text: const mongoose = require('mongoose'); 
  mongoose.models = {};
  mongoose.modelSchemas = {};
  
  const ExchangeSchema = new mongoose.Schema({
    name: {
      type: String,
      required: true
    },
    currencies: [{
      type: mongoose.SchemaTypes.ObjectId,
      ref: "Currency"
    }]
  });
  
  module.exports = mongoose.model("Exchange", ExchangeSchema);
  