Elasticsearch JS - Variable [x] is not defined

Question

In a test Elasticsearch index, I have indexed a document, and I now want to update the document by setting its length property to 100. I want to do this through scripting (as this is a simplified example to illustrate my problem) via the elasticsearch package.

client.update({
  index: 'test',
  type: 'object',
  id: '1',
  body: {
    script: 'ctx._source.length = length',
    params: { length: 100 }
  }
})

However, I receive the following error:

{
  "error": {
    "root_cause": [
      {
        "type": "remote_transport_exception",
        "reason": "[6pAE96Q][127.0.0.1:9300][indices:data/write/update[s]]"
      }
    ],
    "type": "illegal_argument_exception",
    "reason": "failed to execute script",
    "caused_by": {
      "type": "script_exception",
      "reason": "compile error",
      "script_stack": [
        "ctx._source.length = length",
        "                     ^---- HERE"
      ],
      "script": "ctx._source.length = length",
      "lang": "painless",
      "caused_by": {
        "type": "illegal_argument_exception",
        "reason": "Variable [length]is not defined."
      }
    }
  },
  "status": 400
}

This happens even though I have included the length property in body.params.length.

Using the following:

• Elasticsearch server v6.1.1
• Elasticsearch JavaScript client v14.1.0

How can I resolve this issue?

Answer 1

The documentation is wrong at https://www.elastic.co/guide/en/elasticsearch/client/javascript-api/current/api-reference.html#api-update

In their example, they put:

client.update({
  index: 'myindex',
  type: 'mytype',
  id: '1',
  body: {
    script: 'ctx._source.tags += tag',
    params: { tag: 'some new tag' }
  }
}, function (error, response) {
  // ...
});

Whilst in fact, body.script should read:

client.update({
  index: 'myindex',
  type: 'mytype',
  id: '1',
  body: {
    script: {
      lang: 'painless',
      source: 'ctx._source.tags += params.tag',
      params: { tag: 'some new tag' }
    }
  }
}, function (error, response) {
  // ...
});

Therefore, if you change your script to:

script: {
  lang: 'painless',
  source: 'ctx._source.length = params.length',
  params: { length: 100 }
}

it should work!

---

You may want to reference the Painless Examples - Updating Fields with Painless page!