Convert date to year-month-day format with Painless

Question

I have dates in this format: 2018-07-24T08:27:59.259Z. What is the best way to convert this to 2018-07-24 in Painless? Looking through the Painless API reference, I realise there are methods such as getYear(), getMonth() and getDayOfMonth(), but I was wondering if there is a simpler way.

Answer 1

An easy way to achieve this without having to mess up with dates is to simply split on the T character, like this:

POST test/_update_by_query
{
  "script": {
    "source": "ctx._source.date = /T/.split(ctx._source.date)[0]"
  }
}