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Learn how to effectively use ElasticSearch to return only the specific parts of your JSON documents, optimizing your queries with nested mappings and inner hits.
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How to Retrieve Specific Parts of Your ElasticSearch Documents

ElasticSearch is a powerful search engine that allows you to index and search through large volumes of documents quickly. However, sometimes you need more control over the results you receive, especially when you are dealing with complex structures like JSON. This blog will guide you through the process of retrieving only specific parts of your ElasticSearch documents.

The Problem

Let's say you have a JSON document with a structure similar to this:

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

When performing a search using a query like mydata.Key4:"line one", ElasticSearch returns the entire document, but you only want to retrieve the first matching part of the JSON, specifically:

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

The central question here is: How can you modify your queries so that you retrieve only this specific information?

The Solution

The issue arises mainly from how your data is indexed and how ElasticSearch’s mapping works. Let’s break down the solution:

1. Define Proper Mapping

To start, ensure that your data has the correct mapping. When you don’t define mappings, the fields will be treated as individual properties of type text (not nested). You should set your mapping to use nested types so that you can leverage ElasticSearch’s inner hits feature.

Here’s how you can define the mapping for your data:

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

2. Re-index Your Documents

After updating the mapping, re-index your documents. This makes sure that the new structure is applied properly to your existing data.

3. Use Nested Queries

Once your documents are indexed correctly, you can conduct a nested query. Here’s a sample query:

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

4. Advantages of Using term Query

It's important to note that when you use the match query, ElasticSearch tokenizes your search term. For example, line one would be split into the tokens line and one. This can cause unexpected results, such as also including line two in your results.

A term query, on the other hand, does not analyze the input and looks for an exact match. Therefore, it’s the right choice when you want to ensure the precision of your results.

Conclusion

By following these steps, you should be able to retrieve only the specific parts of your JSON documents that match your query. Setting up the correct mapping and understanding how to leverage nested queries and term searches enables you to optimize your ElasticSearch experience effectively.

If you still face issues or have further queries, feel free to ask! Happy searching!