How to highlight date fields in Elasticsearch?

Question

My mapping:

"mappings": {
     "my_type": {
        "properties": {
           "birthDate": {
              "type": "date",
              "format": "dateOptionalTime"
           },
           "name": {
              "type": "string"
           }
        }
     }
}

My search query:

GET my_index/_search
{
  "query": {
    "bool": {
      "should": [
        {
          "match": {
            "name": "babken"
          }
        },
        {
          "term": {
            "birthDate": {
              "value": "1999-01-01"
            }
          }
        }
      ]
    }
  },
  "highlight": {
    "fields": {
      "*": {}
    }
  }
}

However in the response body, only the name field is highlighted, even though the birthDate field has matched as well:

"hits": [
         {
            "_index": "my_index",
            "_type": "my_type",
            "_id": "1a82fbb4-1268-42b9-9999-ef932f67a114",
            "_score": 12.507131,
            "_source": {
               "name": "babken",
               "birthDate": "1999-01-01",
            },
            "highlight": {
               "name": [
                  "<em>babken</em>"
               ]
            }
         }
         ...

How can I make the birthDate field appear in "highlight" results as well if it has matched?

I'm using Elasticsearch 1.6

Answer 1

You would need to change the the type to string to enable highlighting.

Bare minimum requirement for a field to be enabled for highlighting is that it should be string type.

The following issue has little more discussion about it.