Скачать или смотреть How to Read JSON Fields Dynamically in Kusto Queries: Accessing Values by Key Name

Learn how to effectively handle and read dynamic JSON fields in Kusto queries, ensuring that you can access values like PolicyId robustly, regardless of their order.
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How to Read JSON Fields Dynamically in Kusto Queries: Accessing Values by Key Name

When working with JSON data in Kusto Query Language (KQL), accessing specific fields can be tricky, particularly when the order of fields and their presence is not guaranteed. If you've ever found yourself frustrated trying to parse dynamic JSON fields, you're not alone! Let's dive into a common scenario and explore a robust solution.

The Problem: Accessing JSON Fields

Imagine you have JSON data resulting from a query similar to this:

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

The output might look something like this:

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

Your goal is to extract a field like PolicyId using the following query:

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

However, this approach has a major flaw: it relies on the position of the item in the array (e.g., [1]), which can lead to errors if the array order changes or if fields are missing altogether.

The Solution: Access JSON Fields by Key Name

To bypass the pitfalls of positional references, we can refine our approach to access JSON fields directly by key name. Here’s how you can do it effectively:

Step 1: Create a Sample Dataset

We'll start by defining a sample dataset that mimics the structure of our JSON data:

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

Step 2: Use mv-apply to Extract Values

Next, apply the mv-apply operator to work through the JSON entries dynamically while checking for specific key values. Here’s how you can do it:

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

Step 3: Analyze Your Results

The output will be neatly summarized, showing the extracted IP and PolicyId values:

IPPolicyIde000::5890, 128.1.1.1PC100921Conclusion

By using mv-apply and key-value checks, you can flexibly and reliably extract dynamic JSON fields, making your Kusto queries much more robust and user-friendly. This method avoids the pitfalls of relying on positional indexing and instead focuses directly on the keys that you're interested in, ensuring that you can access the desired fields no matter how they're arranged in the JSON.

In summary, shift your focus from indices to keys to strengthen your data queries. Whether you're a seasoned Kusto user or just starting, leveraging dynamic JSON fields effectively can significantly enhance your data manipulation capabilities.