Mongoose returning empty array after populate() method-CodePudding

Banged my head against the wall for past 3-4 hours and checked countless articles here on StackOverflow but could not get my response to populate an array correctly. Using Express.js with Typescript, MongoDB and mongoose. Issue is when I get a response with all the orders my orderedlines array is empty even though I can check and see the ids are there in MongoDB atlas. Here is the actual response:

[
  {
    "orderedlines": [],
    "_id": "6251c61f7385c349f88fe95a",
    "userId": {
      "favourites": [
        "623b39e684b9baf1109053f8",
        "623b3afada0e7828602c78df",
        "623b3b49da0e7828602c78e7",
        "623b39ba84b9baf1109053f7",
        "623b3b59da0e7828602c78e9"
      ],
      "_id": "62326179b9c85d3fc833d686",
      "orders": [],
      "email": "[email protected]",
      "username": "stef1222",
      "password": "$2b$10$3e5Y/IoyrcJHH3ud6Mn/I.8PfBm2JrEKHwYRd8cQwUaAdz.YkKSMa",
      "firstName": "Stefan",
      "lastName": "Georgiev",
      "image": "https://res.cloudinary.com/dtggdx3hc/image/upload/v1648046254/deqr4chfysogoppafdug.png",
      "isAdmin": false,
      "hasWriteAccess": false,
      "__v": 0
    },
    "totalPrice": 121.99,
    "__v": 0
  }
]

As seen above my userId is being populated successfully with all its properties but orderedlines is failing to populate and it is returned as empty array. If I remove the .populate() it returns an array of objects with ids

My findOrdersForUserId function in orderServices where I assume the problem occurs

const findOrdersForUserId = async (
  userId: string
): Promise<OrderDocument[]> => {
  const ordersToReturn = await Order.find({ userId: userId })
    .sort({ _id: 1 })
    .populate('userId')
    .populate({path:'orderedlines', model:OrderLine})
  return ordersToReturn
}

Here is my Order model:

import mongoose, { Document } from 'mongoose'

export type OrderLine = {
  orderlineId: string
}

export type OrderDocument = Document & {
  userId: string
  orderedlines: OrderLine[]
  totalPrice: number
}

const orderSchema = new mongoose.Schema({
  userId: { type: mongoose.Schema.Types.ObjectId, ref: 'User', required: true },
  totalPrice: Number,
  orderedlines: [
    {
      type: mongoose.Schema.Types.ObjectId,
      ref: 'OrderLine',
    },
  ],
})

export default mongoose.model<OrderDocument>('Order', orderSchema, 'orders')

My OrderLine model:

import mongoose, { Document } from 'mongoose'

export type OrderLineDocument = Document & {
  productId: string
  userId: string
  quantity: number
  price: number
}

const orderLineSchema = new mongoose.Schema({
  quantity: { type: Number, default: 1 },
  price: Number,
  productId: {
    type: mongoose.Schema.Types.ObjectId,
    ref: 'Product',
    required: true,
  },
  userId: {
    type: mongoose.Schema.Types.ObjectId,
    ref: 'User',
    required: true,
  },
})

export default mongoose.model<OrderLineDocument>('OrderLine', orderLineSchema, 'orderlines')

Mongoose version used: [email protected]
Node version: v16.13.0
Mongo Shell version: v5.0.6
Express version: [email protected]

I would list some of the articles I tried to fix my the issue without success:

Edit: All the code is a part of a fork from a repo that is set to private. I am not sure how can I share access/link to the fork for a better preview of the code. Please enlighten me if you would like to see something else or a more specific part of the code.

CodePudding user response：

You defined OrderLine like this:

export type OrderLine = {
  orderlineId: string
}

Then, you specified orderedlines as an array of OrderLine:

orderedlines: OrderLine[]

In your use case, orderedlines are an array of ObjectId and not an array of objects with nested property orderlineId. TypeScript probably do some sort of casting when defining a model.

Try to change orderedlines to be an array of ObjectId and try again?

CodePudding user response：

Answering my own question because I struggled with this a lot and want to help future people reading this question. First of all and really important issue might be if you are not specificying a collection name. In order to specify a collection name add a third argument in your model creation like so:

export default mongoose.model<OrderLineDocument>('OrderLine',orderLineSchema,'orderLines')

Before the third argument mongoose was creating a collection name with a lower-cased plurarized model name - orderlines. But when I was trying to populate my response I was referring to orderLines with a capital L. So heads up always specify your collection name or check your collection name in your MongoDB Shell/ MongoDB Atlas.

Second of all. Always check if the _ids your array/object that you want to populate are correct _ids that exist in your database. If they are non-existent or wrong the response would either contain empty array or even would return error.

For example I was adding this in the beginning when the error was occuring but those _ids were not existing (I had deleted them before but forgot) in my orderLines collection in the first place (you can still add _ids that are not existing if they are the correct _id structure so be aware)

POST http://localhost:5000/api/v1/orders/62326179b9c85d3fc833d686
Content-Type: application/json

{
  "orderedlines":[
      {"_id": "6251be4d4186c34788e4f034"},
      {"_id": "6251be494186c34788e4f030"}
  ],
  "totalPrice":"121.99"
}

Third of all. If you are using TypeScript there are three approaches that work:

Using your own type

export type OrderLine = {
  _id: string
}

export type OrderDocument = Document & {
  userId: string
  orderedlines: OrderLine[],
  totalPrice: number
}

Saying this would be an array of string

export type OrderDocument = Document & {
  userId: string
  orderedlines: string[],
  totalPrice: number
}

Array of ObjectIds

export type OrderDocument = Document & {
  userId: string
  orderedlines: mongoose.Schema.Types.ObjectId[]
  totalPrice: number
}

After all of the above three things are taken in consideration what worked for me in the end was this approach:

const findOrdersForUserId = async (
  userId: string
): Promise<OrderDocument[]> => {
  const ordersToReturn = await Order.find({ userId: userId })
    .sort({ _id: 1 })
    .populate('userId')
    .populate({
      path: 'orderedlines',
      populate: { path: 'productId', model: 'Product' },
    })
  return ordersToReturn
}

And this is a part of the response I am getting just to showcase that both orderedline, productId and userId are being populated correctly

{
        "quantity": 4, //part of a single orderedline object
        "_id": "6251be494186c34788e4f030", //part of a single orderedline object
        "productId": { // beginning of populated productId
          "_id": "623b3b24da0e7828602c78e3",
          "name": "AMY SS14R - TRICKSTER",
          "image": "https://res.cloudinary.com/dtggdx3hc/image/upload/v1648048425/amy-deluxe-stick-steel-r-ss09r10_1000x1000_bfngtl.jpg",
          "price": 1299,
          "__v": 0
        }, // end of populated productId
        "price": 2.99, //part of a single orderedline object
        "__v": 0 //part of a single orderedline object
      }
    ], // end of the orderedline array of objects
    "_id": "6252bfa8dd00081d7c273e4d", // _id of the order
    "userId": { //beginning of populated userId
      "favourites": [
        "623b39e684b9baf1109053f8",
        "623b3afada0e7828602c78df",
        "623b3b49da0e7828602c78e7",
        "623b39ba84b9baf1109053f7",
        "623b3b59da0e7828602c78e9"
      ],