text: const mongoose = require('mongoose');
  const Schema = mongoose.Schema;
  const ObjectId = mongoose.Schema.Types.ObjectId;
  
  const transactionSchema = new Schema({
      amount:  {type:Number, required:[true, '¡Aguas! Necesitas ingresar la cantidad de dinero que se gastó']},
      desc:    {type:String},
      date:    {type: Date, required:[true, 'Necesitas especificar la fecha de la transacción']},
      cat:     {type:ObjectId, ref:'Category'},
      account: {type:ObjectId, ref:'Account'},
      user_id: {type:ObjectId, ref:'User'}
  });
  
  module.exports = mongoose.model('Transaction', transactionSchema);