRecord
  include StoreModel::NestedAttributes

  attribute :contact, Contact.to_type

  accepts_nested_attributes_for :contact, allow_destroy: true, update_only: true, reject_if: :all_blank

class Contact < ApplicationStoreModel
  attribute :id, :integer
  attribute :name, :string
  attribute :phones, Phone.to_array_type

  accepts_nested_attributes_for :phones, allow_destroy: true, update_only: true, reject_if: :all_blank
end

class Phone < ApplicationStoreModel
  attribute :id, :integer
  attribute :number, :string
  attribute :type_id, :integer
end

app/views/shared/phones/form.html.haml

- model_class = Phone
- partial_fields = "shared/phones/form_fields"

#phones
  = model_class.model_name.human(count: 2)
  = f.simple_fields_for :phones do |ff|
    = render partial_fields, f: ff
  .phones.mb-2
    = link_to_add_association f, :phones, partial: partial_fields, class: "btn btn-outline-secondary my-2"  do
      %i.fas.fa-plus
      = t("helpers.links.add")

app/views/shared/phones/form_fields.html.haml

.nested-fields
  = f.input :number
  = f.input :type_id

  = link_to_remove_association f, class: "btn btn-outline-danger align-self-end" do
    %i.fa-solid.fa-trash

That's it for the Demo. Use cocoon as if everything were standard ActiveRecord model.

Solution / Workaround to get this to work

The trick is to override the phones getter to return an extended Array type that respond to expected methods by Cocoon. The simplest way I got around it is to override the attribute class methods to re-define my getters at the same time. Then i created a base class that I make every StoreModel extends of.

config/initializers/store_model.rb

module CocoonCompatibility
  extend ActiveSupport::Concern

  class ArrayForm < Array
    attr_reader :klass

    def initialize(klass)
      @klass = klass
      super()
    end

    def build
      new_item = klass.new
      push new_item
      new_item
    end
  end

  included do |klass|
    ##
    # Redefine the getter for every StoreModel array type to use the "ArrayForm"
    def self.attribute(name, type = nil, **args)
      super

      return unless type.is_a? StoreModel::Types::Many

      define_method name do
        values = super()

        return values if values.is_a? CocoonCompatibility::ArrayForm

        array = CocoonCompatibility::ArrayForm.new(type.model_klass)
        array.push(*values)
        array
      end
    end

    def self.reflect_on_association(association)
      return nil unless public_method_defined? association

      ActiveRecord::Reflection::HasManyReflection.new(association, nil, {}, OpenStruct.new) # rubocop:disable Style/OpenStructUse
    end

    def new_record?
      id.nil?
    end

    def mark_for_destruction
      @marked_for_destruction = true
    end

    def marked_for_destruction?
      @marked_for_destruction || false
    end

    def _destroy
      marked_for_destruction?
    end
  end
end

class ApplicationStoreModel
  include StoreModel::Model
  include StoreModel::NestedAttributes

  include Draper::Decoratable # If you use the draper gem, this works.

  include CocoonCompatibility
end

[DmitryTsepelev]

Hey hey! Frankly speaking I've never heard of a cocoon 😅anyway, having some modules to optionally mix them in to make the gem work with something else sounds good to me, I'd be happy to merge something like this