我的ES文档结构是这样的：

{
"_index": "my_index",
"_type": "_doc",
"_id": "1296",
"_version": 1,
"_seq_no": 431,
"_primary_term": 1,
"_routing": "1296",
"found": true,
"_source": {
    "id": 1296,
    "test_name": "abc"
    "test_id": 513
    "inventory_arr"[
        {
            "city": "bangalore",
            "after_tat": 168,
            "before_tat": 54,
            "popularity_score": 15,
            "rank": 0,
            "discounted_price": 710,
            "labs": [
                {
                    "lab_id": 395,
                    "lab_name": "Prednalytics Laboratory",
                    "lab_rating": 34,
                },
                {
                    "lab_id": 363,
                    "lab_name": "Neuberg Diagnostics",
                    "lab_rating": 408,
                }
            ]
        },
        {
            "city": "mumbai",
            "after_tat": 168,
            "before_tat": 54,
            "popularity_score": 15,
            "rank": 0,
            "discounted_price": 710,
            "labs": [
                {
                    "lab_id": 395,
                    "lab_name": "Prednalytics Laboratory",
                    "lab_rating": 34,
                },
                {
                    "lab_id": 380,
                    "lab_name": "Neuberg Diagnostics",
                    "lab_rating": 408,
                }
            ]
        }
    ]
}

}
我想知道班加罗尔的每个实验室做了多少测试。我面临的问题是：如果使用嵌套聚合按lab_id分组，则按每个实验室分组，而不管它在哪个城市。
假设我的文档中只有一条记录，那么我期待班加罗尔市的答案如下

[
{key: 395, doc_count: 1}
{key: 363, doc_count: 1}
]

注：实验室ID在每个城市可以重复。