Mapping

store

应用场景：

1. 一个很长的字符串在source内，查询的时候不想通过_source filter从一个很大的_source中获取
2. 当Mapping使用copy_to把内容copy到目标字段的时候,想显示目标字段（这时目标字段在_source内不存在）
   "store": true 表示该字段存储在fields内. "store": false 表示不存储。 比如：

PUT my_index
{
  "mappings": {
    "_doc": {
      "properties": {
        "title": {
          "type": "text",
          "store": true 
        },
        "date": {
          "type": "date",
          "store": true 
        },
        "content": {
          "type": "text"
        }
      }
    }
  }
}
PUT my_index/_doc/1
{
  "title":   "Some short title",
  "date":    "2015-01-01",
  "content": "A very long content field..."
}

则在fields内只存储date和title字段，默认store=false：

{
  "_index": "my_index",
  "_type": "_doc",
  "_id": "1",
  "_version": 2,
  "_score": null,
  "_source": {
    "title": "Some short title",
    "date": "2018-10-01",
    "content": "A very long content field..."
  },
  "fields": {
    "date": [
      "2018-10-01T00:00:00.000Z",
    ],
    "title": [
      "Some short title"
    ]
  },
  "sort": [
    1538352000000
  ]
}