Mapping in Elasticsearch

Mapping serves as the schema definition for an index, similar to table structures in relational databases. Its primary responsibilities include:

1. Declaring field names within the index
2. Specifying data types for each field
3. Configuring inverted index settings

When documents are indexed, Elasticsearch transforms the JSON structure into the flat format required by Apache Lucene.

Field Data Types

Simple Types

• Text / Keyword
• Date
• Integer / Floating
• Boolean
• IPv4 / IPv6

Complex Types

• Object and nested types

Specialized Types

• Geolocation types

Dynamic Mapping

During document creation, Elasticsearch automatically infers field types based on the document content. This dynamic mapping capability eliminates the need to manual schema definition.

Example workflow:

// creating the employee_info index
POST employee_info/_doc
{
  "username":"john",
  "hireDate":"2021-05-14",
  "location":"usa"
}

// retrieving the inferred mapping
GET /employee_info/_mapping

Response structuree:

{
  "employee_info" : {
    "mappings" : {
      "properties" : {
        "hireDate" : {
          "type" : "date"
        },
        "location" : {
          "type" : "text",
          "fields" : {
            "keyword" : {
              "type" : "keyword",
              "ignore_above" : 256
            }
          }
        },
        "username" : {
          "type" : "text",
          "fields" : {
            "keyword" : {
              "type" : "keyword",
              "ignore_above" : 256
            }
          }
        }
      }
    }
  }
}

Dynamic Field Control

The dynamic parameter governs how Elasticsearch handles new fields discovered during indexing:

• true (default): Documents are indexed normally, and new fields become searchable
• false: Documents are indexed, but new fields cannot be searched
• strict: Document indexing is rejected if unknown fields are present

Configuration example:

PUT employee_info/_mapping
{
  "dynamic":"strict"
}

Explicit Mapping Definition

Manual mapping configuraton provides precise control over field behavior:

PUT staff_directory
{
  "mappings": {
    "properties": {
      "firstName": {
        "type": "text"
      },
      "lastName": {
        "type": "text"
      },
      "joinDate": {
        "type": "date",
        "index": false
      }
    }
  }
}