# Reindex API - Reference doc **URL:** \ **Category:** Elasticsearch\ **Created:** [October 8, 2017, 6:55am UTC](https://discuss.elastic.co/t/reindex-api-reference-doc/103140 "2017-10-08T06:55:13Z")\ **Posts on this page:** 12\ **Page:** 1
**Author:** ![shaharmor](https://avatars.discourse-cdn.com/v4/letter/s/58f4c7/32.png) [@shaharmor](https://discuss.elastic.co/u/shaharmor)\ **Post date:** [October 8, 2017, 6:55am UTC](https://discuss.elastic.co/t/reindex-api-reference-doc/103140/1 "2017-10-08T06:55:13Z")
Hi, I'm trying to use the Reindex API to update an existing document, but I can't seem to find how to increment the value of the existing field with the value of the new document. ---
**Author:** ![dadoonet](https://sea2.discourse-cdn.com/elastic/user_avatar/discuss.elastic.co/dadoonet/32/137187_2.png) [@dadoonet](https://discuss.elastic.co/u/dadoonet)\ **Post date:** [October 8, 2017, 7:25am UTC](https://discuss.elastic.co/t/reindex-api-reference-doc/103140/2 "2017-10-08T07:25:01Z")
I don’t understand. When you reindex, you reindex an old document. What do you mean by referencing the value of a new document? ---
**Author:** ![shaharmor](https://avatars.discourse-cdn.com/v4/letter/s/58f4c7/32.png) [@shaharmor](https://discuss.elastic.co/u/shaharmor)\ **Post date:** [October 8, 2017, 7:31am UTC](https://discuss.elastic.co/t/reindex-api-reference-doc/103140/3 "2017-10-08T07:31:15Z")
Forget it. I though you can also update the existing doc when using the Reindex API, but apparently you can't. ---
**Author:** ![dadoonet](https://sea2.discourse-cdn.com/elastic/user_avatar/discuss.elastic.co/dadoonet/32/137187_2.png) [@dadoonet](https://discuss.elastic.co/u/dadoonet)\ **Post date:** [October 8, 2017, 8:05am UTC](https://discuss.elastic.co/t/reindex-api-reference-doc/103140/4 "2017-10-08T08:05:58Z")
But you can. You can add an ingest pipeline with a painless script which edits the old document before reindexing it. ---
**Author:** ![shaharmor](https://avatars.discourse-cdn.com/v4/letter/s/58f4c7/32.png) [@shaharmor](https://discuss.elastic.co/u/shaharmor)\ **Post date:** [October 8, 2017, 8:09am UTC](https://discuss.elastic.co/t/reindex-api-reference-doc/103140/5 "2017-10-08T08:09:33Z")
Hmm thats a really good point. Can i also use that for upserting when the doc doesn't exist? ---
**Author:** ![shaharmor](https://avatars.discourse-cdn.com/v4/letter/s/58f4c7/32.png) [@shaharmor](https://discuss.elastic.co/u/shaharmor)\ **Post date:** [October 8, 2017, 8:16am UTC](https://discuss.elastic.co/t/reindex-api-reference-doc/103140/6 "2017-10-08T08:16:50Z")
I don't see where in the docs of the script processor I can access both the existing doc and the new doc ---
**Author:** ![shaharmor](https://avatars.discourse-cdn.com/v4/letter/s/58f4c7/32.png) [@shaharmor](https://discuss.elastic.co/u/shaharmor)\ **Post date:** [October 8, 2017, 8:52am UTC](https://discuss.elastic.co/t/reindex-api-reference-doc/103140/7 "2017-10-08T08:52:52Z")
I'm actually pretty sure you can't do it, as the ingestion phase can be located to different nodes which don't hold the data. ---
**Author:** ![dadoonet](https://sea2.discourse-cdn.com/elastic/user_avatar/discuss.elastic.co/dadoonet/32/137187_2.png) [@dadoonet](https://discuss.elastic.co/u/dadoonet)\ **Post date:** [October 8, 2017, 9:32am UTC](https://discuss.elastic.co/t/reindex-api-reference-doc/103140/8 "2017-10-08T09:32:14Z")
> [@shaharmor](#): > > Can i also use that for upserting when the doc doesn't exist? That’s confusing. Reindex API is reindexing documents from an existing index. So the document exists for sure. ---
**Author:** ![dadoonet](https://sea2.discourse-cdn.com/elastic/user_avatar/discuss.elastic.co/dadoonet/32/137187_2.png) [@dadoonet](https://discuss.elastic.co/u/dadoonet)\ **Post date:** [October 8, 2017, 9:33am UTC](https://discuss.elastic.co/t/reindex-api-reference-doc/103140/9 "2017-10-08T09:33:17Z")
The “new” doc is the existing doc. I think you are not understanding what reindex api is. ---
**Author:** ![shaharmor](https://avatars.discourse-cdn.com/v4/letter/s/58f4c7/32.png) [@shaharmor](https://discuss.elastic.co/u/shaharmor)\ **Post date:** [October 8, 2017, 9:37am UTC](https://discuss.elastic.co/t/reindex-api-reference-doc/103140/10 "2017-10-08T09:37:06Z")
I understand. Its "re-indexing" existing documents from 1 index to another. But there can be a situation where you have 3 documents: Given you are re-indexing from index1 to index2: 1. the original document in index1 2. an existing document in index2 3. the re-indexed document that is being copied from index1 to index2 If I set the `ctx._id` of the soon-to-be-reindexed document to the same as an existing one, it will override the older doc with this new one. My question is, can I use the same Reindex API to **update** the old document instead of overriding it? ---
**Author:** ![dadoonet](https://sea2.discourse-cdn.com/elastic/user_avatar/discuss.elastic.co/dadoonet/32/137187_2.png) [@dadoonet](https://discuss.elastic.co/u/dadoonet)\ **Post date:** [October 8, 2017, 10:22am UTC](https://discuss.elastic.co/t/reindex-api-reference-doc/103140/11 "2017-10-08T10:22:46Z")
I see. No it will override. But if you have a document ``` { “foo”: “bar” } ``` And reindex it, it will become: ``` { “foo”: “bar” } ``` You can apply an ingest script if you wish so you document can become: ``` { “foo”: “barbaz”, “age”: 20 } ``` If you wish ---
**Author:** ![system](https://us1.discourse-cdn.com/elastic/original/3X/1/a/1ac57faf039f6b580b3f104ef42a2a89e41014de.png) [@system](https://discuss.elastic.co/u/system)\ **Post date:** [November 5, 2017, 10:22am UTC](https://discuss.elastic.co/t/reindex-api-reference-doc/103140/12 "2017-11-05T10:22:59Z")
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