Скачать или смотреть Mastering Jolt: Dynamically Access JSON Values in Apache NiFi

Learn how to effectively use Jolt in Apache NiFi to dynamically reference JSON values. This guide will help you create complex JSON structures for your data processing needs.
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This video is based on the question https://stackoverflow.com/q/67888557/ asked by the user 'ThisIsMe' ( https://stackoverflow.com/u/8215457/ ) and on the answer https://stackoverflow.com/a/67890409/ provided by the user 'Barbaros Özhan' ( https://stackoverflow.com/u/5841306/ ) at 'Stack Overflow' website. Thanks to these great users and Stackexchange community for their contributions.

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Mastering Jolt: Dynamically Access JSON Values in Apache NiFi

If you're working with JSON data in Apache NiFi, you may have encountered the need to transform and manipulate JSON arrays dynamically. Specifically, you might struggle with how to create references to object values in JSON using Jolt while avoiding common pitfalls. In this post, we'll address a scenario where you need to reference dynamic JSON keys and provide a clear solution to help you achieve the desired output.

The Problem

Let's look at a practical example. Suppose you have a JSON object that contains some metadata and an array of keys, like this:

[[See Video to Reveal this Text or Code Snippet]]

Your goal is to transform this JSON object into a new structure where each item in the listitems array becomes an object in a new processlist array. The output should resemble the following:

[[See Video to Reveal this Text or Code Snippet]]

However, you may encounter issues when trying to reference the values using @ () syntax. Let's break down the solution into manageable steps.

The Jolt Solution

Step 1: Understanding the Shift Operation

In Jolt, the shift operation is commonly used to transform the structure of JSON data. The challenge lies in dynamically accessing the values based on an array of keys.

Step 2: Using the * Key

To achieve your desired output, you can add an additional level to nest the current spec while iterating through the listitems. By incorporating (3,&) along with the * key, you can directly reference the current keys:

Here's how you can structure your Jolt specification:

[[See Video to Reveal this Text or Code Snippet]]

Step 3: Explanation of the Specification

Nested * Keys: Adding an extra * allows you to loop through each item dynamically.

@ 1 Reference: @ 1 retrieves the current value in your listitems array (e.g., name or id), which you use to populate type.

Dynamic Key Access with @ (3,&): This is the key part that lets you access the parent values dynamically based on what is defined in listitems. The & symbol stands for the current key being processed (name or id).

Conclusion

By leveraging this Jolt specification, you can effectively transform JSON arrays into the desired structure for your data processing needs in Apache NiFi. This approach not only provides a clean solution to the problem but also enhances your understanding of how to manipulate JSON using Jolt.

If you're handling JSON in an Apache NiFi workflow, understanding how to dynamically reference values can significantly improve your data processing capabilities. Happy coding!