Initial deposit not persisted to database

[jadnco]

When a new portfolio is created, the initial deposit gets saved as a new transaction. This data shows correctly in the browser at first, but disappears as soon as a refresh occurs. The transaction is not being persisted to the database.

var record = store.createRecord('portfolio', {
      name: newPortfolio.name,
      cash: parseFloat(newPortfolio.cash),
      owner: owner
    }),
    transaction = store.createRecord('transaction', {
      type: 'deposit',
      ticker: null,
      shares: null,
      price: null,
      value: parseFloat(newPortfolio.cash)
    });

// New deposit is pushed
record.get('transactions').pushObject(transaction);

// Portfolio is saved, but new transaction isn't
record.save();

I believe the issue has to do with the asynchronous call of functions. record.save() happens before the new transaction is pushed. Calling the save method within a promise was suggested online, but doing so yields errors:

record.get('transactions').then(function(transactions) {
  transactions.pushObject(transaction);
  record.save();
});

// Uncaught TypeError: record.get(...).then is not a function