Formtastic PostgreSQL Array input (inspered from https://gist.github.com/franks921/44509c65da3bea99bc49)

active_admin.js

$('form .input.array').each(function() {
  var $wrapper = $('.array-inputs', this);
  var $insertArea = $(".array-input button[data-action=add]").closest(".array-input");
  $(".array-input button[data-action=add]", $(this)).click(function(e) {
    $('.array-input:first-child', $wrapper).clone(true).insertBefore($insertArea).find('input').val('').focus();
  });
  $('.array-input button[data-action=remove]', $wrapper).click(function() {
    if ($('.array-input', $wrapper).length > 2) {
      $(this).parent('.array-input').remove();
    }
  });
});

array_input.rb

class ArrayInput
  include Formtastic::Inputs::Base

  def to_html
    input_wrapping do
      array_wrapping do
        legend_html <<
        array_inputs_wrapping do
          values.each_with_index.map do |value, i|
            array_input_wrapping do
              if value.nil?
                action_button(false)
              else
                array_input_html(value)
              end
            end
          end.join("\n").html_safe
        end
      end
    end
  end

  private

  def values
    values = []

    @object[method].each_with_index do |v, x|
      values << v
    end
    values << "" if values.empty?
    values << nil

    values
  end

  def array_input_html(value)
    button =  action_button
    # template.content_tag(:div) do
      template.text_field_tag("#{object_name}[#{method}][]", value, id: nil) << button
    # end
  end

  def action_button(remove = true)
    if remove
      template.content_tag(:button, template.fa_icon("minus-circle"), type: "button", "data-action": "remove")
    else
      template.content_tag(:button, template.fa_icon("plus-circle"), type: "button", "data-action": "add")
    end
  end

  def array_wrapping(&block)
    template.content_tag(:fieldset,
      template.capture(&block),
      class: "array"
    )
  end

  def array_inputs_wrapping(&block)
    template.content_tag(:ol,
      template.capture(&block),
      class: "array-inputs"
    )
  end

  def array_input_wrapping(&block)
    template.content_tag(:li,
      template.capture(&block),
      class: "array-input"
    )
  end

  def legend_html
    if render_label?
      template.content_tag(:legend,
        template.content_tag(:label, label_text),
        label_html_options.merge(:class => "label")
      )
    else
      "".html_safe
    end
  end
end