在mongodb

Question

我有以下文件。

{
    "_id": {
        "$oid": "526fdc1fd6b0a8182300009c"
           },
    "body": "test abc",
    "emb" : [{"body":"text","em":"abc.com","auth":"XYZ"},
             {"body":"text","em":"abc.com","auth":"ABC"}
            ]
}
{
    "_id": {
        "$oid": "526fdc1fd6b0a8182300009d"
           },
    "body": "test abc",
    "emb" : [{"body":"text","em":"abc.com","auth":"PQR"},
             {"body":"text","em":"abc.com","auth":"ABC"}
            ]
}

如果我想计算内部文档数组中每个“auth”的出现次数，我该怎么做？我期待的结果是

"ABC":2
"PQR":1
"XYZ":1

Answer 1

1. $unwind emb数组{$unwind: "$emb"}
2. 在使用emb.auth
计算时按{$group: { _id: "$emb.auth", count: { $sum:1 } } }分组

这为您提供了所需的信息，但语法略有不同：

{ _id:"ABC", count:2 },
{ _id:"PQR", count:1 },
{ _id:"XYZ", count:1 }