custom-sidebar-filters-for-active-admin-ex5.rb

# app/models/my_model.rb
def self.ransackable_scopes(_auth_object = nil)
  %i[activated_in_period_gteq_datetime activated_in_period_lteq_datetime]
end

def self.activated_in_period_gteq_datetime(date_from)
  joins(:user).where('users.activation_date >= ?', date_from)
end

def self.activated_in_period_lteq_datetime(date_to)
  joins(:user).where('users.activation_date <= ?', date_from)
end