MongoDb 聚合:当给定数组 1 和数组 2 时,如何根据另一个数组 2 对数组 1 进行分组? [英] MongoDb Aggregation: How can I group an array-1 based on another array-2 when given array-1 and array-2?
问题描述
我最初的问题是
MongoDb 聚合:您能否在 $lookup 阶段的管道中 $unwind 输入文档变量?
MongoDb Aggregation: Can you $unwind an input document variable in the pipline of a $lookup stage?
考虑下面的代码:
{$lookup: {
from:"mydoc",
let: {"c":"$myArray"},
pipeline: [
{$unwind: "$$c"},
]
as:"myNewDoc"
}}
如果我愿意,我将如何展开 c
?
How would I unwind c
if I wanted to?
/////原始问题结束
/////END OF ORIGINAL QUESTION
从 Tom Slabbaert 的评论中,我们现在知道可以在 $lookup 阶段的管道中 $unwind 输入文档变量.但不推荐.
From Tom Slabbaert's comment we now know that it is possible to $unwind an input document variable in the pipline of a $lookup stage. But it is not recommended.
我想达到什么目的?
考虑这些集合、poll
和 castedvote
来自 这个答案 来自我问过的一个问题.
Consider these collections, poll
and castedvote
from this answer from a question I had asked.
我正在尝试获得如下输出:
I am trying to get an output like below:
numberOfVotes: 6,
hasThisUserVoted: true,
numberOfComments: 12,
castedVotesPerChoice:{
"choiceA": [
{"_id": ObjectId("..."), "voter": "Juzi", "choice": 0, "pollId": 100 },
{"_id": ObjectId("..."), "voter": "Juma", "choice": 0, "pollId": 100 },
{"_id": ObjectId("..."), "voter": "Jane", "choice": 0, "pollId": 100 },
],
"choiceB": [
{"_id": ObjectId("..."), "voter": "Jamo", "choice": 1, "pollId": 100 },
{"_id": ObjectId("..."), "voter": "Juju", "choice": 1, "pollId": 100 },
{"_id": ObjectId("..."), "voter": "Jana", "choice": 1, "pollId": 100 }
],
"choiceC": [ ]
}
我目前的实现:
db.poll.aggregate([
{"$match": {"_id": 100}},
// ...lookup to get comments
{"$lookup": {
"from":"castedvotes",
"let": {"pollId":"$_id"},
"pipeline":[
{"$match":
{"$expr":
{"$eq": ["$pollId", "$$pollId"]},
}},
],
"as":"votes" // will use this to get number of votes and find out if the authenticated user has voted.
}},
{"$unwind":"$choices"},
{"$lookup": {
"from":"castedvotes",
"let": {"c":"$choices"},
"pipeline":[
{"$match":
{"$expr":
{"$eq": ["$choice", "$$c.id"]},
}},
],
"as":"votesPerChoice"
}},
])
我当前实现的问题是它对同一个集合进行了两次查找,我觉得这是不必要的,它使代码不干燥.使用 $unwind
我知道我可以按照
The issue I have with my current implementation is that it is doing a lookup on the same collection twice I feel like this is unnecessary and it makes the code not dry.
With $unwind
I know I can un-$unwind
as described here.
所以我的问题是如何通过对投票集合进行一次 $lookup 来获得我想要的输出?由于两个查找返回相同的数据.
So my question is how can I get my desired output with one $lookup to the casted vote collection? Since both lookups return the same data.
或者换个方式问这个问题,当给定数组 1 和数组 2 时,如何在 mongodb 聚合中基于另一个数组 2 对数组 1 进行分组?
Or to ask the question differently how can I group an array-1 based on another array-2 in mongodb aggregation when given array-1 and array-2?
这个问题回答了如何通过构造$lookup<在mongodb聚合中根据另一个数组对数组进行分组/code> 以某种方式阶段.它没有回答我的问题.
This question answers how to group arrays based on another array in mongodb aggregation by structuring the $lookup
stage a certain way. It does not answer my question.
推荐答案
如果我已经理解了谜题"正确发布(发布标题和 EDIT 是不同的用例),我们可以通过单个 $lookup
获得所需的结果:
If I've understood the "puzzle" post correctly (Post title and EDIT are different use cases), we can get the desired result with a single $lookup
:
db.poll.aggregate([
{
"$match": {
"_id": 100
}
},
{
"$lookup": {
"from": "castedvotes",
"localField": "pollId",
"foreignField": "choices.id",
"as": "voters"
}
},
{
$project: {
numberOfVotes: {
$size: "$voters"
},
hasThisUserVoted: {
$in: [
"$_id",
"$voters.pollId"
]
},
/**How to calculate it?*/
numberOfComments: {
$multiply: [
{
$size: "$voters"
},
2
]
},
castedVotesPerChoice: {
$arrayToObject: {
$map: {
input: "$choices",
as: "choice",
in: {
k: "$$choice.name",
v: {
$filter: {
input: "$voters",
as: "voter",
cond: {
$eq: [
"$$voter.choice",
"$$choice.id"
]
}
}
}
}
}
}
}
}
}
])
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