# Efficient date difference at document upsert
**URL:** https://discuss.elastic.co/t/efficient-date-difference-at-document-upsert/119823
**Category:** Elasticsearch
**Created:** [February 14, 2018, 3:04pm UTC](https://discuss.elastic.co/t/efficient-date-difference-at-document-upsert/119823 "2018-02-14T15:04:24Z")
**Posts on this page:** 3
**Page:** 1
### Author:  [@DidierB](https://discuss.elastic.co/u/DidierB)
#### Post date: [February 14, 2018, 3:04pm UTC](https://discuss.elastic.co/t/efficient-date-difference-at-document-upsert/119823/1 "2018-02-14T15:04:24Z")
Hello,
I would like to make thousands of upsert and computing a time difference between the document already indexed (not with a time-based key but with an id key) and an already stored date, so I can tell what was the last time between two connections.
I would like to do something like this in my script:
`ctx._source.diffdate = params.infodate.epoch_second - ctx._source.lastinfodate.epoch_second`
Where params.infodate contains the latest timestamp and the ctx.\_source. **lastinfodate** contains the former latest timestamp.
**In the mapping, the lastinfodate is known as a Date but, in the script, it is known as a String** , so I can't access epoch\_second method.
`"reason" : "Unable to find dynamic field [epoch_second] for class [java.lang.String]."`
I would like to load the field directly as a number in the script to do the difference. Doing "string to date" conversion in the script would result in an non-affordable CPU time.
How can I do it?
---
### Author:  [@DidierB](https://discuss.elastic.co/u/DidierB)
#### Post date: [February 15, 2018, 1:47pm UTC](https://discuss.elastic.co/t/efficient-date-difference-at-document-upsert/119823/2 "2018-02-15T13:47:22Z")
Well, at the injection I used a timestamp conversion in integer so I do arithmetics.
---
### Author:  [@system](https://discuss.elastic.co/u/system)
#### Post date: [March 15, 2018, 1:47pm UTC](https://discuss.elastic.co/t/efficient-date-difference-at-document-upsert/119823/3 "2018-03-15T13:47:29Z")
This topic was automatically closed 28 days after the last reply. New replies are no longer allowed.