if operator == "="
      "( #{TimeBooking.table_name}.project_id IN (" + value.collect { |val| "'#{connection.quote_string(val)}'" }.join(",") + ") )"
    else
      "( #{TimeBooking.table_name}.project_id NOT IN (" + value.collect { |val| "'#{connection.quote_string(val)}'" }.join(",") + ") OR #{TimeBooking.table_name}.project_id IS NULL )"