Shorten your script

Using syntactic abilities that are native to Painless, you can reduce verbosity in your scripts and make them shorter. Here’s a simple script that we can make shorter:

GET my-index-000001/_search
{
  "script_fields": {
    "my_doubled_field": {
      "script": {
        "lang":   "painless",
        "source": "return doc['my_field'].value * params.get('multiplier');",
        "params": {
          "multiplier": 2
        }
      }
    }
  }
}

Let’s look at a shortened version of the script to see what improvements it includes over the previous iteration:

GET my-index-000001/_search
{
  "script_fields": {
    "my_doubled_field": {
      "script": {
        "source": "field('my_field').get(null) * params['multiplier']",
        "params": {
          "multiplier": 2
        }
      }
    }
  }
}

This version of the script removes several components and simplifies the syntax significantly:

• The lang declaration. Because Painless is the default language, you don’t need to specify the language if you’re writing a Painless script.
• The return keyword. Painless automatically uses the final statement in a script (when possible) to produce a return value in a script context that requires one.
• The get method, which is replaced with brackets []. Painless uses a shortcut specifically for the Map type that allows us to use brackets instead of the lengthier get method.
• The semicolon at the end of the source statement. Painless does not require semicolons for the final statement of a block. However, it does require them in other cases to remove ambiguity.

You can use this abbreviated syntax anywhere that Elasticsearch supports scripts, such as when you’re creating runtime fields. Be mindful, however, that the field access API is not a direct replacement for doc. This shortened version of the original script includes a default value (the null), so depending on the field type the script may access either doc values or _source. Some fields will use _source as a fallback if doc values aren't available for a specific field.