组聚合字段“From”必须定义为对象内的表达式

Question

我在数据库安全中有一个收集消息。

为了显示集合结构，我使用此命令。

db.messages.findOne（）

{
    "_id" : ObjectId("4f16fc97d1e2d32371003f02"),
    "body" : "COURTYARD\n\nMESQUITE\n2300 HWY 67\nMESQUITE, TX  75150\ntel: 972-681-3300\nfax: 972-681-3324\n\nHotel Information: http://courtyard.com/DALCM\n\n\nARRIVAL CONFIRMATION:\n Confirmation Number:84029698\nGuests in Room: 2\nNAME: MR ERIC  BASS \nGuest Phone: 7138530977\nNumber of Rooms:1\nArrive: Oct 6 2001\nDepart: Oct 7 2001\nRoom Type: ROOM - QUALITY\nGuarantee Method:\n Credit card guarantee\nCANCELLATION PERMITTED-BEFORE 1800 DAY OF ARRIVAL\n\nRATE INFORMATION:\nRate(s) Quoted in: US DOLLAR\nArrival Date: Oct 6 2001\nRoom Rate: 62.10  per night. Plus tax when applicable\nRate Program: AAA AMERICAN AUTO ASSN\n\nSPECIAL REQUEST:\n NON-SMOKING ROOM, GUARANTEED\n   \n\n\nPLEASE DO NOT REPLY TO THIS EMAIL \nAny Inquiries Please call 1-800-321-2211 or your local\ninternational toll free number.\n \nConfirmation Sent: Mon Jul 30 18:19:39 2001\n\nLegal Disclaimer:\nThis confirmation notice has been transmitted to you by electronic\nmail for your convenience. Marriott's record of this confirmation\nnotice is the official record of this reservation. Subsequent\nalterations to this electronic message after its transmission\nwill be disregarded.\n\nMarriott is pleased to announce that High Speed Internet Access is\nbeing rolled out in all Marriott hotel brands around the world.\nTo learn more or to find out whether your hotel has the service\navailable, please visit Marriott.com.\n\nEarn points toward free vacations, or frequent flyer miles\nfor every stay you make!  Just provide your Marriott Rewards\nmembership number at check in.  Not yet a member?  Join for free at\nhttps://member.marriottrewards.com/Enrollments/enroll.asp?source=MCRE\n\n",
    "filename" : "2.",
    "headers" : {
        "Content-Transfer-Encoding" : "7bit",
        "Content-Type" : "text/plain; charset=us-ascii",
        "Date" : ISODate("2001-07-30T22:19:40Z"),
        "From" : "reservations@marriott.com",
        "Message-ID" : "<32788362.1075840323896.JavaMail.evans@thyme>",
        "Mime-Version" : "1.0",
        "Subject" : "84029698 Marriott  Reservation Confirmation Number",
        "To" : [
            "ebass@enron.com"
        ],
        "X-FileName" : "eric bass 6-25-02.PST",
        "X-Folder" : "\\ExMerge - Bass, Eric\\Personal",
        "X-From" : "Reservations@Marriott.com",
        "X-Origin" : "BASS-E",
        "X-To" : "EBASS@ENRON.COM",
        "X-bcc" : "",
        "X-cc" : ""
    },
    "mailbox" : "bass-e",
    "subFolder" : "personal"
}

我需要得到'from'和'to'对的结果。 为此，我使用aggregate命令。 首先，我使用{"$unwind": "$headers.To"}取消组合来自数组headers.to的所有电子邮件。 比我使用$ group部分来分组我的结果。

我用这个查询：

db.messages.aggregate([{"$unwind": "$headers.To"},
    {"$group": { "_id":null, 'From': "$headers.From", 'To': "$headers.To","count":{$sum:1}}},
    {"$sort": {"count": -1}},
    {"$limit": 10},
    ])

错误信息：

assert: command failed: {
    "ok" : 0,
    "errmsg" : "the group aggregate field 'From' must be defined as an expression inside an object",
    "code" : 15951
} : aggregate failed
_getErrorWithCode@src/mongo/shell/utils.js:25:13
doassert@src/mongo/shell/assert.js:13:14
assert.commandWorked@src/mongo/shell/assert.js:287:5
DBCollection.prototype.aggregate@src/mongo/shell/collection.js:1312:5
@(shell):1:1

2016-11-24T20:07:50.827+0200 E QUERY    [thread1] Error: command failed: {
    "ok" : 0,
    "errmsg" : "the group aggregate field 'From' must be defined as an expression inside an object",
    "code" : 15951
} : aggregate failed :
_getErrorWithCode@src/mongo/shell/utils.js:25:13
doassert@src/mongo/shell/assert.js:13:14
assert.commandWorked@src/mongo/shell/assert.js:287:5
DBCollection.prototype.aggregate@src/mongo/shell/collection.js:1312:5
@(shell):1:1

我做错了什么？

Answer 1

您想要实现的目标 - 假设您想要从＆到 - 分组 - 可以使用以下group ：

{"$group": { "_id": {'From': "$headers.From", 'To': "$headers.To"}, "count": {$sum:1}}}

从参考文档：

$组

按一些指定的表达式对文档进行分组，并为每个不同的分组输出到下一个阶段的文档。 输出文档包含一个_id字段，该字段按键包含不同的组。 输出文档还可以包含计算字段，这些字段包含按$ group的_id字段分组的某些累加器表达式的值

累加器表达式是诸如min ， max （每组）， sum （如您所用），数组表达式（由push和addToSet指定）等表达式。

具体来说，错误消息指出您必须使用上述表达式之一作为“ Form字段的值。

如果你不喜欢_id的From和To “squeezed”，你可以稍后通过添加$project阶段来扩展它。