Скачать или смотреть How to Sort Nested Fields in Elasticsearch

Learn how to effectively sort nested fields in Elasticsearch queries. This guide provides a clear explanation along with example code to help you sort nested properties correctly.
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How to Sort Nested Fields in Elasticsearch: A Step-by-Step Guide

When working with Elasticsearch, especially with complex data structures, sorting can sometimes become a bit tricky. One common challenge that developers face involves sorting nested fields. In this guide, we will explore a scenario involving researchers and their affiliations, and how to correctly implement sorting based on nested properties like dateBeginning.

Understanding the Problem

Imagine you have an index called researchers, where each researcher can have multiple affiliations. Each affiliation contains important information such as:

Organisation

Team

Date of beginning

Date of ending

Country

The goal is to sort these affiliations by the dateBeginning field in descending order for a specific researcher identified by their _id.

Given the participant's attempts, it seemed that the initial queries did not yield the desired results. The following query structure was attempted to achieve the sorting:

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

Unfortunately, this query structure did not function as expected. Let’s break down the proper way to implement the sorting.

The Correct Approach to Sorting Nested Fields

Step 1: Understanding Nested Queries

When nesting your queries in Elasticsearch, it is crucial to avoid redundant levels of nesting, particularly when the intention is to sort data. The inner hits do not require an additional nested query; we can simplify the implementation.

Step 2: Simplifying the Query

You can modify the initial query to remove the unnecessary nested querying within the inner_hits portion. Here’s the revised query:

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

This query specifies that you want to retrieve inner hits for the given researcher by matching their _id and sorting the affiliations based on dateBeginning.

Step 3: Sorting at the Top Level

If you wish to sort the top-level results (i.e., the researchers) based on the dateBeginning of their affiliations, here’s how to do that:

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

Key Differences in Syntax

Nested Path: Notice that when sorting at the top level, you use nested_path instead of path. This is essential to ensure Elasticsearch understands that it needs to traverse into the nested structure properly.

Conclusion

Sorting nested fields in Elasticsearch can be straightforward if you understand how to structure your queries correctly. By removing unnecessary nesting and using the correct parameters, you can efficiently retrieve and sort your data based on nested properties like dateBeginning.

With this guide, you can confidently make queries in Elasticsearch that will return results sorted according to your criteria. Happy querying!