text: const mongoose = require('mongoose');
  
  const likesSchema = mongoose.Schema({
      username: String,
      userId: { type: mongoose.Schema.Types.ObjectId, ref: 'User' }
  })
  
  const postSchema = new mongoose.Schema({
      user: { type: mongoose.Schema.Types.ObjectId, ref: 'User' },
      photoUrl: String,
      caption: String,
      likes: [likesSchema] // <- one post has many likes
  })
  
  module.exports = mongoose.model('Post', postSchema);