Postgres Arrays in Active Admin

active_admin.sass

// app/assets/stylesheets/active_admin.sass

=reset-aa-button
  background: none
  border-radius: 0
  border: 0
  box-shadow: none
  line-height: 1
  padding: 0
  text-shadow: none
  vertical-align: middle
  &:not(.disabled)
    &:hover,
    &:active,
    &:focus
      background: none
      border: 0
      box-shadow: none

.array-action--add,
.array-action--remove
  +reset-aa-button
  font-size: rem(15)

.array-action--add
  color: $alert-success-color

.array-action--remove
  color: $alert-error-color
  &.can-undo
    color: $alert-success-color

array-input.coffee

# app/assets/javascripts/array-input.coffee
$ ->
  removeFromArrayInput = (el) ->
    input = $(el).siblings('input')
    if input.attr('disabled') == 'disabled'
      $(el)
        .html('<i class="fa fa-times-circle"></i>')
        .removeClass('can-undo')
      $(input).removeAttr('disabled')
      $(input).removeClass('text--strike')
    else
      $(el)
        .html('<i class="fa fa-undo"></i>')
        .addClass('can-undo')
      $(input).attr('disabled', 'disabled')
      $(input).addClass('text--strike')

  $('.js-add-to-array-input').click (e) ->
    e.preventDefault

    if $(@).hasClass('array-action--add')
      original = $(@).parent()
      clone    = $(original).clone(true)
      clone_id = "clone_#{Math.floor((Math.random() * 100000) + 1)}"
      input    = $(clone).find('input')

      if $(input).val() != ''
        # Remove error classes from original's input
        $(original)
          .find('input')
          .removeClass('has-error')

        # Reset clone's input
        $(input)
          .removeClass('has-error')
          .attr('id', clone_id)
          .val('')

        # Change action to remove
        $(@)
          .html('<i class="fa fa-times-circle"></i>')
          .attr('class', 'array-action--remove js-remove-from-array-input')

        # Add clone and focus its input
        $(@).parent().parent().append $(clone)
        $("##{clone_id}").focus()

      else
        $(original)
          .find('input')
          .addClass('has-error')
          .focus()

    else
      removeFromArrayInput $(@)

  $('.js-remove-from-array-input').click (e) ->
    e.preventDefault
    removeFromArrayInput $(@)

array_input.rb

# based on https://gist.github.com/kivanio/2fdfaa723350d6e85c1a
class ArrayInput
  include Formtastic::Inputs::Base::Choices
  include Formtastic::Inputs::Base

  def to_html
    input_wrapping do
      inputs = []

      @object[method].each_with_index do |v, x|
        inputs << array_input_html(v)
      end

      choices_wrapping do
        legend_html <<
          choices_group_wrapping do
            template.content_tag(:div, class: 'input-group--array') do
              inputs.join.html_safe << array_input_html('', false)
            end
          end
      end
    end
  end

  private

    def array_input_html(value, remove=true)
      if remove
        button = template.content_tag(:button, template.fa_icon('minus-circle'), class: 'array-action--remove js-remove-from-array-input', type: 'button')
      else
        button = template.content_tag(:button, template.fa_icon('plus-circle'), class: 'array-action--add js-add-to-array-input', type: 'button')
      end
      template.content_tag(:li, class: 'choice input-group--array__item') do
        template.text_field_tag("#{object_name}[#{method}][]", value, id: nil) << button
      end
    end

end

client.rb

# app/admin/client.rb
ActiveAdmin.register Client do

  permit_params email_addresses: []

  form do |f|
    f.inputs 'Contact Details' do
      f.input :email_addresses, as: :array
    end
    f.actions
  end

end

client_model.rb

class Client < ActiveRecord::Base # Used with Mongoid as well.
  def email_addresses=(vals)
    write_attribute(:email_addresses, vals.reject(&:blank?))
  end
end

Gemfile

ruby '2.2.0'
source 'https://rubygems.org'

...

gem 'font-awesome-rails'

sample_migration.rb

class AddEmailAddressesToClients < ActiveRecord::Migration
  def change
    add_column :clients, :email_addresses, :text, array: true, default: []
    add_index :clients, :email_addresses, using: 'gin'
  end
 
end

Updated to use the choices wrapping

Added model note for removing blank entries (with AA 1.1 and mongoid, blank entries are added to the Array field on the document)