Book Image

Elasticsearch Essentials

By : Bharvi Dixit
Book Image

Elasticsearch Essentials

By: Bharvi Dixit

Overview of this book

With constantly evolving and growing datasets, organizations have the need to find actionable insights for their business. ElasticSearch, which is the world's most advanced search and analytics engine, brings the ability to make massive amounts of data usable in a matter of milliseconds. It not only gives you the power to build blazing fast search solutions over a massive amount of data, but can also serve as a NoSQL data store. This guide will take you on a tour to become a competent developer quickly with a solid knowledge level and understanding of the ElasticSearch core concepts. Starting from the beginning, this book will cover these core concepts, setting up ElasticSearch and various plugins, working with analyzers, and creating mappings. This book provides complete coverage of working with ElasticSearch using Python and performing CRUD operations and aggregation-based analytics, handling document relationships in the NoSQL world, working with geospatial data, and taking data backups. Finally, we’ll show you how to set up and scale ElasticSearch clusters in production environments as well as providing some best practices.
Table of Contents (12 chapters)
11
Index

Elasticsearch Query-DSL

Query-DSL is a JSON interface provided by Elasticsearch to write queries in the JSON format. It allows you to write any query that you may write in Lucene. The queries can be as simple as just matching simple terms, or they can be very complex.

Until now, to retrieve documents from Elasticsearch we used a GET request that was dependent on the ID to search and retrieve the document. You can extend the searches in similar way; for example: localhost:9200/index_name/doc_type/_search?q=category:databases.

The preceding query is a typical Lucene query string that searches for the databases word inside the category field. Submitting queries to Elasticsearch in this way is very limited, so you will learn about Query-DSL now.

Syntax:

The Query-DSL follows the following syntax:

{
  "query": {},
  "from": 0,
  "size": 20,
  "_source": ["field1","field2"]
}