"How to get 'parent to child' relation with mongodb aggregation" - node.js

Question

I have one collection called "location". in this collection all child and parent collection are stores. now I want to create a query who returns me parent to child spaces separated string.
Collection
businessId: { type: mongoose.Schema.Types.ObjectId, ref: 'admin' },
parentId: { type: mongoose.Schema.Types.ObjectId, ref: 'location' },
name: { type: String },
image: { type: String },
imageManipulation: { type: String },
locationColor: [{ range: { type: String }, color: { type: String } }],
area: {},
settings: {},
status: { type: String, enum: [0, 1], default: 1 },
isChild: { type: String, enum: [0, 1] },
parentPosition: { type: String }
In the above collection, you can see parentId field. if the location is a child then it have parentId. if the location is a parent then parentId will null. parent location can N level child location.
Collection Data
[{
"_id" : ObjectId("5cee1002a01ad50f5c222982"),
"status" : "1",
"name" : "Ground Floor",
"settings" : {
"zoom" : "0",
"positionX" : "0",
"positionY" : "0",
"width" : "498",
"height" : "498"
},
"image" : "1559105538977.jpg",
"businessId" : ObjectId("5cbd61dc3b56b902284ea388"),
"locationColor" : [],
"updatedAt" : ISODate("2019-05-29T04:52:18.999Z"),
"createdAt" : ISODate("2019-05-29T04:52:18.999Z"),
"__v" : 0
},
{
"_id" : ObjectId("5cee103ca01ad50f5c222983"),
"status" : "1",
"name" : "Kitchen",
"settings" : {
"zoom" : "0",
"positionX" : "0",
"positionY" : "0",
"width" : "498",
"height" : "498"
},
"area" : "{\"type\":3,\"points\":[{\"x\":20,\"y\":178},{\"x\":19,\"y\":75},{\"x\":56,\"y\":71},{\"x\":57,\"y\":52},{\"x\":80,\"y\":18},{\"x\":138,\"y\":17},{\"x\":165,\"y\":52},{\"x\":165,\"y\":94},{\"x\":174,\"y\":96},{\"x\":173,\"y\":179}],\"fill\":\"rgba(178,40,40,0.58)\"}",
"parentId" : ObjectId("5cee1002a01ad50f5c222982"),
"image" : "1559105596975.jpg",
"businessId" : ObjectId("5cbd61dc3b56b902284ea388"),
"locationColor" : [],
"updatedAt" : ISODate("2019-05-29T04:53:16.990Z"),
"createdAt" : ISODate("2019-05-29T04:53:16.990Z"),
"__v" : 0
},
{
"_id" : ObjectId("5cee1078a01ad50f5c222984"),
"status" : "1",
"name" : "Cbot",
"settings" : {
"zoom" : "0",
"positionX" : "0",
"positionY" : "0",
"width" : "498",
"height" : "498"
},
"area" : "{\"type\":3,\"points\":[{\"x\":20,\"y\":311},{\"x\":17,\"y\":59},{\"x\":84,\"y\":58},{\"x\":88,\"y\":312}],\"fill\":\"rgba(20,205,123,0.67)\"}",
"parentId" : ObjectId("5cee103ca01ad50f5c222983"),
"image" : "1559105656049.jpg",
"businessId" : ObjectId("5cbd61dc3b56b902284ea388"),
"locationColor" : [],
"updatedAt" : ISODate("2019-05-29T04:54:16.070Z"),
"createdAt" : ISODate("2019-05-29T04:54:16.070Z"),
"__v" : 0
},
{
"_id" : ObjectId("5cee10c1a01ad50f5c222985"),
"status" : "1",
"name" : "Drower 1",
"settings" : {
"zoom" : "5",
"positionX" : "470",
"positionY" : "70",
"width" : "498",
"height" : "498"
},
"area" : "{\"type\":3,\"points\":[{\"x\":21,\"y\":102},{\"x\":81,\"y\":104},{\"x\":79,\"y\":43},{\"x\":21,\"y\":43}],\"fill\":\"rgba(16,77,193,0.5)\"}",
"parentId" : ObjectId("5cee1078a01ad50f5c222984"),
"image" : "1559105729881.jpg",
"businessId" : ObjectId("5cbd61dc3b56b902284ea388"),
"locationColor" : [],
"updatedAt" : ISODate("2019-05-29T04:55:29.901Z"),
"createdAt" : ISODate("2019-05-29T04:55:29.901Z"),
"__v" : 0
},
{
"_id" : ObjectId("5cee110ea01ad50f5c222986"),
"status" : "1",
"name" : "Drawer 2",
"settings" : {
"zoom" : "5",
"positionX" : "484",
"positionY" : "103",
"width" : "498",
"height" : "498"
},
"area" : "{\"type\":1,\"coordinates\":{\"x\":23,\"y\":125,\"width\":58,\"height\":56},\"points\":[{\"x\":23,\"y\":125},{\"x\":81,\"y\":181}],\"fill\":\"rgba(117,37,109,0.74)\"}",
"parentId" : ObjectId("5cee1078a01ad50f5c222984"),
"image" : "1559105806551.jpg",
"businessId" : ObjectId("5cbd61dc3b56b902284ea388"),
"locationColor" : [],
"updatedAt" : ISODate("2019-05-29T04:56:46.574Z"),
"createdAt" : ISODate("2019-05-29T04:56:46.574Z"),
"__v" : 0
},
{
"_id" : ObjectId("5cee1148a01ad50f5c222987"),
"status" : "1",
"name" : "Drawer 3",
"settings" : {
"zoom" : "5",
"positionX" : "477",
"positionY" : "94",
"width" : "498",
"height" : "498"
},
"area" : "{\"type\":3,\"points\":[{\"x\":22,\"y\":205},{\"x\":20,\"y\":290},{\"x\":84,\"y\":288},{\"x\":85,\"y\":205}],\"fill\":\"rgba(164,108,54,0.57)\"}",
"parentId" : ObjectId("5cee1078a01ad50f5c222984"),
"image" : "1559105864947.jpg",
"businessId" : ObjectId("5cbd61dc3b56b902284ea388"),
"locationColor" : [],
"updatedAt" : ISODate("2019-05-29T04:57:44.972Z"),
"createdAt" : ISODate("2019-05-29T04:57:44.972Z"),
"__v" : 0
},
{
"_id" : ObjectId("5cee5e683b9f67a9f501f818"),
"status" : "1",
"name" : "Washroom",
"settings" : {
"zoom" : "5",
"positionX" : "477",
"positionY" : "94",
"width" : "498",
"height" : "498"
},
"area" : "{\"type\":3,\"points\":[{\"x\":22,\"y\":205},{\"x\":20,\"y\":290},{\"x\":84,\"y\":288},{\"x\":85,\"y\":205}],\"fill\":\"rgba(164,108,54,0.57)\"}",
"parentId" : ObjectId("5cee1002a01ad50f5c222982"),
"image" : "1559105864947.jpg",
"businessId" : ObjectId("5cbd61dc3b56b902284ea388"),
"locationColor" : [],
"updatedAt" : ISODate("2019-05-29T04:57:44.972Z"),
"createdAt" : ISODate("2019-05-29T04:57:44.972Z"),
"__v" : 0
},
{
"_id" : ObjectId("5cee5f593b9f67a9f501fa01"),
"status" : "1",
"name" : "Third Floor",
"settings" : {
"zoom" : "0",
"positionX" : "0",
"positionY" : "0",
"width" : "498",
"height" : "498"
},
"image" : "1559105538977123.jpg",
"businessId" : ObjectId("5cbd61dc3b56b902284ea388"),
"locationColor" : [],
"updatedAt" : ISODate("2019-05-29T04:52:18.999Z"),
"createdAt" : ISODate("2019-05-29T04:52:18.999Z"),
"__v" : 0
}]
Expected result in JSON
[
{
"_id": "5cee1002a01ad50f5c222982",
"name": "Ground Floor"
},
{
"_id": "5cee103ca01ad50f5c222983",
"name": " Kitchen"
},
{
"_id": "5cee1078a01ad50f5c222984",
"name": " Cbot"
},
{
"_id": "5cee110ea01ad50f5c222986",
"name": " Drawer 2"
},
{
"_id": "5cee1148a01ad50f5c222987",
"name": " Drawer 3"
},
{
"_id": "5cee10c1a01ad50f5c222985",
"name": " Drower 1"
},
{
"_id": "5cee5e683b9f67a9f501f818",
"name": " Washroom"
},
{
"_id": "5cee5f593b9f67a9f501fa01",
"name": "Third Floor"
}
]

