15

MongoDB 聚合每分钟都变得指数级复杂！

我目前是$unwind一个嵌套数组，然后对展开的嵌套数组中的每个对象执行$lookup一个_id。我最后的尝试是用$group. 但是，我无法重建原始嵌入数组及其原始属性名称，以及每个文档的其余原始直接属性。

到目前为止，这是我的尝试：

db.users.aggregate([
    {
        $unwind: "$profile",
        $unwind: {
            path: "$profile.universities",
            preserveNullAndEmptyArrays: true
        }
    },
    {
        $lookup: {
            from: "universities",
            localField: "profile.universities._id",
            foreignField: "_id",
            as: "profile.universities"
        }
    },
    {
        $group: {
            _id: "$_id",
            emails: { "$first": "$emails" },
            profile: { "$first": "$profile" },
            universities: { "$push": "$profile.universities" }
        }
    }
]).pretty()

我得到的是这样的：

{
    "_id" : "A_USER_ID",
    "emails" : [
        {
            "address" : "AN_EMAIL_ADDRESS",
            "verified" : false
        }
    ],
    "profile" : {
        "name" : "NAME",
        "company" : "A COMPANY",
        "title" : "A TITLE",
        "phone" : "123-123-1234",
        "disabled" : false,
        "universities" : [
            {
                "_id" : "ID_1",
                "name" : "UNIVERSITY_NAME_1",
                "code" : "CODE_1",
                "styles" : {AN_OBJECT}
            }
        ]
    },
    "universities" : [
        [
            {
                "_id" : "ID_1",
                "name" : "UNIVERSITY_NAME_1",
                "code" : "CODE_1",
                "styles" : {AN_OBJECT}
            }
        ],
        [
            {
                "_id" : "ID_2",
                "name" : "UNIVERSITY_NAME_2",
                "code" : "CODE_2",
                "styles" : {AN_OBJECT}
            }
        ]
    ]
}

这个结果有两个问题：

  1. 结果universities是一个数组的数组，每个数组都有一个对象，因为返回的是原始嵌套数组$lookup的单个元素数组。$profile.universities它应该只是一个对象数组。
  2. 结果universities应取其原始位置，如嵌套在profiles. 我知道为什么原来profile.universities是这样的，因为我正在使用$first运算符。我的意图是保留 的所有原始属性profile，同时保留原始嵌套universities数组。

最终，我需要的是这样的：

{
    "_id" : "A_USER_ID",
    "emails" : [
        {
            "address" : "AN_EMAIL_ADDRESS",
            "verified" : false
        }
    ],
    "profile" : {
        "name" : "NAME",
        "company" : "A COMPANY",
        "title" : "A TITLE",
        "phone" : "123-123-1234",
        "disabled" : false,
        "universities" : [
            {
                "_id" : "ID_1",
                "name" : "UNIVERSITY_NAME_1",
                "code" : "CODE_1",
                "styles" : {AN_OBJECT}
            },
            {
                "_id" : "ID_2",
                "name" : "UNIVERSITY_NAME_2",
                "code" : "CODE_2",
                "styles" : {AN_OBJECT}
            }
        ]
    }
}

我可以使用另一个运算符来代替$group实现此目的吗？还是我理解$group错误的目的？

编辑：这是原始帖子，上下文： 如果 Mongo $lookup 是左外连接，那么它怎么会排除不匹配的文档？

4

1 回答 1

31

因为$lookup操作符会产生一个数组字段，所以需要$unwind在管道之前新建字段才能$group得到想要的结果：

db.users.aggregate([
    { "$unwind": "$profile" },
    { "$unwind": {
        "path": "$profile.universities",
         "preserveNullAndEmptyArrays": true
    } }, 
    { "$lookup": {
        "from": "universities",
        "localField": "profile.universities._id",
        "foreignField": "_id",
        "as": "universities"
    } },    
    { "$unwind": "$universities" },
    { "$group": {
        "_id": "$_id",
        "emails": { "$first": "$emails" },
        "profile": { "$first": "$profile" },
        "universities": { "$push": "$universities" }
    } },
    { "$project": {
        "emails": 1,  
        "profile.name" : 1,
        "profile.company": 1,
        "profile.title" : 1,
        "profile.phone" : 1,
        "profile.disabled": 1,          
        "profile.universities": "$universities"
    } }
]).pretty()
于 2016-09-14T13:56:04.357 回答