Mongoose Schema - How to add an order attribute for sorting - express

Question

I am currently building a web application where you can create setlists (arrays) with an array of lyric objectId's inside, that you can then sort / order into how you want it. So if you would like the 3rd list item to become the first, then you simply drag and drop it to the first line.
I now have a problem in my mongoose schema. I am looking for a way to implement an order attribute or something that would allow me to add a order value such as 0 or 1 depending on the position of the lyrics. Does any of you know how to best implement such order?
Here is a copy of my schema. Currently lyrics is an array of lyric objectId's. But in there i would need an "Order" as well, so that i can sort the array according to the order value.
const mongoose = require("mongoose");
const SetlistSchema = new mongoose.Schema({
setlistName: { type: String, required: true },
lastEdited: { type: Date },
createdAt: { type: Date, default: Date.now },
lyrics: [{
type: mongoose.Schema.Types.ObjectId,
ref: 'Lyric'
}],
author: {
id: {
type: mongoose.Schema.Types.ObjectId,
ref: "User"
},
username: String
}
});
module.exports = mongoose.model("Setlist", SetlistSchema);
Here is the Lyrics schema.
const mongoose = require("mongoose");
const LyricSchema = new mongoose.Schema({
lyricName: { type: String, required: true },
lyricContent: { type: String, required: true },
lastEdited: { type: Date },
createdAt: { type: Date, default: Date.now },
author: {
id: {
type: mongoose.Schema.Types.ObjectId,
ref: "User"
},
username: String
}
});
module.exports = mongoose.model("Lyric", LyricSchema);
If adding an order number isn't the best practice, what can you then recommend as a way of keeping track of which order the user would like the lyrics to show up?

Answer 1

You can use aggregation framework to sort lyrics by order field. You first need to add a sort field with Number type.
Setlist.aggregate([
{
$unwind: "$lyrics"
},
{
$lookup: {
from: "lyrics", // MUST be the PHYSICAL collection name
localField: "lyrics",
foreignField: "_id",
as: "lyrics"
}
},
{
$sort: {
"lyrics.order": 1
}
},
{
"$group": {
"_id": "$_id",
"lyrics": {
"$push": "$lyrics"
},
"allFields": {
"$first": "$$ROOT"
}
}
},
{
"$replaceRoot": {
"newRoot": {
"$mergeObjects": [
"$allFields",
{
"lyrics": "$lyrics"
}
]
}
}
}
])
Playground
Sample documents:
db={
"lists": [
{
"_id": ObjectId("5a934e000102030405000000"),
"setlistName": "list1",
"lastEdited": ISODate("2020-03-18T23:11:56.443+03:00"),
"createdAt": ISODate("2020-03-15T23:11:56.443+03:00"),
"lyrics": [
ObjectId("6a934e000102030405000000"),
ObjectId("6a934e000102030405000001"),
ObjectId("6a934e000102030405000002")
]
},
{
"_id": ObjectId("5a934e000102030405000001"),
"setlistName": "list2",
"lastEdited": ISODate("2020-03-11T23:11:56.443+03:00"),
"createdAt": ISODate("2020-03-11T23:11:56.443+03:00"),
"lyrics": [
ObjectId("6a934e000102030405000003"),
ObjectId("6a934e000102030405000004")
]
}
],
"lyrics": [
{
"_id": ObjectId("6a934e000102030405000000"),
"name": "Lyric 1",
"order": 3
},
{
"_id": ObjectId("6a934e000102030405000001"),
"name": "Lyric 2",
"order": 1
},
{
"_id": ObjectId("6a934e000102030405000002"),
"name": "Lyric 3",
"order": 2
},
{
"_id": ObjectId("6a934e000102030405000003"),
"name": "Lyric 4",
"order": 2
},
{
"_id": ObjectId("6a934e000102030405000004"),
"name": "Lyric 5",
"order": 1
}
]
}
Output: (as you see lyrics are sorted by order field value)
[
{
"_id": ObjectId("5a934e000102030405000000"),
"createdAt": ISODate("2020-03-15T20:11:56.443Z"),
"lastEdited": ISODate("2020-03-18T20:11:56.443Z"),
"lyrics": [
[
{
"_id": ObjectId("6a934e000102030405000001"),
"name": "Lyric 2",
"order": 1
}
],
[
{
"_id": ObjectId("6a934e000102030405000002"),
"name": "Lyric 3",
"order": 2
}
],
[
{
"_id": ObjectId("6a934e000102030405000000"),
"name": "Lyric 1",
"order": 3
}
]
],
"setlistName": "list1"
},
{
"_id": ObjectId("5a934e000102030405000001"),
"createdAt": ISODate("2020-03-11T20:11:56.443Z"),
"lastEdited": ISODate("2020-03-11T20:11:56.443Z"),
"lyrics": [
[
{
"_id": ObjectId("6a934e000102030405000004"),
"name": "Lyric 5",
"order": 1
}
],
[
{
"_id": ObjectId("6a934e000102030405000003"),
"name": "Lyric 4",
"order": 2
}
]
],
"setlistName": "list2"
}
]