Скачать или смотреть Mastering not-contains Queries in ElasticSearch

Learn how to construct effective `not-contains` queries in ElasticSearch using Boolean queries. This post provides examples and Java code for seamless integration.
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Mastering not-contains Queries in ElasticSearch: A Comprehensive Guide

When working with ElasticSearch in a Java application, you might often need to filter out specific entries from your data based on certain criteria. One common requirement is the need to execute a not-contains query. For instance, if you are dealing with a category field and looking to exclude any entries that contain the substring "fast", this guide will guide you through building such a query step-by-step.

Understanding the Problem

Imagine you have a dataset with different categories such as:

Car

Bus

Train

Fastcar

You need to formulate a query to retrieve all entries without the substring "fast" in their category. This can be a bit tricky if you are new to ElasticSearch, especially if the previous attempts you've made didn't yield the expected results. But don't worry! Below, we will walk you through the solution.

Crafting the not-contains Query

To successfully exclude entries containing a certain substring, you can leverage ElasticSearch's powerful Boolean queries. The must_not clause allows you to specify conditions that must not be met. Below is an example of how to build such a query:

ElasticSearch Query Example

Here’s how the query would look in Kibana:

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

Breakdown of the Query Components

GET my_index/_search: Specifies the index you are querying.

bool: A query that matches documents matching a boolean combination of other queries.

must_not: The conditions that must not be true for a document to be included in the results.

wildcard query: The operator used for matching substrings, with * denoting any characters after "fast".

Implementing in Java

Now, let’s see how to translate this query into Java code using the ElasticSearch client:

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

Explanation of the Code

SearchSourceBuilder: This builds the search request, containing the query logic.

mustNot clause: This encapsulates our not-contains logic using the wildcardQuery for matching.

SearchRequest: Represents the search action in the context of the specified index.

restHighLevelClient: The ElasticSearch client object used to communicate with the ElasticSearch server and execute the search.

Common Issues and Tips

If your results still include unwanted entries (such as those labeled "Aufzugsstoerung"), consider the following tips:

Double-check your index: Ensure that the index name and field you are querying actually match the data structure in ElasticSearch.

Query context: The placement of your must_not clause can affect the output. Confirm that it targets the right level in the query.

Use wildcard filters: Always utilize wildcards correctly to match all relevant variations of strings.

Conclusion

Building a not-contains query in ElasticSearch requires understanding how to use Boolean logic effectively. By following the examples provided, you can successfully filter out entries that you do not wish to include in your search results. Now, anytime you need to craft similar queries, refer back to this guide to streamline your ElasticSearch operations.

Happy coding!