Answer 1

I do not think you should let mongodb take care of name formatting. So my solution is about finding how many spaces a certain name needs before, so that js can deal with formatting. This is the query:
db.collection.aggregate([
{
$graphLookup: {
from: "collection",
startWith: "$parentId",
connectFromField: "parentId",
connectToField: "_id",
as: "hierarchy"
}
},
{
$project: {
"_id": 1,
"name": 1,
"hierarchy_size": { $size: "$hierarchy" }
}
}
]);
With the $graphLookup, the db is building an in memory graph of edges between connectFromField and connectToField. From the graph you only need the depth of your hierarchy, so I computed hierarchy_size. This is the output:
/* 1 */
{
"_id" : ObjectId("5cee1002a01ad50f5c222982"),
"name" : "Ground Floor",
"hierarchy_size" : 0
}
/* 2 */
{
"_id" : ObjectId("5cee103ca01ad50f5c222983"),
"name" : "Kitchen",
"hierarchy_size" : 1
}
/* 3 */
{
"_id" : ObjectId("5cee1078a01ad50f5c222984"),
"name" : "Cbot",
"hierarchy_size" : 2
}
/* 4 */
{
"_id" : ObjectId("5cee10c1a01ad50f5c222985"),
"name" : "Drower 1",
"hierarchy_size" : 3
}
/* 5 */
{
"_id" : ObjectId("5cee110ea01ad50f5c222986"),
"name" : "Drawer 2",
"hierarchy_size" : 3
}
/* 6 */
{
"_id" : ObjectId("5cee1148a01ad50f5c222987"),
"name" : "Drawer 3",
"hierarchy_size" : 3
}
/* 7 */
{
"_id" : ObjectId("5cee5e683b9f67a9f501f818"),
"name" : "Washroom",
"hierarchy_size" : 1
}
/* 8 */
{
"_id" : ObjectId("5cee5f593b9f67a9f501fa01"),
"name" : "Third Floor",
"hierarchy_size" : 0
}
The only problem here might be query performances, but that depends on how much data you need to process. Also consider the memory limit.