Issue with date format change while reindexing

Elastic Stack Elasticsearch
11

Here is a way to do it:

POST _ingest/pipeline/_simulate
{
  "pipeline" :{
  "description": "date pipeline ",
  "processors": [
    {
        "script": {
          "source": """
             SimpleDateFormat format = new SimpleDateFormat("yyyy-MM-dd");
             ctx.person.birthDate = format.format(format.parse(ctx.person.birthDate));
          """
        }
    }
  ]},
  "docs": [
    {
      "_index": "index",
      "_type": "_doc",
      "_id": "id",
       "_source": {
          "person": {
            "birthDate": "1950-01-01T12:00:00.000Z"
          }
       }
    }
  ]
}

This gives:

{
  "docs" : [
    {
      "doc" : {
        "_index" : "index",
        "_type" : "_doc",
        "_id" : "id",
        "_source" : {
          "person" : {
            "birthDate" : "1950-01-01"
          }
        },
        "_ingest" : {
          "timestamp" : "2019-02-26T17:35:45.52603Z"
        }
      }
    }
  ]
}

HTH