Update API: Add support for scripted upserts.

[markharwood]

In the case of inserts the UpdateHelper class will now allow the script used to apply updates to run on the upsert doc provided by clients. This allows the logic for managing the internal state of the data item to be managed by the script and is not reliant on clients performing the initialisation of data structures managed by the script.
Associated issue: #7143

[martijnvg]

Maybe these if statements can be combined? Something like this:

if (!"create".equals(scriptOpChoice)) {
   if ("none".equals(scriptOpChoice)) {
      logger.warn("Used upsert operation [{}] for script [{}], doing nothing...", scriptOpChoice, request.script);
   }
   UpdateResponse update = new UpdateResponse(getResult.getIndex(), getResult.getType(), getResult.getId(),
   getResult.getVersion(), false);
   update.setGetResult(getResult);
   return new Result(update, Operation.NONE, upsertDoc, XContentType.JSON);
}

[markharwood]

Thanks, Martijn. Looks good but the log msg should only be output if not none i.e.

if (!"none".equals(scriptOpChoice)) {
    logger.warn("Used upsert operation [{}] for script [{}], doing nothing...", scriptOpChoice, request.script);
}

[martijnvg]

@markharwood LGTM

[jpountz]

use underscore_case for consistency with the rest of the docs?

[markharwood]

Will go ahead and push if no objections

[jpountz]

LGTM

[markharwood]

Committed in e6b459c

[dadoonet]

This should return this;