请问如何在attachment类型中使用ik分词器?

{

"settings":{

            "index":{

                "number_of_shards":1,

                "number_of_replicas":0

            }

        },

        "mappings": {

            "doc": {

                "properties": {

                    "file": {

                        "type": "attachment",

                        "fields": {

                            "content": {

                                "type": "text",

                                "analyzer": "ik_max_word",

                                "search_analyzer": "ik_max_word",

                            }

                        }

                    }

                }

            }

        }

}

fp = open('/Users/oubing/test4.pdf', 'rb')

text = base64.b64encode(fp.read())

fp.close()

es.index(index="ai", doc_type="doc", body={"file":text})

res = es.search(index="ai", body={

    "query": {

        "match": {

        "file.content": "中国"

        }

    },

    "highlight": {

        "fields": {

        "file.content": {}

        }

    }

})

for hit in res["hits"]["hits"]:

    print(hit["_id"])