elastic：nested实现对满足条件的数组元素聚合查询

0. 引言

某些业务场景下，我们要对数组元素进行聚合查询，就需要用到nested数据类型，但部分场景是针对数组中指定的元素进行聚合，于是就需要对数组元素进行限定，今天来看看这种场景如何实现。

1. 数据准备

首先我们准备一下模拟数据：一个订单下有各个商品，我们需要统计销售额前3的生鲜商品

mapping如下：

PUT orders 
{"settings": {"number_of_replicas": 0,"number_of_shards": 1},"mappings": {"properties": {"order_no": {"type": "keyword"},"create_user": {"type": "keyword"},"product_list":{"type": "nested","properties": {"name": {"type": "keyword"},"number": {"type": "integer"},"type": {"type": "keyword"}}}}}
}

提供点模拟数据，供大家演练

POST orders/_bulk 
{"index":{}}
{"order_no":"1","create_user":"张三","product_list":[{"name":"苹果", "number":2, "type":"生鲜"},{"name":"水壶", "number":2, "type":"百货"},{"name":"香蕉", "number":4, "type":"生鲜"}]}
{"index":{}}
{"order_no":"2","create_user":"李四","product_list":[{"name":"榴莲", "number":1, "type":"生鲜"},{"name":"小米手机", "number":2, "type":"百货"},{"name":"鲫鱼", "number":5, "type":"生鲜"}]}
{"index":{}}
{"order_no":"2","create_user":"周吴","product_list":[{"name":"苹果", "number":4, "type":"生鲜"},{"name":"香梨", "number":2, "type":"生鲜"},{"name":"毛巾", "number":4, "type":"百货"}]}

2. 实现

以下实现基于elasticsearch 7.13.0版本

1、我们来看直接查询的情况

GET orders/_search
{"size": 0,"aggs": {"product_agg": {"nested": {"path": "product_list"},"aggs": {"name_agg": {"terms": {"field": "product_list.name"},"aggs": {"number_sum": {"sum": {"field": "product_list.number"}},"sort": {"bucket_sort": {"sort": [{"number_sum.value": {"order": "desc"}}],"size": 3}}}}}}}
}

不做商品类型筛选的话，可以看到我们通过nested聚合来实现统计，通过bucket_sort来实现排序，同时再用size参数限定下前3输出，即可实现我们的需求。

nested agg官方文档：https://www.elastic.co/guide/en/elasticsearch/reference/7.13/search-aggregations-bucket-nested-aggregation.html
bucket sort官方文档：https://www.elastic.co/guide/en/elasticsearch/reference/7.13/search-aggregations-pipeline-bucket-sort-aggregation.html

在这里插入图片描述

但是从输出结果很明显的看出，这不是我们想要的结果，我们需要对数组内的type属性做一下筛选，只需要“生鲜”商品

而实现上es中提供了filter参数供我们来筛选聚合元素，我们可以利用它来实现聚合条件的筛选，如下，在官方文档中的filter用法如下：

filter agg 官方文档地址：https://www.elastic.co/guide/en/elasticsearch/reference/7.13/search-aggregations-bucket-filter-aggregation.html

这里需要注意的是，要把嵌套的聚合新写一个agg然后放到filter同级下，也就是作为filter的子聚合；即将filter聚合的结果，作为下一次聚合的入参

GET orders/_search
{"size": 0,"aggs": {"product_agg": {"nested": {"path": "product_list"},"aggs": {"type_filter": {"filter": {"term": {"product_list.type": "生鲜"}},"aggs": {"name_agg": {"terms": {"field": "product_list.name"},"aggs": {"number_sum": {"sum": {"field": "product_list.number"}},"sort": {"bucket_sort": {"sort": [{"number_sum.value": {"order": "desc"}}],"size": 3}}}}}}}}}
}

执行出来的结果如下，符合预期
在这里插入图片描述

另外再附加上java client的实现代码，供大家参考，这里使用了RestHighLevelClient作为客户端

 @Resource
private RestHighLevelClient restClient;public void test() throws IOException {String outAggName = "product_agg";String filterAggName = "type_filter";String termAggName = "name_agg";TermsAggregationBuilder termsAggregationBuilder = AggregationBuilders.terms(termAggName).field("product_list.name");SearchSourceBuilder searchBuilder = new SearchSourceBuilder();searchBuilder.aggregation(AggregationBuilders.nested(outAggName, "product_list").subAggregation(AggregationBuilders.filter(filterAggName, new TermQueryBuilder("product_list.type", "生鲜")).subAggregation(termsAggregationBuilder.subAggregation(AggregationBuilders.sum("number_sum").field("product_list.number")).order(BucketOrder.aggregation("number_sum.value", false)))));searchBuilder.size(0);SearchRequest searchRequest = new SearchRequest("orders");searchRequest.source(searchBuilder);SearchResponse response = restClient.search(searchRequest, RequestOptions.DEFAULT);Map<String, Aggregation> resultMap = response.getAggregations().getAsMap();ParsedNested aggResults = (ParsedNested) resultMap.get(outAggName);ParsedFilter filterAgg = aggResults.getAggregations().get(filterAggName);ParsedStringTerms termAgg = filterAgg.getAggregations().get(termAggName);List<? extends Terms.Bucket> buckets = termAgg.getBuckets();for (Terms.Bucket bucket : buckets) {// TODO 获取分组结果}}