Starts a new transaction.

        Example:
            >>> from google.cloud import firestore_v1beta1
            >>>
            >>> client = firestore_v1beta1.FirestoreClient()
            >>>
            >>> database = client.database_root_path('[PROJECT]', '[DATABASE]')
            >>>
            >>> response = client.begin_transaction(database)

        Args:
            database (str): The database name. In the format:
                ``projects/{project_id}/databases/{database_id}``.
            options_ (Union[dict, ~google.cloud.firestore_v1beta1.types.TransactionOptions]): The options for the transaction.
                Defaults to a read-write transaction.

                If a dict is provided, it must be of the same form as the protobuf
                message :class:`~google.cloud.firestore_v1beta1.types.TransactionOptions`
            retry (Optional[google.api_core.retry.Retry]):  A retry object used
                to retry requests. If ``None`` is specified, requests will not
                be retried.
            timeout (Optional[float]): The amount of time, in seconds, to wait
                for the request to complete. Note that if ``retry`` is
                specified, the timeout applies to each individual attempt.
            metadata (Optional[Sequence[Tuple[str, str]]]): Additional metadata
                that is provided to the method.

        Returns:
            A :class:`~google.cloud.firestore_v1beta1.types.BeginTransactionResponse` instance.

        Raises:
            google.api_core.exceptions.GoogleAPICallError: If the request
                    failed for any reason.
            google.api_core.exceptions.RetryError: If the request failed due
                    to a retryable error and retry attempts failed.
            ValueError: If the parameters are invalid.

def begin_transaction(
        self,
        database,
        options_=None,
        retry=google.api_core.gapic_v1.method.DEFAULT,
        timeout=google.api_core.gapic_v1.method.DEFAULT,
        metadata=None,
    ):
        """
        Starts a new transaction.

        Example:
            >>> from google.cloud import firestore_v1beta1
            >>>
            >>> client = firestore_v1beta1.FirestoreClient()
            >>>
            >>> database = client.database_root_path('[PROJECT]', '[DATABASE]')
            >>>
            >>> response = client.begin_transaction(database)

        Args:
            database (str): The database name. In the format:
                ``projects/{project_id}/databases/{database_id}``.
            options_ (Union[dict, ~google.cloud.firestore_v1beta1.types.TransactionOptions]): The options for the transaction.
                Defaults to a read-write transaction.

                If a dict is provided, it must be of the same form as the protobuf
                message :class:`~google.cloud.firestore_v1beta1.types.TransactionOptions`
            retry (Optional[google.api_core.retry.Retry]):  A retry object used
                to retry requests. If ``None`` is specified, requests will not
                be retried.
            timeout (Optional[float]): The amount of time, in seconds, to wait
                for the request to complete. Note that if ``retry`` is
                specified, the timeout applies to each individual attempt.
            metadata (Optional[Sequence[Tuple[str, str]]]): Additional metadata
                that is provided to the method.

        Returns:
            A :class:`~google.cloud.firestore_v1beta1.types.BeginTransactionResponse` instance.

        Raises:
            google.api_core.exceptions.GoogleAPICallError: If the request
                    failed for any reason.
            google.api_core.exceptions.RetryError: If the request failed due
                    to a retryable error and retry attempts failed.
            ValueError: If the parameters are invalid.
        """
        # Wrap the transport method to add retry and timeout logic.
        if "begin_transaction" not in self._inner_api_calls:
            self._inner_api_calls[
                "begin_transaction"
            ] = google.api_core.gapic_v1.method.wrap_method(
                self.transport.begin_transaction,
                default_retry=self._method_configs["BeginTransaction"].retry,
                default_timeout=self._method_configs["BeginTransaction"].timeout,
                client_info=self._client_info,
            )

        request = firestore_pb2.BeginTransactionRequest(
            database=database, options=options_
        )
        if metadata is None:
            metadata = []
        metadata = list(metadata)
        try:
            routing_header = [("database", database)]
        except AttributeError:
            pass
        else:
            routing_metadata = google.api_core.gapic_v1.routing_header.to_grpc_metadata(
                routing_header
            )
            metadata.append(routing_metadata)

        return self._inner_api_calls["begin_transaction"](
            request, retry=retry, timeout=timeout, metadata=metadata
        )