尝试对以下集合进行 mongodb 聚合 $lookup 查询:
店铺收藏:
{
"_id" : ObjectId("5b618a57759612021aaa2ed"),
"no" : "23456",
"date" : ISODate("2012-01-04T16:00:00.000+0000"),
"clientId" : "5b55cc5c05546200217ae0f3"
}
客户集合:
{
"_id" : ObjectId("5b55cc5c05546200217ae0f3"),
"title" : "Ms",
"name" : "Jane Marie"
}
查询:
db.getCollection("shop").aggregate([
{ $lookup:
{
from: "client",
localField: "clientId",
foreignField: "_id",
as: "client"
}
}
])
上面的查询最终给出了一个空的患者数组:
{
"_id" : ObjectId("5b618a57759672021aaa2ed"),
"no" : "20190000024274",
"date" : ISODate("2012-01-04T16:00:00.000+0000"),
"clientId" : "5b55cc5c05546200217ae0f3",
"client" : []
}
编辑 :
当尝试使用 id 数组作为本地 Field 进行查找时:
transaconsIds: ["5b61d4320550de077143b763", "5b61d4324450de002143b777"]
通过使用 :
{
$lookup:
{
from: "transcation",
let: { vid: "transaconsIds" },
pipeline: [
{
$match: {
$expr: {
$eq: ["$_id", { $toObjectId: "$$vid" }]
}
}
}
],
as: "transactions"
}
}
这会导致 Mongo 服务器错误。
编辑02:
尝试查找嵌套如下的 localField 时:
"transactions" : [
{
"bill" : {
"soldItemIds" : [
"5b55aabf0550770021097ed2"
]
}
}
]
通过使用 :
{ $unwind : "$transactions"},
{
$lookup:
{
from: "bill",
let: { did: "$transactions.bill.soldItemIds" },
pipeline: [
{
$match: {
$expr: {
$in: ["$_id", {
$map: {
input: "$$did",
in: { $toObjectId: "$$this" }
}
}
]
}
}
}
],
as: "bills"
}
}
这也会导致 Mongo Server 错误。
最佳答案
这应该这样做:
db.shop.aggregate([
{
$lookup:
{
from: "client",
let: { pid: "$clientId" },
pipeline: [
{
$match: {
$expr: {
$eq: ["$_id", { $toObjectId: "$$pid" }]
}
}
}
],
as: "client"
}
},
{
$set: {
client: {
$arrayElemAt: ["$client", 0]
}
}
}
])
更新: id 字符串数组
db.collection.aggregate(
[
{
$lookup:
{
from: "transactions",
let: { vid: "$transactionIds" },
pipeline: [
{
$match: {
$expr: {
$in: ["$_id", {
$map: {
input: "$$vid",
in: { $toObjectId: "$$this" }
}
}
]
}
}
}
],
as: "transactions"
}
}
])
关于当 localField 为字符串且foreignField 为 ObjectId 格式时，Mongodb $lookup，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/61135000/