Conditionally updating a Firestore document in a transaction (async)

Conditionally updating a Firestore document in a transaction (async).

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For detailed documentation that includes this code sample, see the following:

• Transactions and batched writes
• Transactions and batched writes

Code sample

Python

To authenticate to Firestore, set up Application Default Credentials. For more information, see Set up authentication for a local development environment.

transaction = db.transaction()
city_ref = db.collection("cities").document("SF")

@firestore.async_transactional
async def update_in_transaction(transaction, city_ref):
    snapshot = await city_ref.get(transaction=transaction)
    new_population = snapshot.get("population") + 1

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

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

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