How to write an Active Admin custom filter (custom search)

active_admin_custom_filter.rb

ActiveAdmin.register MyModel do
  filter :custom_field, :as => :string, :label => "Custom Field Display Name" 
end

class MyModel < ActiveRecord::Base
  search_methods :custom_field_search
  
  def self.custom_field_search(name)
    # This method should return an ActiveRecord::Relation Object with MyModel objects
    # Put in your complex search logic here
    objects = Model2.where(:user_type => "Student").where('_name like ?', "%#{name}%")
    MyModel.where(:id => objects.map{|u| u.user_id})
  end
end

I guess this was for an older version of active_admin. I don't use it any longer to be able to debug and fix it.