Cross database connection and relationships in mongoDB and nodejs

Question

how can I refer on database's table to another database's table in mongoDB like I have 2 database

1. Root database contain user table
2. company database contain companies table

now I want to refer companies table to user table. is there any possible way to connect this in nodejs and mongodb

Answer 1

You can do like this to populate across databases in mongoose:

import mongoose, { Schema, Types } from "mongoose"

const db1 = mongoose.createConnection('mongodb://127.0.0.1:27017/company');
const db2 = mongoose.createConnection('mongodb://127.0.0.1:27017/root');

const companySchema = new Schema({ name: String });
const Company = db1.model('Company', companySchema);

const userSchema = new Schema({
    name: String,
    company: {
        type: Types.ObjectId,
        ref: Company
    }
})

const User = db2.model('User', userSchema);

const users = await User.find().populate("company")
console.log(users)
db1.close()
db2.close()

result:

[
  {
    _id: new ObjectId("642d5cf980d1e56765814094"),
    name: 'myUser',
    company: {
      _id: new ObjectId("642d5cb580d1e56765814093"),
      name: 'myCompany'
    }
  }
]

From mongosh:

company> db.companies.find()
[ { _id: ObjectId("642d5cb580d1e56765814093"), name: 'myCompany' } ]
company> use root
switched to db root
root> db.users.find()
[
  {
    _id: ObjectId("642d5cf980d1e56765814094"),
    name: 'myUser',
    company: ObjectId("642d5cb580d1e56765814093")
  }
]