使用mongodb aggregate groupby

Question

db.getCollection('dbName').aggregate(
{$match: {"Request":"request"}},
{$project : {"PageResult":1,"ProductFilter":1,"BreadCrumbs":1,"ShowCaseHtml":1}},
{$unwind: "$PageResult"},
{$match: { $and:[ 
                {"PageResult.Brand":{$in:[/b1/i,/b2/i]}}
             ]}},
{$group: {"_id": {"Request":"$Request",
    "ProductFilter":"$ProductFilter",
    "BreadCrumbs":"$BreadCrumbs",
    "ShowCaseHtml":"$ShowCaseHtml"},
    "PageResult": {$push : "$PageResult"}}},
{$project : {"PageResult.CategoryID":1}}
)

查询的结果如下：

PageResult" : [ 
        {
            "CategoryID" : "60006410"
        }, 
        {
            "CategoryID" : "60006410"
        }, 
        {
            "CategoryID" : "60006410"
        }, 
        {
            "CategoryID" : "60006410"
        }, 
        {
            "CategoryID" : "60006410"
        }, 
        {
            "CategoryID" : "60006410"
        }, 
        {
            "CategoryID" : "60006410"
        }, 
        {
            "CategoryID" : "60006410"
        }, 
        {
            "CategoryID" : "60006410"
        }, 
        {
            "CategoryID" : "60006410"
        }, 
        {
            "CategoryID" : "60005202"
        }, 
        {
            "CategoryID" : "60005202"
        }, 
        {
            "CategoryID" : "60005202"
        }, 
        {
            "CategoryID" : "60005202"
        }, 
        {
            "CategoryID" : "60005202"
        }, 
        {
            "CategoryID" : "60005202"
        }
    ]

我尝试的是使用CategoryID对PageResult进行分组，所以我在上面的查询中添加了下面这几行：

{$unwind: "$PageResult"},
{ $group : {_id : "$PageResult.CategoryID", count : {$sum : 1} } }

但它给了我这个

{
"_id" : "60005202",
"count" : 6.0
}

我是不是用错了$group，结果不应该是这样的吗

 {
"_id" : "60006410",
"count" : 10.0
}, 
{
"_id" : "60005202",
"count" : 6.0
}

Answer 1

几天前，我更改了C:\Users\username.3T\robo-3t\1.1.1\robo3t.json文件中的批处理大小(批处理大小:1)，所以每次更改时都看到1个结果是很正常的，我认为默认值是50，所以这意味着我的代码运行得很好。