mongotemplate group分组查询内嵌数组？

Question

如下所示，我想使用tag分组使用group查询，结果如下，mongotemplate如何写呢？

[
    {
        "id":"5cd392bbb53ac62ba8e8593f",
        "name":"苹果",
        "price":"12.99",
        "description":"苹果家庭的低调皇室",
        "max":"5",
        "num":"5",
        "pictures":[],
        "subMchId":"S0000001",
        "tag":"精选水果",
        "infos":null
    },
    {
        "id":"5cd393dcb53ac61810a67b8e",
        "name":"苹果",
        "price":"12.99",
        "description":"苹果家庭的低调皇室",
        "max":"5",
        "num":"5",
        "pictures":[],
        "subMchId":"S0000001",
        "tag":"精选水果",
        "infos":null
    },
    {
        "id":"5cd39512b53ac60b905d8602",
        "name":"苹果",
        "price":"12.99",
        "description":"苹果家庭的低调皇室",
        "max":"5",
        "num":"5",
        "pictures":[],
        "subMchId":"S0000001",
        "tag":"新鲜蔬菜",
        "infos":null
    }
]

{
    "rawResults":{
        "retval":[
            {
                "tag":"精选水果",
                "collection":[
                    {
                        "id":"5cd392bbb53ac62ba8e8593f",
                        "name":"苹果",
                        "pictures":[]
                    },
                    {
                        "id":"5cd393dcb53ac61810a67b8e",
                        "name":"苹果",
                        "pictures":[]
                    }
                ]
            },
            {
                "tag":"新鲜蔬菜",
                "collection":[
                    {
                        "id":"5cd39512b53ac60b905d8602",
                        "name":"苹果",
                        "pictures":[]
                    }
                ]
            }
        ],
        "count":3,
        "keys":2,
        "ok":1
    },
    "count":3,
    "keys":2,
    "serverUsed":null
}