ActiveAdmin + reorder index table using jQuery.sortable

admin__categories.rb

ActiveAdmin.register Category do

  index do
    reorderable_column(self)
    column :name
  end
  
  controller do
    private

    def reorderable_column(dsl)
      dsl.column('Reorder', sortable: false) do
        dsl.fa_icon :arrows, class: "js-reorder-handle"
      end
    end

    helper_method :reorderable_column
  end

  collection_action :reorder, method: :patch do
    positions = params.require(:positions)
    # TODO: add validation e.g. require each position is uniq: positions.values.uniq.size == positions.size 
    # TODO: do not allow reordering if Filtering, Pagination or Sorting is applied.
    resource_class.transaction do
      positions.each do |id, position|
        item = resource_class.find_by(id: id)
        new_position = position.to_i + 1
        item.update_column(:position, new_position) if item.position != new_position
      end
    end

    render json: { status: "success" }
  end
end

adtive_admin__views__components__table_for_data.rb

module ActiveAdmin
  module Views
    # Adds data-id attribute to the <tr> tag rendering ActiveAdmin index tables
    module TableForData

      def build_table_body
        @tbody = tbody do
          # Build enough rows for our collection
          @collection.each do |elem|
            classes = [cycle('odd', 'even')]

            if @row_class
              classes << @row_class.call(elem)
            end

            tr(class: classes.flatten.join(' '), id: dom_id_for(elem), 'data-id': id_for(elem))
          end
        end
      end

      private

      def id_for(record)
        record.id if record.respond_to?(:id)
      end
    end
  end
end

ActiveAdmin::Views::TableFor.prepend ActiveAdmin::Views::TableForData

assets__javascripts__admin__sortable_index.js

$(document).ready(function () {
    $(".sortable tbody").sortable({
        update: function () {
            $.ajax({
                url: "/admin/categories/reorder",
                type: 'patch',
                data: serializePositions(this),
                complete: function () {
                }
            });
        }
    });

    var serializePositions = function (items_container) {
        var result = {};
        $.each($(items_container).find('tr'), function (i, elem) {
            result[$(elem).data('id')] = i;
        });
        return {positions: result};
    };
});

db__migrate__add_positions.rb

class AddPosition < ActiveRecord::Migration
  MODELS = [Category, Model2, Model3]
  def up
    MODELS.each do |model|
      add_column model.table_name, :position, :integer, index: true

      model.all.each_with_index { |item, index| item.update_column(:position, index + 1) }
    end
  end

  def down
    MODELS.each do |model|
      remove_column model.table_name, :position
    end
  end
end

Example implies:
You are using ActiveAdmin, models with a few (dozen) of records max, no Paging, Filtering or Ordering is applied.

Note:
URL "/admin/categories/reorder" could also be parameterized, then the whole approach could take defaults, with a single required configuration setting: reorderable_models = [Categoy, Model2, Model3] .