如何在mongodb中获取元素为空的次数以及相同元素的不为空的次数？

Question

我的MongoDB集合中有一个元素“ imageNames ”，有时它具有空值，如何获取具有空值和无时间的次数它是非空的。

[

{
    "_id":{"$oid":"5ce2391c076c4e65d7d6789c"},
    "lotDetails":{
       "produce":"aaa",
       "variety":"default",
       "type":"default",
       "defects":"default"
     },
     "imageNames":[],
 },

 {
        "_id":{"$oid":"5ce2391c076c4e65d7d4563c"},
    "lotDetails":{
        "produce":"aaa",
        "variety":"mixed",
        "type":"default",
        "defects":"default"
    },
    "imageNames":[
        {
            "_id":{"$oid":"5ce2537222295a7bc66354346a"},
            "username":"reshmap222",
            "userData":[
                {
                    "comments":[],
                    "_id":{"$oid":"5ce2537222295a7bc657857b"},
                    "imageName":"11-aaa-868187035222222-1548314329957.jpg",
                    "state":"pending",
                    "imageDate":{"$date":{"$numberLong":"1555744370501"}}
                }
            ]
        }
    ]
 },

 {
    "_id":{"$oid":"5ce2391c076c4e65d7d2345c"},
    "lotDetails":{
        "produce":"aaa",
        "variety":"mixed",
        "type":"default",
        "defects":"default",
    },
    "imageNames":[]
},

{
    "_id":{"$oid":"5ce2391c076c4e65d7d8792c"},
    "lotDetails":{
        "produce":"aaa",
        "variety":"default",
        "type":"default",
        "defects":"default",
    },
    "imageNames":[
        {
            "_id":{"$oid":"5ce2537222295a7bc657857a"},
            "username":"reshmap222",
            "userData":[
                {
                    "comments":[],
                    "_id":{"$oid":"5ce2537222295a7bc657857b"},
                    "imageName":"11-aaa-868187035111111-1548314329957.jpg",
                    "state":"pending",
                    "imageDate":{"$date":{"$numberLong":"1555744370501"}}
                }
            ]
        }
    ]
},

   {
    "_id":{"$oid":"5ce2391c076c4e65d7d3233c"},
    "lotDetails":{
        "produce":"aaa",
        "variety":"mixed",
        "type":"default",
        "defects":"default",
    },
    "imageNames":[],

}

]

预期结果： [

{variety :"mixed",empty : 2, not-empty: 1},
{variety :"default",empty : 1, not-empty: 1}

]

我有来自前端的产品名称来查找元素，在这里我们可以将$ match的产品名称命名为“ aaa”。