Conditionally updating a Firestore document in a transaction

Conditionally updating a Firestore document in a transaction

Code sample

Go

ref := client.Collection("cities").Doc("SF")
err := client.RunTransaction(ctx, func(ctx context.Context, tx *firestore.Transaction) error {
	doc, err := tx.Get(ref)
	if err != nil {
		return err
	}
	pop, err := doc.DataAt("population")
	if err != nil {
		return err
	}
	newpop := pop.(int64) + 1
	if newpop <= 1000000 {
		return tx.Set(ref, map[string]interface{}{
			"population": pop.(int64) + 1,
		}, firestore.MergeAll)
	}
	return errors.New("population is too big")
})
if err != nil {
	// Handle any errors in an appropriate way, such as returning them.
	log.Printf("An error has occurred: %s", err)
}

Java

final DocumentReference docRef = db.collection("cities").document("SF");
ApiFuture<String> futureTransaction = db.runTransaction(transaction -> {
  DocumentSnapshot snapshot = transaction.get(docRef).get();
  Long newPopulation = snapshot.getLong("population") + 1;
  // conditionally update based on current population
  if (newPopulation <= 1000000L) {
    transaction.update(docRef, "population", newPopulation);
    return "Population increased to " + newPopulation;
  } else {
    throw new Exception("Sorry! Population is too big.");
  }
});
// Print information retrieved from transaction
System.out.println(futureTransaction.get());

Node.js

const cityRef = db.collection('cities').doc('SF');
try {
  const res = await db.runTransaction(async t => {
    const doc = await t.get(cityRef);
    const newPopulation = doc.data().population + 1;
    if (newPopulation <= 1000000) {
      await t.update(cityRef, { population: newPopulation });
      return `Population increased to ${newPopulation}`;
    } else {
      throw 'Sorry! Population is too big.';
    }
  });
  console.log('Transaction success', res);
} catch (e) {
  console.log('Transaction failure:', e);
}

Python

transaction = db.transaction()
city_ref = db.collection(u'cities').document(u'SF')

@firestore.transactional
def update_in_transaction(transaction, city_ref):
    snapshot = city_ref.get(transaction=transaction)
    new_population = snapshot.get(u'population') + 1

    if new_population < 1000000:
        transaction.update(city_ref, {
            u'population': new_population
        })
        return True
    else:
        return False

result = update_in_transaction(transaction, city_ref)
if result:
    print(u'Population updated')
else:
    print(u'Sorry! Population is too big.')