// TODO: Consider names of GetDocumentSnapshotAsync/GetQuerySnapshotAsync.
// Perhaps just SnapshotDocumentAsync and SnapshotQueryAsync?
// Just using SnapshotAsync overloads feels like a bad idea as they do quite different things.
/// <summary>
/// Fetch a snapshot of the document specified by <paramref name="documentReference"/>, with respect to this transaction.
/// This method cannot be called after any write operations have been created.
/// </summary>
/// <param name="documentReference">The document reference to fetch. Must not be null.</param>
/// <param name="cancellationToken">A cancellation token to monitor for the asynchronous operation.</param>
/// <returns>A snapshot of the given document with respect to this transaction.</returns>
public Task <DocumentSnapshot> GetDocumentSnapshotAsync(DocumentReference documentReference, CancellationToken cancellationToken = default)
{
GaxPreconditions.CheckNotNull(documentReference, nameof(documentReference));
GaxPreconditions.CheckState(_writes.IsEmpty, "Firestore transactions require all reads to be executed before all writes.");
CancellationToken effectiveToken = GetEffectiveCancellationToken(cancellationToken);
return(documentReference.SnapshotAsync(TransactionId, effectiveToken));
}