Node.js MongoDB$查找2级嵌套文档,不使用$unwind
我有以下文件 loanRequest(只写我想投射的密钥) 抵押珠宝Node.js MongoDB$查找2级嵌套文档,不使用$unwind,node.js,mongodb,mongoose,mongodb-query,aggregation-framework,Node.js,Mongodb,Mongoose,Mongodb Query,Aggregation Framework,我有以下文件 loanRequest(只写我想投射的密钥) 抵押珠宝 { "_id": "5f2bf26783f65d33026ea593", "netweight": 8.52, "purity": 19, } 我想要达到的是 { "_id": "5f2bf2b583f65d33026ea603", "lendingpartner"
{
"_id": "5f2bf26783f65d33026ea593",
"netweight": 8.52,
"purity": 19,
}
我想要达到的是
{
"_id": "5f2bf2b583f65d33026ea603",
"lendingpartner": {
/* some keys here */
},
"loans": [
{
"loanid": 40010,
"loanamount": 100000,
"jewels": [
{
"_id": "5f2bf26783f65d33026ea593",
"netweight": 8.52,
"purity": 19,
},
{
"_id": "5f2bf26783f65d33026ea594",
"netweight": 5.2,
"purity": 40,
},
{
"_id": "5f2bf26783f65d33026ea595",
"netweight": 4.52,
"purity": 39,
}
]
}
]
}
由于我希望在每笔贷款的jewels数组中填充jewel详细信息,$unwind
对我没有帮助。(我试着用它做实验)
我以为我可以在loans数组上运行$map
,然后对贷款的每个宝石运行$lookup
(双重映射?),但无法找到可行的解决方案。
无论如何,这似乎不是正确的方法
这是我能想到的最好的结果(远不是我想要的结果)。我正在使用贴图从对象中选择性地拾取关键点
const loanrequests = await db.collection('loanrequest').aggregate([
{ $match: { requester: ObjectID(user.id) } },
{
$project: {
lendingpartner: {
name: 1,
branchname: '$branch.branchname',
},
loans: {
$map: {
input: '$loans',
as: 'loan',
in: {
loanid: '$$loan.loanid',
loanamount: '$$loan.amount',
jewels: '$$loan.jewels',
},
},
},
},
},
/*
* I experimented with unwind here. Tried adding
* { $unwind: '$loans' },
* { $unwind: '$loans.jewels' }
* but it does not give me the result I need (as already said before)
*/
]).toArray();
我想,我需要在投影之前进行$lookup
,但由于文档的两级嵌套结构(首先是loans
数组,然后是loans.jewels
),我很难编写一个可行的解决方案
我今天开始使用mongodb聚合器,在寻找答案的过程中,我偶然发现了一个类似的问题,但它似乎更复杂,因此我更难理解
谢谢 如果你不想通过聚合实现其他目标,你可以使用。在mongoose中填充
LoanReqests
.find(
{requester: user.id},
{name: 1, branch: 1, loans: 1} // Projection
)
.populate('loans.jewels');
如果您必须使用aggregate来执行示例中没有的操作,那么$unwind确实是您的最佳选择,但是$lookup之后的$grouping可以获得您想要的输出。如果这对你不起作用,你能详细说明$unwind的问题是什么吗?我猜这与您的问题中未列出的字段有关
如前一个答案中所述,$unwind
,然后是$group
,应该是一种方法
当然,在分组之前(我认为这是“未读取”运行unwind的结果),我需要运行$lookup
,以填充loans.jewels
下面是在前面答案的基础上构建的整个解决方案
const loanRequests = await db.collection('loanRequest').aggregate([
{ $match: { requester: ObjectID(user.id) } },
{
$project: {
lender: '$lendingpartner.name',
branch: '$lendingpartner.branch.branchname',
loans: 1,
},
},
{ $unwind: '$loans' },
{
$lookup: {
localField: 'loans.jewels',
from: 'pledgedJewel',
foreignField: '_id',
as: 'loans.jewels',
},
},
{
$group: {
_id: '$_id',
branch: { $first: '$branch' },
lender: { $first: '$lender' },
loans: { $push: '$loans' },
},
},
{
$project: {
_id: 1,
branch: 1,
lender: 1,
loans: 1,
},
},
]).toArray();
类型不匹配的问题 另一个问题是,由于类型不匹配,我的
$lookup
无法工作。在我正在运行聚合的loanRequest集合中,loans.jewels
中的id属于string
类型,而质押Jewel中的外部字段\U id
是ObjectId
这可以通过使用$toObjectId
或$toString
解决(仅在mongodb版本>=4.0中受支持)
但是,我运行的是更低版本的mongodb,因此这些聚合对我来说不起作用。唯一的解决办法是将loans.jewels
的类型更改为ObjectId
,而不是像我那样将其保留为string
更多关于类型不匹配的信息
你说得对,
$unwind
后跟$group
将获得所需的输出。之前我没有意识到$group
,我对如何“unpread”(在运行$unwind之后)一无所知。我试着建立你的解决方案,并得到了预期的结果。
db.loanRequests.aggregate([
{
$project: {
name: 1,
loans: 1,
branch: "$branch.name"
}
},
{
$unwind: "$loans"
},
{
$lookup: {
localField: "loans.jewels",
foreignField: "_id",
from: "jewels",
as: "loans.jewels"
}
},
{
$group: {
_id: "$_id",
name: {
$first: "$name"
},
branch: {
$first: "$branch"
},
loans: {
$push: "$loans"
}
}
}
])
const loanRequests = await db.collection('loanRequest').aggregate([
{ $match: { requester: ObjectID(user.id) } },
{
$project: {
lender: '$lendingpartner.name',
branch: '$lendingpartner.branch.branchname',
loans: 1,
},
},
{ $unwind: '$loans' },
{
$lookup: {
localField: 'loans.jewels',
from: 'pledgedJewel',
foreignField: '_id',
as: 'loans.jewels',
},
},
{
$group: {
_id: '$_id',
branch: { $first: '$branch' },
lender: { $first: '$lender' },
loans: { $push: '$loans' },
},
},
{
$project: {
_id: 1,
branch: 1,
lender: 1,
loans: 1,
},
},
]).toArray();
{ $project: { jewelObjId: { $toObjectId: '$loans.jewels' } } }, // for mongodb >= 4.0
{
$lookup: {
localField: 'jewelObjId', // for mongodb >= 4.0
from: 'pledgedjewel',
foreignField: '_id',
as: 'loans.jewels',
},
},