title: How to refer multiple schema in my mongoose schema?
body: <p>I am creating a website where you can take and upload tests.
  So there are two kinds of users Company(upload test) and Candidate(take test).
  Now when i create a token how do I refer to both the schema's (schema of company and schema of candidate)?</p>
  
  <pre><code>const mongoose = require("mongoose");
  const { ObjectId } = mongoose.Schema.Types;
  
  let tokenSchema = new mongoose.Schema({
    userId: { type: ObjectId, ref: "&lt;?&gt;" }
  });
  
  module.exports = mongoose.model("Token", tokenSchema);
  </code></pre>