Mappingedit

Mapping is the process of defining how a document, and the fields it contains, are stored and indexed. For instance, use mappings to define:

  • which string fields should be treated as full text fields.
  • which fields contain numbers, dates, or geolocations.
  • the format of date values.
  • custom rules to control the mapping for dynamically added fields.

Mapping Typeedit

Each index has one mapping type which determines how the document will be indexed.

[6.0.0] Deprecated in 6.0.0. See Removal of mapping types .

A mapping type has:

Meta-fields
Meta-fields are used to customize how a document’s metadata associated is treated. Examples of meta-fields include the document’s _index, _type, _id, and _source fields.
Fields or properties
A mapping type contains a list of fields or properties pertinent to the document.

Field datatypesedit

Each field has a data type which can be:

It is often useful to index the same field in different ways for different purposes. For instance, a string field could be indexed as a text field for full-text search, and as a keyword field for sorting or aggregations. Alternatively, you could index a string field with the standard analyzer, the english analyzer, and the french analyzer.

This is the purpose of multi-fields. Most datatypes support multi-fields via the fields parameter.

Settings to prevent mappings explosionedit

Defining too many fields in an index is a condition that can lead to a mapping explosion, which can cause out of memory errors and difficult situations to recover from. This problem may be more common than expected. As an example, consider a situation in which every new document inserted introduces new fields. This is quite common with dynamic mappings. Every time a document contains new fields, those will end up in the index’s mappings. This isn’t worrying for a small amount of data, but it can become a problem as the mapping grows. The following settings allow you to limit the number of field mappings that can be created manually or dynamically, in order to prevent bad documents from causing a mapping explosion:

index.mapping.total_fields.limit
The maximum number of fields in an index. Field and object mappings, as well as field aliases count towards this limit. The default value is 1000.
index.mapping.depth.limit
The maximum depth for a field, which is measured as the number of inner objects. For instance, if all fields are defined at the root object level, then the depth is 1. If there is one object mapping, then the depth is 2, etc. The default is 20.
index.mapping.nested_fields.limit
The maximum number of distinct nested mappings in an index, defaults to 50.
index.mapping.nested_objects.limit
The maximum number of nested JSON objects within a single document across all nested types, defaults to 10000.
index.mapping.field_name_length.limit
Setting for the maximum length of a field name. The default value is Long.MAX_VALUE (no limit). This setting isn’t really something that addresses mappings explosion but might still be useful if you want to limit the field length. It usually shouldn’t be necessary to set this setting. The default is okay unless a user starts to add a huge number of fields with really long names.

Dynamic mappingedit

Fields and mapping types do not need to be defined before being used. Thanks to dynamic mapping, new field names will be added automatically, just by indexing a document. New fields can be added both to the top-level mapping type, and to inner object and nested fields.

The dynamic mapping rules can be configured to customise the mapping that is used for new fields.

Explicit mappingsedit

You know more about your data than Elasticsearch can guess, so while dynamic mapping can be useful to get started, at some point you will want to specify your own explicit mappings.

You can create field mappings when you create an index and add fields to an existing index.

Create an index with an explicit mappingedit

You can use the create index API to create a new index with an explicit mapping.

PUT /my-index
{
  "mappings": {
    "properties": {
      "age":    { "type": "integer" },  
      "email":  { "type": "keyword"  }, 
      "name":   { "type": "text"  }     
    }
  }
}

Creates age, an integer field

Creates email, a keyword field

Creates name, a text field

Add a field to an existing mappingedit

You can use the put mapping API to add one or more new fields to an existing index.

The following example adds employee-id, a keyword field with an index mapping parameter value of false. This means values for the employee-id field are stored but not indexed or available for search.

PUT /my-index/_mapping
{
  "properties": {
    "employee-id": {
      "type": "keyword",
      "index": false
    }
  }
}

Update the mapping of a fieldedit

You can’t change the mapping of an existing field, with the following exceptions:

  • You can add new properties to an object field.
  • You can use the field mapping parameter to enable multi-fields.
  • You can change the value of the ignore_above mapping parameter.

Changing the mapping of an existing field could invalidate data that’s already indexed. If you need to change the mapping of a field, create a new index with the correct mappings and reindex your data into that index. If you only want to rename a field, consider adding an alias field.

View the mapping of an indexedit

You can use the get mapping API to view the mapping of an existing index.

GET /my-index/_mapping

The API returns the following response:

{
  "my-index" : {
    "mappings" : {
      "properties" : {
        "age" : {
          "type" : "integer"
        },
        "email" : {
          "type" : "keyword"
        },
        "employee-id" : {
          "type" : "keyword",
          "index" : false
        },
        "name" : {
          "type" : "text"
        }
      }
    }
  }
}

View the mapping of specific fieldsedit

If you only want to view the mapping of one or more specific fields, you can use the get field mapping API.

This is useful if you don’t need the complete mapping of an index or your index contains a large number of fields.

The following request retrieves the mapping for the employee-id field.

GET /my-index/_mapping/field/employee-id

The API returns the following response:

{
  "my-index" : {
    "mappings" : {
      "employee-id" : {
        "full_name" : "employee-id",
        "mapping" : {
          "employee-id" : {
            "type" : "keyword",
            "index" : false
          }
        }
      }
    }
  }
}