以球员信息为例，player索引的player type包含5个字段，姓名，年龄，薪水，球队，场上位置。
index的mapping为：
"mappings": {
"player": {
"properties": {
"name": {
"index": "not_analyzed",
"type": "string"
},
"age": {
"type": "integer"
},
"salary": {
"type": "integer"
},
"team": {
"index": "not_analyzed",
"type": "string"
},
"position": {
"index": "not_analyzed",
"type": "string"
}
},
"_all": {
"enabled": false
}
}
}
索引中的全部数据：
首先，初始化Builder：
SearchRequestBuilder sbuilder = client.prepareSearch("player").setTypes("player");
接下来举例说明各种聚合操作的实现方法，因为在es的api中，多字段上的聚合操作需要用到子聚合(subAggregation)，初学者可能找不到方法（网上资料比较少，笔者在这个问题上折腾了两天，最后度了源码才彻底搞清楚T_T），后边会特意说明多字段聚合的实现方法。另外，聚合后的排序也会单独说明。
group by/count
例如要计算每个球队的球员数，如果使用SQL语句，应表达如下：
select team, count(*) as player_count from player group by team;
ES的java api：
TermsBuilder teamAgg= AggregationBuilders.terms("player_count ").field("team");
sbuilder.addAggregation(teamAgg);
SearchResponse response = sbuilder.execute().actionGet();
group by多个field
例如要计算每个球队每个位置的球员数，如果使用SQL语句，应表达如下：
select team, position, count(*) as pos_count from player group by team, position;
ES的java api：
TermsBuilder teamAgg= AggregationBuilders.terms("player_count ").field("team");
TermsBuilder posAgg= AggregationBuilders.terms("pos_count").field("position");
sbuilder.addAggregation(teamAgg.subAggregation(posAgg));
SearchResponse response = sbuilder.execute().actionGet();
max/min/sum/avg
例如要计算每个球队年龄最大/最小/总/平均的球员年龄，如果使用SQL语句，应表达如下：
select team, max(age) as max_age from player group by team;
ES的java api：
TermsBuilder teamAgg= AggregationBuilders.terms("player_count ").field("team");
MaxBuilder ageAgg= AggregationBuilders.max("max_age").field("age");
sbuilder.addAggregation(teamAgg.subAggregation(ageAgg));
SearchResponse response = sbuilder.execute().actionGet();
对多个field求max/min/sum/avg
例如要计算每个球队球员的平均年龄，同时又要计算总年薪，如果使用SQL语句，应表达如下：
select team, avg(age)as avg_age, sum(salary) as total_salary from player group by team;
ES的java api：
TermsBuilder teamAgg= AggregationBuilders.terms("team");
AvgBuilder ageAgg= AggregationBuilders.avg("avg_age").field("age");
SumBuilder salaryAgg= AggregationBuilders.avg("total_salary ").field("salary");
sbuilder.addAggregation(teamAgg.subAggregation(ageAgg).subAggregation(salaryAgg));
SearchResponse response = sbuilder.execute().actionGet();
聚合后对Aggregation结果排序
例如要计算每个球队总年薪，并按照总年薪倒序排列，如果使用SQL语句，应表达如下：
select team, sum(salary) as total_salary from player group by team order by total_salary desc;
ES的java api：
TermsBuilder teamAgg= AggregationBuilders.terms("team").order(Order.aggregation("total_salary ", false);
SumBuilder salaryAgg= AggregationBuilders.avg("total_salary ").field("salary");
sbuilder.addAggregation(teamAgg.subAggregation(salaryAgg));
SearchResponse response = sbuilder.execute().actionGet();
需要特别注意的是，排序是在TermAggregation处执行的，Order.aggregation函数的第一个参数是aggregation的名字，第二个参数是boolean型，true表示正序，false表示倒序。
Aggregation结果条数的问题
默认情况下，search执行后，仅返回10条聚合结果，如果想反悔更多的结果，需要在构建TermsBuilder 时指定size：
TermsBuilder teamAgg= AggregationBuilders.terms("team").size(15);
Aggregation结果的解析/输出
得到response后：
Map<String, Aggregation> aggMap = response.getAggregations().asMap();
StringTerms teamAgg= (StringTerms) aggMap.get("keywordAgg");
Iterator<Bucket> teamBucketIt = teamAgg.getBuckets().iterator();
while (teamBucketIt .hasNext()) {
Bucket buck = teamBucketIt .next();
//球队名
String team = buck.getKey();
//记录数
long count = buck.getDocCount();
//得到所有子聚合
Map subaggmap = buck.getAggregations().asMap();
//avg值获取方法
double avg_age= ((InternalAvg) subaggmap.get("avg_age")).getValue();
//sum值获取方法
double total_salary = ((InternalSum) subaggmap.get("total_salary")).getValue();
//...
