这篇文章主要介绍group by多个字段查询，这方面的资料在全网都非常少，而我这边的需求需要group by三个字段，而不是仅仅一个字段，大大增加了检索资料的难度，还好这问题被我解决了，多亏了公司里的老程序员。

首先自然是在SpringBoot代码中引入ES查询的client

Maven依赖：

    <dependency>
        <groupId>org.elasticsearch.client</groupId>
        <artifactId>elasticsearch-rest-high-level-client</artifactId>
        <version>7.14.0</version>
    </dependency>
    <dependency>
        <groupId>org.elasticsearch</groupId>
        <artifactId>elasticsearch</artifactId>
        <version>7.14.0</version>
    </dependency>
@Autowired
private RestHighLevelClient client;

构建查询请求，并创建查询的Builder，其中的esIndex是个字符串类型，就是ES的索引，然后创建布尔类型查询条件，设置systemId大于0

    SearchRequest searchRequest = new SearchRequest(esIndex);
    SearchSourceBuilder sourceBuilder = new SearchSourceBuilder();

重点来了，我这边需要groupBy3个字段，核心是tableName，另外两个是dataSouceId、systemId，如果按照SQL语句来写的话就是

select count(0) as count from esIndex （where条件暂时用不着） group by tableName, dataSourceId, systemId

这里使用Aggregation（中文意思：聚合）关键字进行聚合分组，然后是最关键的，多个group by不能使用并列Aggregation，必须使用嵌套聚合，采用subAggregation进行嵌套！！

    AggregationBuilder aggregationBuilder = AggregationBuilders.terms("tableName").field("tableName").size(100000);
    TermsAggregationBuilder dataSourceAgg = AggregationBuilders.terms("dataSourceId").field("dataSourceId");
    TermsAggregationBuilder systemIdAgg = AggregationBuilders.terms("systemId").field("systemId");
    dataSourceAgg.subAggregation(systemIdAgg);
    aggregationBuilder.subAggregation(dataSourceAgg);

    sourceBuilder.aggregation(aggregationBuilder);

这里的是tableName聚合套dataSourceId聚合，dataSourceId聚合套systemId聚合，总共三层嵌套。

然后进行搜索

    searchRequest.source(sourceBuilder);
    SearchResponse searchResponse = client.search(searchRequest, RequestOptions.DEFAULT);
    Aggregations aggregations = searchResponse.getAggregations();

然后你会发现

searchResponse.getAggregations();搜出来的值也是一个嵌套，即aggregations嵌套buckets，buckets再嵌套aggregations，aggregations再嵌套buckets，等等以此类推。到最底层的buckets.size()才是要获取的count值，需要把这些最底层的buckets.size()累加起来才是最终需要的count值，够坑爹的不是吗。

像我这边3个聚合字段，就需要2*3-1次for循环才能统计成功（最后一层的aggregations的size是0，不需要for循环统计），而且每层结构都一样，那么就可以采用递归统计了。

递归统计代码如下：

/**
 * 递归统计ES聚合的数量
 * @param aggregations
 * @return
 */
public static long count(Aggregations aggregations) {
    long totalCount = 0L;
    for (Aggregation aggregation : aggregations) {
        Terms terms = (Terms) aggregation;
        List<? extends Terms.Bucket> buckets = terms.getBuckets();
        if (buckets.size() > 0) {
            if (buckets.get(0).getAggregations().iterator().hasNext()) {
                // 如果内部还有aggregation，就继续往下走，不能统计
                for (Terms.Bucket bucket : buckets) {
                    Aggregations aggregationsInners = bucket.getAggregations();
                    if (aggregationsInners == null || aggregationsInners.asList().size() == 0) {
                        System.out.println("进入了aggregationsInners == null || aggregationsInners.asList().size() == 0");
                    } else {
                        totalCount += count(aggregationsInners);
                    }
                }
            } else {
                // 到底了，后面没有新的aggregation，可以统计数据了
                totalCount += buckets.size();
            }
        }
    }
    return totalCount;
}

最后得到的count就是count(0)的值。

完整代码如下：（删除了所有BoolQueryBuilder）

    SearchRequest searchRequest = new SearchRequest(esIndex);
    SearchSourceBuilder sourceBuilder = new SearchSourceBuilder();

    AggregationBuilder aggregationBuilder = AggregationBuilders.terms("tableName").field("tableName").size(100000);
    TermsAggregationBuilder dataSourceAgg = AggregationBuilders.terms("dataSourceId").field("dataSourceId");
    TermsAggregationBuilder systemIdAgg = AggregationBuilders.terms("systemId").field("systemId");
    dataSourceAgg.subAggregation(systemIdAgg);
    aggregationBuilder.subAggregation(dataSourceAgg);

    sourceBuilder.aggregation(aggregationBuilder);
    searchRequest.source(sourceBuilder);

    try {
        SearchResponse searchResponse = client.search(searchRequest, RequestOptions.DEFAULT);
        long count = 0;
        Aggregations aggregations = searchResponse.getAggregations();
        count = EsAggregationUtil.count(aggregations);

        return count;
    } catch (IOException e) {
        e.printStackTrace();
    }
    return 0L;

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