Let's explore another feature of Elasticsearch, where you can build new fields based on currently available fields.

For Example, if you have fields named first_name and second_name but in the response, you need a field named full_name. You can simply use script_fields.

Define an index mapping with a field that will be used for the runtime field calculation. Here's a sample mapping for an index named my_index:

PUT my_index
{
  "mappings": {
    "properties": {
      "field1": {
        "type": "keyword"
      },
      "field2": {
        "type": "keyword"
      }
    }
  }
}

Index some documents with values in "first_name" and "second_name":

POST my_index/_doc/1
{
  "first_name": "John",
  "second_name": "Doe"
}

POST my_index/_doc/2
{
  "first_name": "Jane",
  "second_name": "Smith"
}

Perform a search query with a script_fields parameter to create the "full_name" runtime field based on the existing fields:

GET my_index/_search
{
  "query": {
    "match_all": {}
  },
  "script_fields": {
    "full_name": {
      "script": {
        "source": "params['_source']['first_name'] + ' ' + params['_source']['second_name']",
        "lang": "painless"
      }
    }
  }
}

The response will include the original documents along with the newly created "full_name" field:

{
  "took": 2,
  "timed_out": false,
  "_shards": {
    "total": 1,
    "successful": 1,
    "skipped": 0,
    "failed": 0
  },
  "hits": {
    "total": {
      "value": 2,
      "relation": "eq"
    },
    "max_score": 1.0,
    "hits": [
      {
        "_index": "my_index",
        "_type": "_doc",
        "_id": "1",
        "_score": 1.0,
        "_source": {
          "first_name": "John",
          "second_name": "Doe"
        },
        "fields": {
          "full_name": [
            "John Doe"
          ]
        }
      },
      {
        "_index": "my_index",
        "_type": "_doc",
        "_id": "2",
        "_score": 1.0,
        "_source": {
          "first_name": "Jane",
          "second_name": "Smith"
        },
        "fields": {
          "full_name": [
            "Jane Smith"
          ]
        }
      }
    ]
  }
}

Thats It! It's simple!

If you have any other ideas or suggestions, please do share them in the comments or connect with me on Twitter.