app/models/effective/datatable_column_tool.rb
def size(collection)
      count = (collection.size rescue nil)

      case count
      when Integer
        count
      when Hash
        count.size  # This represents the number of displayed datatable rows, not the sum all groups (which might be more)
      else
        if collection.klass.connection.respond_to?(:unprepared_statement)
          collection_sql = collection.klass.connection.unprepared_statement { collection.to_sql }
          (collection.klass.connection.exec_query("SELECT COUNT(*) FROM (#{collection_sql}) AS datatables_total_count").rows[0][0] rescue 1)
        else
          (collection.klass.connection.exec_query("SELECT COUNT(*) FROM (#{collection.to_sql}) AS datatables_total_count").rows[0][0] rescue 1)
        end.to_i
      end
    end
def size(collection)
      count = (collection.size rescue nil)

      case count
      when Integer
        count
      when Hash
        count.size  # This represents the number of displayed datatable rows, not the sum all groups (which might be more)
      else
        if collection.klass.connection.respond_to?(:unprepared_statement)
          collection_sql = collection.klass.connection.unprepared_statement { collection.to_sql }
          (collection.klass.connection.exec_query("SELECT COUNT(*) FROM (#{collection_sql}) AS datatables_total_count").rows[0][0] rescue 1)
        else
          (collection.klass.connection.exec_query("SELECT COUNT(*) FROM (#{collection.to_sql}) AS datatables_total_count").rows[0][0] rescue 1)
        end.to_i
      end
    end
Not every ActiveRecord query will work when calling the simple .count
 Custom selects:
   User.select(:email, :first_name).count will throw an error
 Grouped Queries:
   User.all.group(:email).count will return a Hash