在 Elasticsearch 上查询每种类型的最新文档

Question

我正在尝试在 Elasticsearch 上运行看似简单的查询，但我似乎无法获得我正在寻找的结果。

这是我正在尝试做的一个简短示例：

我有一个新闻数据库。每条新闻都包含一个来源、一个标题、一个时间戳和一个用户。

我想要获取给定用户的每个可用来源的最后一个（基于时间戳的）标题。

#!/bin/bash

export ELASTICSEARCH_ENDPOINT="http://localhost:9200"

# Create indexes

curl -XPUT "$ELASTICSEARCH_ENDPOINT/news" -d '{
    "mappings": {
        "news": {
            "properties": {
                "source": { "type": "string", "index": "not_analyzed" },
                "headline": { "type": "object" },
                "timestamp": { "type": "date", "format": "date_hour_minute_second_millis" },
                "user": { "type": "string", "index": "not_analyzed" }
            }
        }
    }
}'

# Index documents
curl -XPOST "$ELASTICSEARCH_ENDPOINT/_bulk?refresh=true" -d '
{"index":{"_index":"news","_type":"news"}}
{"user": "John", "source": "CNN", "headline": "Great news", "timestamp": "2015-07-28T00:07:29.000"}
{"index":{"_index":"news","_type":"news"}}
{"user": "John", "source": "CNN", "headline": "More great news", "timestamp": "2015-07-28T00:08:23.000"}
{"index":{"_index":"news","_type":"news"}}
{"user": "John", "source": "ESPN", "headline": "Sports news", "timestamp": "2015-07-28T00:09:32.000"}
{"index":{"_index":"news","_type":"news"}}
{"user": "John", "source": "ESPN", "headline": "More sports news", "timestamp": "2015-07-28T00:10:35.000"}
{"index":{"_index":"news","_type":"news"}}
{"user": "Mary", "source": "Yahoo", "headline": "More news", "timestamp": "2015-07-28T00:11:54.000"}
{"index":{"_index":"news","_type":"news"}}
{"user": "Mary", "source": "Yahoo", "headline": "Crazy news", "timestamp": "2015-07-28T00:12:31.000"}
'

那么，例如，我如何从约翰那里获得最后一个 CNN 和最后一个 ESPN 头条新闻？

我一直在研究多搜索 API，但这意味着我需要事先了解所有来源（在本例中为 CNN 和 ESPN）。

Answer 1

首先，请注意，我必须将 headline 字段的映射更改为 string，因为在您的示例文档中，标题是 strings 而不是 objects。

因此，类似以下的查询会检索到您期望的结果：

curl -XPOST "$ELASTICSEARCH_ENDPOINT/news/_search" -d '{
  "size": 0,
  "query": {
    "filtered": {
      "filter": {
        "term": {
          "user": "John"           <--- filter for user=John
        }
      }
    }
  },
  "aggs": {
    "sources": {
      "terms": {
        "field": "source"          <--- aggregate by source
      },
      "aggs": {
        "latest": {
          "top_hits": {
            "size": 1,             <--- only take the first...
            "_source": [           <--- only the date and headline
               "headline",
               "timestamp"
            ],
            "sort": {
              "timestamp": "desc"  <--- ...and only the latest hit
            }
          }
        }
      }
    }
  }
}'

这将产生如下内容：

{
  ...
  "aggregations" : {
    "sources" : {
      "doc_count_error_upper_bound" : 0,
      "sum_other_doc_count" : 0,
      "buckets" : [ {
        "key" : "CNN",
        "doc_count" : 2,
        "latest" : {
          "hits" : {
            "total" : 2,
            "max_score" : null,
            "hits" : [ {
              "_index" : "news",
              "_type" : "news",
              "_id" : "AU7Sh3VDGDddn2ZNuDVl",
              "_score" : null,
              "_source":{
                  "headline": "More great news", 
                  "timestamp": "2015-07-28T00:08:23.000"
              },
              "sort" : [ 1438042103000 ]
            } ]
          }
        }
      }, {
        "key" : "ESPN",
        "doc_count" : 2,
        "latest" : {
          "hits" : {
            "total" : 2,
            "max_score" : null,
            "hits" : [ {
              "_index" : "news",
              "_type" : "news",
              "_id" : "AU7Sh3VDGDddn2ZNuDVn",
              "_score" : null,
              "_source":{
                   "headline": "More sports news", 
                   "timestamp": "2015-07-28T00:10:35.000"
              },
              "sort" : [ 1438042235000 ]
            } ]
          }
        }
      } ]
    }
  }
}