4.3. Using an ISO Formatted Date for Document IDs

The ISO 8601 date standard describes a useful scheme for representing a date string in a Year-Month-DayTHour:Minute:Second.microsecond format. For time-bound documents in a CouchDB database this can be a very handy way to create a unique identifier, since JavaScript can directly use it to create a Date object. Using this sample map function:

  1. function(doc) {
  2.   var dt = new Date(doc._id);
  3.   emit([dt.getDate(), doc.widget], 1);
  4. }

simply use group_level to zoom in on whatever time you wish to use.

  1. curl -X GET "http://localhost:5984/transactions/_design/widget_count/_view/toss?group_level=1"
  3. {"rows":[
  4. {"key":[20],"value":10},
  5. {"key":[21],"value":20}
  6. ]}
  8. curl -X GET "http://localhost:5984/transactions/_design/widget_count/_view/toss?group_level=2"
  10. {"rows":[
  11. {"key":[20,widget],"value":10},
  12. {"key":[21,widget],"value":10},
  13. {"key":[21,thing],"value":10}
  14. ]}

Another method is using parseint() and datetime.substr() to cut out useful values for a return key:

  1. function (doc) {
  2.   var datetime = doc._id;
  3.   var year = parseInt(datetime.substr(0, 4));
  4.   var month = parseInt(datetime.substr(5, 2), 10);
  5.   var day = parseInt(datetime.substr(8, 2), 10);
  6.   var hour = parseInt(datetime.substr(11, 2), 10);
  7.   var minute = parseInt(datetime.substr(14, 2), 10);
  8.   emit([doc.widget, year, month, day, hour, minute], 1);
  9. }