Populate mongo data in another service using aggregate

Question

i have two models in seperate sevices(micro service). How can i use the model in other sevice to populate its data in my aggregation.

I added a clone of user model coming from user service. In other to load the appropriate model like so.

import mongoose, { Schema } from 'mongoose';
import configuration from '../config/config';

 const db = mongoose.createConnection(configuration.mongo.auth_db);
  export const User = db.model(
   'Users',
   new Schema({
     userType: String,
     status: Boolean,
     isVerified: Boolean,
   })
 );
 export const Merchant = db.model(
  'Merchant',
  new Schema({
    isApproved: Boolean,
    storeStatus: String,
    storeUrl: String,
  })
 );

This is the actual model in the wishlist service where i also added the model references

import { Product } from './product';
import { User } from './user';
const WishlistSchema = new Schema<IWishlist>(
  {
    user: {
      type: Schema.Types.ObjectId,
      ref: User,
      required: true,
    },
    products: [
      {
        product: {
          type: Schema.Types.ObjectId,
          ref: Product,
        },
        addedAt: {
          type: Date,
          default: new Date(),
        },
      },
    ],
  },
  {
    timestamps: true,
  }
);

This is what i have in my get wishlist code. The issue is $lookup from accepts only string collection name. And when i try to change it the actual collection name. i.e from: "users", it doesn't work

import { User } from '../models/user';



const wishlist = await Wishlist.aggregate([
  {
    $match: {
      user: new Types.ObjectId(user.id),
    },
  },
  {
    $unwind: '$products',
  },
  {
    $sort: {
      'products.addedAt': -1,
    },
  },
  {
    $lookup: {
      from: User,
      localField: 'user',
      foreignField: '_id',
      as: 'user',
    },
  },
]);