Use with https://github.com/ebeigarts/mongoid_active_admin_app/blob/master/config/initializers/active_admin_mongoid_patches.rb to enable Mongoid support in ActiveAdmin.

active_admin_mongoid_patch.rb

# config/initializers/active_admin_mongoid_patch.rb

require "active_admin"
require "active_admin/resource_controller"
require 'ostruct'

module ActiveAdmin
  class Namespace
    # Disable comments
    def comments?
      false
    end
  end

  class Resource
    def resource_table_name
      controller.resources_configuration[:self][:route_instance_name]
    end

    # Disable filters
    def add_default_sidebar_sections
    end
  end

  class ResourceController
    # Use #desc and #asc for sorting.
    def sort_order(chain)
      params[:order] ||= active_admin_config.sort_order
      table_name = active_admin_config.resource_table_name
      if params[:order] && params[:order] =~ /^([\w\_\.]+)_(desc|asc)$/
        chain.send($2, $1)
      else
        chain # just return the chain
      end
    end

    # Disable filters
    def search(chain)
      chain
    end
  end

  # Fix for following commit which added the ActiveRecord-only 'reorder' method:
  # https://github.com/gregbell/active_admin/commit/bf341ba505e76ac6ab8d083ffb0b821e6d8ae1f8#lib/active_admin/views/pages/index.rb
  module Views
    module Pages
      class Index
        protected
        def items_in_collection?
          collection.limit(1).exists?
        end
      end
    end
  end

  module Mongoid
    COLUMN_TYPES = { Bignum => :integer, Array => :string }

    module Patches
      def self.included(base)
        raise 'Include ActiveAdmin::Mongoid::Patches after Mongoid::Document' unless base.respond_to?(:collection_name)
        base.extend ClassPatches
      end

      def column_for_attribute(attr)
        self.class.columns.detect { |c| c.name == attr.to_s }
      end

      module ClassPatches
        HIDDEN_COLUMNS = %w(_id _type)

        def content_columns
          fields.map do |name, field|
            next if HIDDEN_COLUMNS.include?(name)
            OpenStruct.new.tap do |c|
              c.name = field.name
              c.type = ActiveAdmin::Mongoid::COLUMN_TYPES[field.type] || field.type.to_s.downcase.to_sym
            end
          end.compact
        end

        def columns
          content_columns
        end
      end
    end
  end
end

company.rb

# app/models/company.rb

class Company
  include Mongoid::Document
  include ActiveAdmin::Mongoid::Patches

  field ...
end

Thanks for this great fix!

Really nice!
BTW https://github.com/elia/activeadmin-mongoid/