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 comma 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("5ce4f84547e90a0b9c3c4763"),
"name": "Test",
"settings": {
"zoom": "3",
"positionX": "69",
"positionY": "69",
"width": "500",
"height": "334"
},
"parentId": null,
"image": "1558509637101.jpg",
"status": "0",
"businessId": ObjectId("5cbd61dc3b56b902284ea388"),
"locationColor": [],
"updatedAt": ISODate("2019-05-22T12:59:26.013Z"),
"createdAt": ISODate("2019-05-22T07:20:37.112Z"),
"__v": 0
},
{
"_id": ObjectId("5ce50caf09359e1b8ccf5c79"),
"name": "Test sub 1",
"settings": {
"zoom": "3",
"positionX": "48",
"positionY": "3",
"width": "500",
"height": "334"
},
"area": "",
"parentId": ObjectId("5ce4f84547e90a0b9c3c4763"),
"image": "1558514863396.jpg",
"status": "0",
"businessId": ObjectId("5cbd61dc3b56b902284ea388"),
"locationColor": [],
"updatedAt": ISODate("2019-05-22T12:59:21.883Z"),
"createdAt": ISODate("2019-05-22T08:47:43.421Z"),
"__v": 0
},
{
"_id": ObjectId("5ce53977e46da33e6cfdd9d1"),
"name": "Test Sub 2",
"settings": {
"zoom": "5",
"positionX": "0",
"positionY": "0",
"width": "500",
"height": "334"
},
"area": "",
"parentId": ObjectId("5ce50caf09359e1b8ccf5c79"),
"image": "1558526327126.jpg",
"businessId": ObjectId("5cbd61dc3b56b902284ea388"),
"locationColor": [],
"updatedAt": ISODate("2019-05-22T11:58:47.147Z"),
"createdAt": ISODate("2019-05-22T11:58:47.147Z"),
"__v": 0
}]
Expected Result
Test, Test sub 1, Test Sub 2
Expected result in JSON
[{
"_id": ObjectId("5ce4f84547e90a0b9c3c4763"),
"name": "Test",
},
{
"_id": ObjectId("5ce50caf09359e1b8ccf5c79"),
"name": "Test, Test sub 1",
},
{
"_id": ObjectId("5ce53977e46da33e6cfdd9d1"),
"name": "Test, Test sub 1, Test Sub 2",
}]

Answer 1

You basically need $graphLookup for recursive loop over the same collection.
db.location.aggregate([
{ "$graphLookup": {
"from": "location",
"startWith": "$parentId",
"connectFromField": "parentId",
"connectToField": "_id",
"as": "parent"
}},
{ "$project": {
"name": {
"$concat": [
"$name",
{ "$reduce": {
"input": "$parent",
"initialValue": "",
"in": { "$concat": [",", "$$this.name", "$$value"] }
}}
]
}
}}
])
Which will output
[
{
"_id": ObjectId("5ce4f84547e90a0b9c3c4763"),
"name": "Test"
},
{
"_id": ObjectId("5ce50caf09359e1b8ccf5c79"),
"name": "Test sub 1,Test"
},
{
"_id": ObjectId("5ce53977e46da33e6cfdd9d1"),
"name": "Test Sub 2,Test sub 1,Test"
}
]
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