下面描述一个场景
如果某个字段的类型是text，在创建索引的时候，针对每个document，对应的这个text字段都会对内容进行分词。由于ES不允许对已经存在的field的类型进行修改，就会导致该字段一直都是会被分词，那么如果之后有需求想对该字段排序，就不行了。具体看下面展示的示例。
PUT /test_index{ "mappings": { "properties": { "field1": { "type": "text" } } }}GET /test_index/_search{ "query": { "match_all": {} }, "sort": [ { "field1": { "order": "desc" } } ]}{ "error": { "root_cause": [ { "type": "illegal_argument_exception", "reason": "Fielddata is disabled on text fields by default. Set fielddata=true on [field1] in order to load fielddata in memory by uninverting the inverted index. Note that this can however use significant memory. Alternatively use a keyword field instead." } ], "type": "search_phase_execution_exception", "reason": "all shards failed", "phase": "query", "grouped": true, "failed_shards": [ { "shard": 0, "index": "test_index", "node": "P-b-TEvyQOylMyEcMEhApQ", "reason": { "type": "illegal_argument_exception", "reason": "Fielddata is disabled on text fields by default. Set fielddata=true on [field1] in order to load fielddata in memory by uninverting the inverted index. Note that this can however use significant memory. Alternatively use a keyword field instead." } } ], "caused_by": { "type": "illegal_argument_exception", "reason": "Fielddata is disabled on text fields by default. Set fielddata=true on [field1] in order to load fielddata in memory by uninverting the inverted index. Note that this can however use significant memory. Alternatively use a keyword field instead.", "caused_by": { "type": "illegal_argument_exception", "reason": "Fielddata is disabled on text fields by default. Set fielddata=true on [field1] in order to load fielddata in memory by uninverting the inverted index. Note that this can however use significant memory. Alternatively use a keyword field instead." } } }, "status": 400}这个时候要想解决这个问题，就可以将一个string field建立两次索引，一个分词用来搜索，一个不分词用来进行排序。
Alternatively use a keyword field instead.
根据错误中的提示，我们重新建立索引
PUT /test_index{ "mappings": { "properties": { "field1": { "type": "text", "fields": { "keyword": { "type": "keyword" } } } } }}GET /test_index/_search{ "query": { "match_all": {} }, "sort": [ { "field1.keyword": { "order": "desc" } } ]}{ "took" : 6, "timed_out" : false, "_shards" : { "total" : 1, "successful" : 1, "skipped" : 0, "failed" : 0 }, "hits" : { "total" : { "value" : 3, "relation" : "eq" }, "max_score" : null, "hits" : [ { "_index" : "test_index", "_type" : "_doc", "_id" : "3", "_score" : null, "_source" : { "field1" : "third" }, "sort" : [ "third" ] }, { "_index" : "test_index", "_type" : "_doc", "_id" : "2", "_score" : null, "_source" : { "field1" : "second" }, "sort" : [ "second" ] }, { "_index" : "test_index", "_type" : "_doc", "_id" : "1", "_score" : null, "_source" : { "field1" : "one" }, "sort" : [ "one" ] } ] }}