elasticsearch学习笔记（二十九）——Elasticsearch 将一个field索引两次来解决字符串排序问题

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" } } ]