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copy_to

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`copy_to`

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The copy_to parameter allows you to copy the values of multiple fields into a group field, which can then be queried as a single field.

If you often search multiple fields, you can improve search speeds by using copy_to to search fewer fields. See Search as few fields as possible.

For example, the first_name and last_name fields can be copied to the full_name field as follows:

response = client.indices.create(
  index: 'my-index-000001',
  body: {
    mappings: {
      properties: {
        first_name: {
          type: 'text',
          copy_to: 'full_name'
        },
        last_name: {
          type: 'text',
          copy_to: 'full_name'
        },
        full_name: {
          type: 'text'
        }
      }
    }
  }
)
puts response

response = client.index(
  index: 'my-index-000001',
  id: 1,
  body: {
    first_name: 'John',
    last_name: 'Smith'
  }
)
puts response

response = client.search(
  index: 'my-index-000001',
  body: {
    query: {
      match: {
        full_name: {
          query: 'John Smith',
          operator: 'and'
        }
      }
    }
  }
)
puts response

PUT my-index-000001
{
  "mappings": {
    "properties": {
      "first_name": {
        "type": "text",
        "copy_to": "full_name" 
      },
      "last_name": {
        "type": "text",
        "copy_to": "full_name" 
      },
      "full_name": {
        "type": "text"
      }
    }
  }
}

PUT my-index-000001/_doc/1
{
  "first_name": "John",
  "last_name": "Smith"
}

GET my-index-000001/_search
{
  "query": {
    "match": {
      "full_name": { 
        "query": "John Smith",
        "operator": "and"
      }
    }
  }
}

	The values of the `first_name` and `last_name` fields are copied to the `full_name` field.
	The `first_name` and `last_name` fields can still be queried for the first name and last name respectively, but the `full_name` field can be queried for both first and last names.

Some important points:

It is the field value which is copied, not the terms (which result from the analysis process).
The original _source field will not be modified to show the copied values.
The same value can be copied to multiple fields, with "copy_to": [ "field_1", "field_2" ]

You cannot copy recursively using intermediary fields. The following configuration will not copy data from field_1 to field_3:

PUT bad_example_index
{
  "mappings": {
    "properties": {
      "field_1": {
        "type": "text",
        "copy_to": "field_2"
      },
      "field_2": {
        "type": "text",
        "copy_to": "field_3"
      },
      "field_3": {
        "type": "text"
      }
    }
  }
}

Instead, copy to multiple fields from the source field:

PUT good_example_index
{
  "mappings": {
    "properties": {
      "field_1": {
        "type": "text",
        "copy_to": ["field_2", "field_3"]
      },
      "field_2": {
        "type": "text"
      },
      "field_3": {
        "type": "text"
      }
    }
  }
}

copy_to is not supported for field types where values take the form of objects, e.g. date_range.

Dynamic mapping

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Consider the following points when using copy_to with dynamic mappings:

If the target field does not exist in the index mappings, the usual dynamic mapping behavior applies. By default, with dynamic set to true, a non-existent target field will be dynamically added to the index mappings.
If dynamic is set to false, the target field will not be added to the index mappings, and the value will not be copied.

If dynamic is set to strict, copying to a non-existent field will result in an error.

If the target field is nested, then copy_to fields must specify the full path to the nested field. Omitting the full path will lead to a strict_dynamic_mapping_exception. Use "copy_to": ["parent_field.child_field"] to correctly target a nested field.

For example:

PUT /test_index
{
  "mappings": {
    "dynamic": "strict",
    "properties": {
      "description": {
        "properties": {
          "notes": {
            "type": "text",
            "copy_to": [ "description.notes_raw"], 
            "analyzer": "standard",
            "search_analyzer": "standard"
          },
          "notes_raw": {
            "type": "keyword"
          }
        }
      }
    }
  }
}

The notes field is copied to the notes_raw field. Targeting notes_raw alone instead of description.notes_raw would lead to a strict_dynamic_mapping_exception.

In this example, notes_raw is not defined at the root of the mapping, but under the description field. Without the fully qualified path, Elasticsearch would interpret the copy_to target as a root-level field, not as a nested field under description.

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