How to find Immediate Child of a node in mongo db - mongodb

Question

I have following Collection
Location Collection
[
{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}
]
Is any query we throw and get immediate node of location using above data.
Example.
When I said India it should be return
India
|---Maharashtra
|---Pune
|---..
|---Nashik
|---Mumbai
Thank you

Answer 1

Using Aggregation framework we can get this desired result.
The below query gives us the result and in this query I have used $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"}}
])
Documents in my 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" }
After executing the above query, the result is
{
"_id" : ObjectId("5b83e4860c35ef57411a575e"),
"location" : "Maharashstra",
"parentLocation" : "India",
"Result" : [
{
"location" : "pune"
},
{
"location" : "nashik"
},
{
"location" : "mumbai"
}
]
}
If we cut down the last $match in our query, then it will return the complete the grouping of states.
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}}
])
The result of the above query is
{
"_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"
}
]
}