如何在 mongo db 中找到节点的直系子节点

Question

>我有以下集合

位置集合

[
{id : 1 name : 'l1' , 'location' : pune , parentLocation : Maharashstra},
{id : 2 name : 'l2' , 'location' : nashik , parentLocation : Maharashstra},
{id : 3 name : 'l3' , 'location' : mumbai , parentLocation : Maharashstra},
{id : 4 name : 'l4' , 'location' : Maharashstra , parentLocation : India},
{id : 5 name : 'l5' , 'location' : India , parentLocation : null}
]

是我们抛出的任何查询并使用上述数据获取位置的即时节点。

例。 当我说印度应该回来时

India
|---Maharashtra
|---Pune
|---..
|---Nashik
|---Mumbai

谢谢

Answer 1

使用聚合框架，我们可以得到这个想要的结果。

下面的查询为我们提供了结果，在此查询中，我使用了$lookup、$match$project

db.location.aggregate([
{ 
$lookup: {
from: "location", 
localField: "location", 
foreignField: "parentLocation", 
as:"Result"
} 
},
{$match:{ "Result": {$exists:true, $ne:[]}, parentLocation: {$ne: null} }}, 
{$project :{ parentLocation:1, location:1, "Result.location":1}},
{$match: {location: "Maharashstra"}}
])

我收藏中的文档

{ "_id" : ObjectId("5b83e4860c35ef57411a575b"), "id" : 1, "name" : "l1", "location" : "pune", "parentLocation" : "Maharashstra" }
{ "_id" : ObjectId("5b83e4860c35ef57411a575c"), "id" : 2, "name" : "l2", "location" : "nashik", "parentLocation" : "Maharashstra" }
{ "_id" : ObjectId("5b83e4860c35ef57411a575d"), "id" : 3, "name" : "l3", "location" : "mumbai", "parentLocation" : "Maharashstra" }
{ "_id" : ObjectId("5b83e4860c35ef57411a575e"), "id" : 4, "name" : "l4", "location" : "Maharashstra", "parentLocation" : "India" }
{ "_id" : ObjectId("5b83e4860c35ef57411a575f"), "id" : 5, "name" : "l5", "location" : "India", "parentLocation" : null }
{ "_id" : ObjectId("5b83fec90c35ef57411a5760"), "id" : 6, "name" : "l6", "location" : "Chennai", "parentLocation" : "Tamilnadu" }
{ "_id" : ObjectId("5b83fec90c35ef57411a5761"), "id" : 7, "name" : "l7", "location" : "Trichy", "parentLocation" : "Tamilnadu" }
{ "_id" : ObjectId("5b83fec90c35ef57411a5762"), "id" : 8, "name" : "l8", "location" : "Alapuzha", "parentLocation" : "Kerala" }
{ "_id" : ObjectId("5b83fec90c35ef57411a5763"), "id" : 9, "name" : "l9", "location" : "Kerala", "parentLocation" : "India" }
{ "_id" : ObjectId("5b83fec90c35ef57411a5764"), "id" : 10, "name" : "l10", "location" : "Tamilnadu", "parentLocation" : "India" }

执行上述查询后，结果为

{
"_id" : ObjectId("5b83e4860c35ef57411a575e"),
"location" : "Maharashstra",
"parentLocation" : "India",
"Result" : [
{
"location" : "pune"
},
{
"location" : "nashik"
},
{
"location" : "mumbai"
}
]
}

如果我们减少查询中的最后一个$match，那么它将返回完整的状态分组。

db.location.aggregate([
{ 
$lookup: {
from: "location", 
localField: "location", 
foreignField: "parentLocation", 
as:"Result"
} 
},
{$match:{ "Result": {$exists:true, $ne:[]}, parentLocation: {$ne: null} }}, 
{$project :{ parentLocation:1, location:1, "Result.location":1}}
])

上述查询的结果是

{
"_id" : ObjectId("5b83e4860c35ef57411a575e"),
"location" : "Maharashstra",
"parentLocation" : "India",
"Result" : [
{
"location" : "pune"
},
{
"location" : "nashik"
},
{
"location" : "mumbai"
}
]
}
{
"_id" : ObjectId("5b83fec90c35ef57411a5763"),
"location" : "Kerala",
"parentLocation" : "India",
"Result" : [
{
"location" : "Alapuzha"
}
]
}
{
"_id" : ObjectId("5b83fec90c35ef57411a5764"),
"location" : "Tamilnadu",
"parentLocation" : "India",
"Result" : [
{
"location" : "Chennai"
},
{
"location" : "Trichy"
}
]
}