如何在 mongo db 中查找节点的直接子节点

Question

我有以下合集

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}

]

我们抛出任何查询并使用上述数据获取位置的直接节点。

例子。我说的印度应该是 return

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

谢谢

Answer 1

使用Aggregation framework我们可以得到这个想要的结果。

下面的查询给了我们结果，在这个查询中我使用了 $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"}}
])

我的文档在 collection

{ "_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 return 完成状态分组。

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}}
    ])

以上查询结果为

{
        "_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"
                }
        ]
}

如何在 mongo db 中查找节点的直接子节点

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