Elasticsearch：reverse_nested 深度嵌套聚合下的聚合不起作用

Question

Elasticsearch 版本：2.3.3

标题基本上说明了一切。如果在第二个嵌套聚合下使用 reverse_nested，尽管文档似乎通过 reverse_nested 来限定范围（请参阅结果中的最后一个 "doc_count" 字段），但它后面的聚合不会不知何故无法工作。

这里我准备了一个例子——一个文件是一个学生，有入学日期和考试历史。

映射：

{
    "mappings": {
        "students": {
            "properties": {
                "name": {
                    "type": "string"},
                "enrollment": {
                    "type": "date"},
                "exam_histories": {
                    "type": "nested",
                    "properties": {
                        "date": {
                            "type": "date"},
                        "subjects": {
                            "type": "nested",
                            "properties": {
                                "name": {
                                    "type": "string"},
                                "score": {
                                    "type": "short"}}}}}}}}}

测试文档：

{
    "name": "John",
    "enrollment": "2012-09-01T00:00:00+00:00",
    "exam_histories": [
        {
            "date": "2016-05-05T00:00:00+00:00",
            "subjects": [
                {
                    "name": "math",
                    "score": 90}]}]}

聚合查询（无实际意义）：

{
    "aggs": {
        "nested_exam_histories": {
            "nested": {
                "path": "exam_histories"},
            "aggs": {
                "date_buckets": {
                    "date_histogram": {
                        "field": "exam_histories.date",
                        "interval": "day"},
                    "aggs": {
                        "this_reverse_nested_does_work": {
                            "reverse_nested": {},
                            "aggs": {
                                "newest_enrollment": {
                                    "max": {
                                        "field": "enrollment"}}}},
                        "deep_nested_subjects": {
                            "nested": {
                                "path": "exam_histories.subjects"},
                            "aggs": {
                                "score_buckets": {
                                    "terms": {
                                        "field": "exam_histories.subjects.score"},
                                    "aggs": {
                                        "this_reverse_nested_doesnt_work": {
                                            "reverse_nested": {},
                                            "aggs": {
                                                "newest_exam_date": {
                                                    "max": {
                                                        "field": "exam_histories.date"}}}}}}}}}}}}}}

结果：

...
"aggregations" : {
    "nested_exam_histories" : {
      "doc_count" : 1,
      "date_buckets" : {
        "buckets" : [ {
          "key_as_string" : "2016-05-05T00:00:00.000Z",
          "key" : 1462406400000,
          "doc_count" : 1,
          "this_reverse_nested_does_work" : {
            "doc_count" : 1,
            "newest_enrollment" : {
              "value" : 1.3464576E12,
              "value_as_string" : "2012-09-01T00:00:00.000Z"
            }
          },
          "deep_nested_subjects" : {
            "doc_count" : 1,
            "score_buckets" : {
              "doc_count_error_upper_bound" : 0,
              "sum_other_doc_count" : 0,
              "buckets" : [ {
                "key" : 90,
                "doc_count" : 1,
                "this_reverse_nested_doesnt_work" : {
                  "doc_count" : 1,
                  "newest_exam_date" : {
                    "value" : null
                  }
...

...在这里您可以看到聚合 "newest_exam_date" 不起作用。是错误还是我做错了什么？

Answer 1

您需要使用 path 选项明确指定您想要 "reverse-aggregate" 的嵌套对象，否则它假定该字段位于根级别。

来自documentation：

path - Which defines to what nested object field should be joined back. The default is empty, which means that it joins back to the root / main document level. The path cannot contain a reference to a nested object field that falls outside the nested aggregation’s nested structure a reverse_nested is in. Example:

{
     "size":0,
   "aggs": {
      "nested_exam_histories": {
         "nested": {
            "path": "exam_histories"
         },
         "aggs": {
            "date_buckets": {
               "date_histogram": {
                  "field": "exam_histories.date",
                  "interval": "day"
               },
               "aggs": {
                  "this_reverse_nested_does_work": {
                     "reverse_nested": {},
                     "aggs": {
                        "newest_enrollment": {
                           "max": {
                              "field": "enrollment"
                           }
                        }
                     }
                  },
                  "deep_nested_subjects": {
                     "nested": {
                        "path": "exam_histories.subjects"
                     },
                     "aggs": {
                        "score_buckets": {
                           "terms": {
                              "field": "exam_histories.subjects.score"
                           },
                           "aggs": {
                              "this_reverse_nested_doesnt_work": {
                                 "reverse_nested": {
                                    "path": "exam_histories"
                                 },
                                 "aggs": {
                                    "newest_exam_date": {
                                       "max": {
                                          "field": "exam_histories.date"
                                       }
                                    }
                                 }
                              }
                           }
                        }
                     }
                  }
               }
            }
         }
      }
   }
}

结果：

 {
   "took": 5,
   "timed_out": false,
   "_shards": {
      "total": 5,
      "successful": 5,
      "failed": 0
   },
   "hits": {
      "total": 2,
      "max_score": 0,
      "hits": []
   },
   "aggregations": {
      "nested_exam_histories": {
         "doc_count": 2,
         "date_buckets": {
            "buckets": [
               {
                  "key_as_string": "2016-05-05T00:00:00.000Z",
                  "key": 1462406400000,
                  "doc_count": 2,
                  "this_reverse_nested_does_work": {
                     "doc_count": 2,
                     "newest_enrollment": {
                        "value": 1377993600000,
                        "value_as_string": "2013-09-01T00:00:00.000Z"
                     }
                  },
                  "deep_nested_subjects": {
                     "doc_count": 2,
                     "score_buckets": {
                        "doc_count_error_upper_bound": 0,
                        "sum_other_doc_count": 0,
                        "buckets": [
                           {
                              "key": 90,
                              "doc_count": 2,
                              "this_reverse_nested_doesnt_work": {
                                 "doc_count": 2,
                                 "newest_exam_date": {
                                    "value": 1462406400000,
                                    "value_as_string": "2016-05-05T00:00:00.000Z"
                                 }
                              }
                           }
                        ]
                     }
                  }
               }
            ]
         }
      }
   }
}

注意第二个"reverse-aggergation"中的path选项：

reverse_nested": {
    "path": "exam_histories"
 }