Mongo db Query以过滤文档中的嵌套对象数组

Question

我有以下文件

{
    "userid": "5a88389c9108bf1c48a1a6a7",
    "email": "abc@gmail.com",
    "lastName": "abc",
    "firstName": "xyz",
    "__v": 0,
    "friends": [{
        "userid": "5a88398b9108bf1c48a1a6a9",
        "ftype": "SR",
        "status": "ACCEPT",
        "_id": ObjectId("5a9585b401ef0033cc8850c7")
    },
    {
        "userid": "5a88398b9108bf1c48a1a6a91111",
        "ftype": "SR",
        "status": "ACCEPT",
        "_id": ObjectId("5a9585b401ef0033cc8850c71111")
    },
    {
        "userid": "5a8ae0a20df6c13dd81256e0",
        "ftype": "SR",
        "status": "pending",
        "_id": ObjectId("5a9641fbbc9ef809b0f7cb4e")
    }]
},
{
    "userid": "5a88398b9108bf1c48a1a6a9",
    "friends": [{ }],
    "lastName": "123",
    "firstName": "xyz",
    .......
},
{
    "userid": "5a88398b9108bf1c48a1a6a91111",
    "friends": [{ }],
    "lastName": "456",
    "firstName": "xyz",
    ...
}   

• 第一个查询

在这里，我想从朋友数组中获取 userId，其状态等于“接受”。IE

 [5a88398b9108bf1c48a1a6a9,5a88398b9108bf1c48a1a6a91111] 

• 第二次查询

之后，我必须对同一个集合进行另一个查询，以获取第一个查询中返回的每个用户 ID 的详细信息。最终查询将返回[5a88398b9108bf1c48a1a6a9,5a88398b9108bf1c48a1a6a91111] 两个用户 ID 的详细信息， 即

[
        {
         userid" : "5a88398b9108bf1c48a1a6a9",
         "lastName" : "123",
         "firstName" : "xyz"
         },
       {
         "userid" : "5a88398b9108bf1c48a1a6a91111",
          "lastName" : "456",
           "firstName" : "xyz"
       }
   ]

到目前为止我已经尝试过

 Users.find ({'_id':5a88389c9108bf1c48a1a6a7,"friends.status":'ACCEPT'}, (error, users) => {})  
   or 


 Users.find ({'_id':5a88389c9108bf1c48a1a6a7, friends: { $elemMatch: { status: 'ACCEPT' } } }, (error, users) => {})

Answer 1

使用聚合框架$map和$filter运算符来处理任务。$filter将根据状态应等于的指定条件过滤朋友数组"ACCESS"，并将$map结果从过滤后的数组转换为所需的格式。

对于第二个查询，附加一个$lookup管道步骤，该步骤对用户集合进行自连接，以检索与前一个管道中的 id 匹配的文档。

运行以下聚合操作将生成所需的数组：

User.aggregate([
    { "$match": { "friends.status": "ACCEPT" } },
    { "$project": {
            "users": {
                "$map": {
                    "input": {
                        "$filter": {
                            "input": "$friends",
                            "as": "el",
                            "cond": { "$eq": ["$$el.status", "ACCEPT"] }
                        }
                    },
                    "as": "item",
                    "in": "$$item.userid"
                }
            }
    } },
    { "$lookup": {  
        "from": "users",
        "as": "users",
        "localField": "users",
        "foreignField": "userid"
    } },
]).exec((err, results) => {
    if (err) throw err;
    console.log(results[0].users); 
});