In Metadata: _all Field, we explained that the special _all field indexes the values from all other fields as one big string. Having all fields indexed into one field is not terribly flexible, though. It would be nice to have one custom _all field for the person’s name, and another custom _all field for the address.

Elasticsearch provides us with this functionality via the copy_to parameter in a field mapping:

PUT /my_index
{
    "mappings": {
        "person": {
            "properties": {
                "first_name": {
                    "type":     "string",
                    "copy_to":  "full_name" 
                },
                "last_name": {
                    "type":     "string",
                    "copy_to":  "full_name" 
                },
                "full_name": {
                    "type":     "string"
                }
            }
        }
    }
}

With this mapping in place, we can query the first_name field for first names, the last_name field for last name, or the full_name field for first and last names.

Mappings of the first_name and last_name fields have no bearing on how the full_name field is indexed. The full_name field copies the string values from the other two fields, then indexes them according to the mapping of the full_name field only.