Can an ID of an index be not null but empty?

[Java2avaj]

Just a question if by default, an id of an index be empty string value “”? If yes, how to prevent from saving an empty id?

[warkolm (Mark Walkom)]

What do you mean by id of an index exactly?

[Java2avaj]

Thanks for your reply. The “id”/“_id” field. Can we store a document with empty id? If yes, how to prevent it?

[leandrojmp (Leandro Pereira)]

No, the _id can not be empty.

Have you tested it? You can test with the following.

POST test-index/_bulk
{ "index" : { "_index" : "test-index", "_id" : "" } }
{ "field1" : "value1" }

The response will be:

{
  "took": 186,
  "errors": true,
  "items": [
    {
      "index": {
        "_index": "test-index",
        "_id": "",
        "status": 400,
        "error": {
          "type": "illegal_argument_exception",
          "reason": "if _id is specified it must not be empty"
        }
      }
    }
  ]
}