Elasticsearch Displaying Fields in an Elasticsearch Index

By Opster Team

Updated: Jul 23, 2023

| 2 min read

Introduction

In this article, we will discuss how to display fields in an Elasticsearch index. This can be useful for understanding the structure of your data, identifying specific fields, and troubleshooting issues. If you want to learn about Elasticsearch field size – how to calculate the storage size of specific fields in an Index, check out this guide. We will cover the following topics:

1. Using the `_mapping` API to retrieve field information
2. Using the `_search` API to display field values
3. Filtering fields using the `fields` parameter
4. Displaying nested fields

1. Using the `_mapping` API to Retrieve Field Information

The `_mapping` API allows you to retrieve the mapping definition for an index or multiple indices. This includes information about the fields, their data types, and other properties. To retrieve the mapping for a specific index, use the following request:

GET /<index_name>/_mapping

For example, if you have an index named `my_index`, you can retrieve its mapping with the following request:

GET /my_index/_mapping

The response will include the mapping definition for the index, which contains information about the fields and their properties.

It is also possible to retrieve the mapping of one specific field. This can be useful if your mapping is quite big and you only want to focus on a specific field. To retrieve the mapping of a specific field, use the following request:

GET /my_index/_mapping/field/my_field

You can also retrieve the mappings of several fields by separating their names with commas as in the following request:

GET /my_index/_mapping/field/my_field_1,my_field_2,my_field_3

2. Using the `_search` API to Display Field Values

To display the values of fields in an Elasticsearch index, you can use the `_search` API. By default, the `_search` API returns the `_source` field, which contains the original JSON document that was indexed. To display only specific fields, you can use the `_source` parameter in the search request.

Here’s an example of a search request that returns the values of the `title` and `author` fields for documents in the `my_index` index:

GET /my_index/_search
{
  "query": {
    "match_all": {}
  },
  "_source": ["title", "author"]
}

In this example, the `_source` parameter specifies the fields to be returned.

3. Filtering Fields Using the `fields` Parameter

You can also use the `fields` parameter to filter the fields returned in the search response. This can be useful if you only need specific fields and want to reduce the size of the response. The `fields` parameter accepts an array of field names or wildcard patterns.

For example, to return only the `title` and `author` fields for documents in the `my_index` index, you can use the following search request:

GET /my_index/_search
{
  "query": {
    "match_all": {}
  },
  "fields": ["title", "author"],
  "_source": false
}

Note that the `_source` parameter is set to false in order to not return the source document.

To return all fields with a `text` data type, you can use a wildcard pattern like this:

GET /my_index/_search
{
  "query": {
    "match_all": {}
  },
  "fields": ["*.text"],
  "_source": false
}

4. Displaying Nested Fields

If your index contains nested fields, you can use the dot notation to specify the nested field path in the `fields` parameter. For example, if you have a nested field named `address.city`, you can include it in the search response like this:

GET /my_index/_search
{
  "query": {
    "match_all": {}
  },
  "fields": ["title", "author", "address.city"],
  "_source": false
}

In this example, the search response will include the values of the `title`, `author`, and `address.city` fields.

Conclusion 

In conclusion, displaying fields in an Elasticsearch index can be achieved using the `_mapping` API to retrieve field information and the `_search` API to display field values. You can filter the fields returned in the search response either using the `_source` or `fields` parameters and display nested fields using the dot notation. These techniques can help you understand the structure of your data, identify specific fields, and troubleshoot issues.

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