mongodb中聚合管道中展开操作后查找阶段不工作
由于在mongodb中相对较新,我使用这三个表执行了聚合管道,令人惊讶的是,我在管道的第三个查找阶段将“r2”数组设置为空mongodb中聚合管道中展开操作后查找阶段不工作,mongodb,flask,Mongodb,Flask,由于在mongodb中相对较新,我使用这三个表执行了聚合管道,令人惊讶的是,我在管道的第三个查找阶段将“r2”数组设置为空 db.user.aggregate([ { $lookup:{ from:"enrollment", localField:"user_id", foreignField:"userID", as:"r
db.user.aggregate([
{
$lookup:{
from:"enrollment",
localField:"user_id",
foreignField:"userID",
as:"r1"
}
},
{
$unwind:{
path:"$r1",
includeArrayIndex:"r1_id"
}
},
{
$lookup:{
from:"course",
localField:"r1.courseID",
foreignField:"courseID",
as:"r2"
}
}
])
我有三个集合,分别是用户、注册和课程
用户身份
> db.user.find()
{ "_id" : ObjectId("5ef4ba8d500ac8876da0d2ca"), "user_id" : 1, "first_name" : "Christian",
"last_name" : "Hur", "email" : "christian@uta.com", "password" : "abc1234" }
{ "_id" : ObjectId("5ef4ba8d500ac8876da0d2cb"), "user_id" : 2, "first_name" : "Mary", "last_name" :
"Jane", "email" : "mary.jane@uta.com", "password" : "password123" }
{ "_id" : ObjectId("5ef4bc2563742adee5403b1d"), "user_id" : 3, "first_name" : "ari", "last_name" :
"dutta", "email" : "dutta@uta.com", "password" : "po1234" }
当然还有
> db.course.find()
{ "_id" : ObjectId("5ef4c1b64a77aec0af5e73ae"), "courseID" : 3333, "title" : "Adv PHP 201",
"description" : "Advance PHP programming", "credits" : 3, "term" : "fall" }
{ "_id" : ObjectId("5ef4c20d4a77aec0af5e73af"), "courseID" : 5555, "title" : "Java 201",
"description" : "Advanced Programming", "credits" : 4, "term" : "fall"}
{ "_id" : ObjectId("5ef4c2564a77aec0af5e73b0"), "courseID" : 6666, "title" : "Angular 1",
"description" : "Intro to Angular", "credits" : 3, "term" : "fall,spring" }
和注册为
> db.enrollment.find()
{ "_id" : ObjectId("5ef771f42d98ffab4460a651"), "userID" : 1, "courseID" : "3333" }
{ "_id" : ObjectId("5ef7722d2d98ffab4460a652"), "userID" : 1, "courseID" : "6666" }
结果
{ "_id" : ObjectId("5ef4ba8d500ac8876da0d2ca"), "user_id" : 1, "first_name" :
"Christian", "last_name" : "Hur", "email" : "christian@uta.com", "password" :
"abc1234", "r1" : { "_id" : ObjectId("5ef771f42d98ffab4460a651"), "userID" :
1, "courseID" : "3333" }, "r1_id" : NumberLong(0), "r2" : [ ] }
{ "_id" : ObjectId("5ef4ba8d500ac8876da0d2ca"), "user_id" : 1, "first_name" :
"Christian", "last_name" : "Hur", "email" : "christian@uta.com", "password" :
"abc1234", "r1" : { "_id" : ObjectId("5ef7722d2d98ffab4460a652"), "userID" :
1, "courseID" : "6666" }, "r1_id" : NumberLong(1), "r2" : [ ] }
我也检查了文档,但没有找到任何帮助,我如何解决这个问题?您在
课程ID
上的集合之间、在注册中以及在课程中都有类型编号
的类型不匹配
将$lookup
更改为:
{
$lookup: {
from: "course",
let: {
courseID: {
$toInt: "$r1.courseID"
}
},
pipeline: [
{
$match: {
$expr: {
$eq: [
"$$courseID",
"$courseID"
]
}
}
}
],
as: "r2"
}
}
你自己试试吧:
另外,既然你说你是新来的,我个人建议你使用\u id
字段,而不是你自己生成的courseID
/用户id
。这只会使它更容易维护
对于Mongo 4.2+版,以下是如何更新注册集合字段:
db.enrollment.updateMany(
{},
[
{
$set: {
courseID: {$toInt: "$courseID"}
}
}
]
)
在你指出后,我才发现字符串和数字不匹配。但是有没有什么方法可以在不干扰其他值的情况下将“enrollment”集合中的所有值更新为number?我添加了关于如何更新整个集合的代码。此语法仅适用于版本4.2+。如果您使用的是较低版本的mongo,则必须对每个文档进行迭代并分别进行更新。