Elasticsearch Mastering Painless Scripting Language in Elasticsearch

By Opster Team

Updated: Nov 5, 2023

| 2 min read

Overview

This article will delve into the advanced aspects of Painless and how to use it effectively in Elasticsearch.

Painless is a statically-typed language, which means that the type of each variable and expression is known at compile-time. This feature allows Painless to provide safety guarantees and also to generate efficient bytecode. It supports a syntax similar to Groovy and JavaScript, making it familiar and easy to learn for users with a background in those languages.

One of the key features of Painless is its strong typing system. This means that every variable and expression has a known type at compile time, which allows for efficient bytecode generation and safety guarantees. Painless supports a variety of types, including primitives like int and boolean, as well as complex types like arrays and maps.

Usage & Examples

Let’s look at an example of a Painless script:

java
POST /_scripts/calculate-score
{
  "script": {
    "lang": "painless",
    "source": "Math.log(_score * 2) + params.my_modifier"
  }
}

In this script, `_score` is a predefined variable that represents the score of the current document, and `my_modifier` is a parameter that can be passed to the script when it is executed. The script calculates a new score for each document based on these inputs.

Painless also provides a rich set of operators and functions for manipulating data. For example, it supports all the standard arithmetic operators (`+`, `-`, `*`, `/`, `%`), comparison operators (`<`, `>`, `<=`, `>=`, `==`, `!=`), and logical operators (`&&`, `||`, `!`). It also provides functions for common tasks like string manipulation, regular expression matching, and date/time manipulation.

Here is an example of using some of these operators and functions in a Painless script:

java
POST /_scripts/calculate-age
{
  "script": {
    "lang": "painless",
    "source": "Instant.ofEpochMilli(doc['birth_date'].value.millis).atZone(ZoneId.of('Z')).toLocalDate().until(LocalDate.now(), ChronoUnit.YEARS)"
  }
}

In this script, `doc[‘birth_date’].value.millis` retrieves the birth date of the current document as a timestamp in milliseconds, and the rest of the script calculates the age in years from this timestamp until now.

Painless also supports control flow statements like `if`, `else`, `while`, `for`, and `do`. These can be used to implement complex logic in your scripts. For example, you could use a `for` loop to iterate over an array field in a document and calculate a sum or average.

java
POST /_scripts/calculate-average
{
  "script": {
    "lang": "painless",
    "source": "double sum = 0; for (int i = 0; i < doc['values'].length; i++) { sum += doc['values'][i]; } return sum / doc['values'].length;"
  }
}

In this script, `doc[‘values’]` retrieves the `values` field of the current document as an array, and the `for` loop calculates the average of these values.

Conclusion

In conclusion, Painless is a powerful and flexible scripting language that can be used to implement complex logic in Elasticsearch. By understanding its features and syntax, you can write efficient and safe scripts for your Elasticsearch applications.