//max/min以此类推
}
总结
综上，聚合操作主要是调用了SearchRequestBuilder的addAggregation方法，通常是传入一个TermsBuilder，子聚合调用TermsBuilder的subAggregation方法，可以添加的子聚合有TermsBuilder、SumBuilder、AvgBuilder、MaxBuilder、MinBuilder等常见的聚合操作。
从实现上来讲，SearchRequestBuilder在内部保持了一个私有的 SearchSourceBuilder实例， SearchSourceBuilder内部包含一个List<AbstractAggregationBuilder>，每次调用addAggregation时会调用 SearchSourceBuilder实例，添加一个AggregationBuilder。
同样的，TermsBuilder也在内部保持了一个List<AbstractAggregationBuilder>，调用addAggregation方法（来自父类addAggregation）时会添加一个AggregationBuilder。有兴趣的读者也可以阅读源码的实现。
如果有什么问题，欢迎一起讨论，如果文中有什么错误，欢迎批评指正。
注：文中使用的Elastic Search API版本为2.3.2
public List<Map<String, Object>> queryAggregationsByAttr(BoolQueryBuilder boolQueryBld){
List<Map<String, Object>> result = new ArrayList<>();
NestedBuilder nestedBuilder= AggregationBuilders.nested("negstedAttr").path("spuAttrList");
//属性名称分组
TermsBuilder tbName= AggregationBuilders.terms("attrNameAgg").field("spuAttrList.name");
//嵌套查询的子查询中分组count
TermsBuilder tb= AggregationBuilders.terms("attrvIdAgg").field("spuAttrList.attrvId");
//属性值字段
TermsBuilder tbVal= AggregationBuilders.terms("attrValAgg").field("spuAttrList.value");
NestedBuilder all = nestedBuilder.subAggregation(tbName.subAggregation(tb.subAggregation(tbVal)));
NativeSearchQueryBuilder nativeQueryBuilderAgg = new NativeSearchQueryBuilder()
.withQuery(boolQueryBld)
.withIndices("skus").withTypes("skus")
.addAggregation(all);
SearchQuery searchQueryAgg = nativeQueryBuilderAgg.build();
Aggregations aggregations = elasticsearchTemplate.query(searchQueryAgg, new ResultsExtractor<Aggregations>() {
@Override
public Aggregations extract(SearchResponse response) {
return response.getAggregations();
}
});
Map<String, Aggregation> map=aggregations.asMap();
for(String s:map.keySet()){
if("negstedAttr".equals(s)) {
InternalNested internalNested = (InternalNested)map.get(s);
//属性名称
StringTerms nameTerms=(StringTerms) internalNested.getAggregations().get("attrNameAgg");
//属性子表id
for(org.elasticsearch.search.aggregations.bucket.terms.Terms.Bucket tbket:nameTerms.getBuckets()){
//对应一组属性值
Map<String, Object> categoryIdsMapTerms = new HashMap<String, Object>();
categoryIdsMapTerms.put("typeId", "attrValueIds");
categoryIdsMapTerms.put("typeName", tbket.getKeyAsString());
LongTerms attrvIdTerms=(LongTerms)tbket.getAggregations().asMap().get("attrvIdAgg");
if(attrvIdTerms == null || CollectionUtils.isEmpty(attrvIdTerms.getBuckets())) {
continue;
}
List<Map<String, Object>> dataList = new ArrayList<>();
//属性子表val
for(org.elasticsearch.search.aggregations.bucket.terms.Terms.Bucket attrIdB : attrvIdTerms.getBuckets()) {
//dataListMap
Map<String, Object> dataListMap = new HashMap<String, Object>();
Long attrvId = (Long) attrIdB.getKeyAsNumber();
StringTerms valTerms=(StringTerms) attrIdB.getAggregations().asMap().get("attrValAgg");
if(valTerms == null || CollectionUtils.isEmpty(valTerms.getBuckets())) {
continue;
}
String attrValStr = valTerms.getBuckets().get(0).getKeyAsString();
dataListMap.put("id", attrvId);
dataListMap.put("name", attrValStr);
dataList.add(dataListMap);
}
if(!CollectionUtils.isEmpty(dataList)) {
categoryIdsMapTerms.put("dataList", dataList);
}
result.add(categoryIdsMapTerms);
}
}
}
return result;
}
