Creates and returns a new Query that includes all documents in the
database that are contained in a collection or subcollection with the
given collectionId.
Executes the given updateFunction and commits the changes applied within
the transaction.
You can use the transaction object passed to 'updateFunction' to read and
modify Firestore documents under lock. You have to perform all reads
before before you perform any write.
Transactions can be performed as read-only or read-write transactions. By
default, transactions are executed in read-write mode.
A read-write transaction obtains a pessimistic lock on all documents that
are read during the transaction. These locks block other transactions,
batched writes, and other non-transactional writes from changing that
document. Any writes in a read-write transactions are committed once
'updateFunction' resolves, which also releases all locks.
If a read-write transaction fails with contention, the transaction is
retried up to five times. The updateFunction is invoked once for each
attempt.
Read-only transactions do not lock documents. They can be used to read
documents at a consistent snapshot in time, which may be up to 60 seconds
in the past. Read-only transactions are not retried.
Transactions time out after 60 seconds if no documents are read.
Transactions that are not committed within than 270 seconds are also
aborted. Any remaining locks are released when a transaction times out.
