Gets multiple documents.

        Documents returned by this method are not guaranteed to be returned in the
        same order that they were requested.

        Example:
            >>> from google.cloud import firestore_v1beta1
            >>>
            >>> client = firestore_v1beta1.FirestoreClient()
            >>>
            >>> database = client.database_root_path('[PROJECT]', '[DATABASE]')
            >>>
            >>> # TODO: Initialize `documents`:
            >>> documents = []
            >>>
            >>> for element in client.batch_get_documents(database, documents):
            ...     # process element
            ...     pass

        Args:
            database (str): The database name. In the format:
                ``projects/{project_id}/databases/{database_id}``.
            documents (list[str]): The names of the documents to retrieve. In the format:
                ``projects/{project_id}/databases/{database_id}/documents/{document_path}``.
                The request will fail if any of the document is not a child resource of
                the given ``database``. Duplicate names will be elided.
            mask (Union[dict, ~google.cloud.firestore_v1beta1.types.DocumentMask]): The fields to return. If not set, returns all fields.

                If a document has a field that is not present in this mask, that field will
                not be returned in the response.

                If a dict is provided, it must be of the same form as the protobuf
                message :class:`~google.cloud.firestore_v1beta1.types.DocumentMask`
            transaction (bytes): Reads documents in a transaction.
            new_transaction (Union[dict, ~google.cloud.firestore_v1beta1.types.TransactionOptions]): Starts a new transaction and reads the documents.
                Defaults to a read-only transaction.
                The new transaction ID will be returned as the first response in the
                stream.

                If a dict is provided, it must be of the same form as the protobuf
                message :class:`~google.cloud.firestore_v1beta1.types.TransactionOptions`
            read_time (Union[dict, ~google.cloud.firestore_v1beta1.types.Timestamp]): Reads documents as they were at the given time.
                This may not be older than 60 seconds.

                If a dict is provided, it must be of the same form as the protobuf
                message :class:`~google.cloud.firestore_v1beta1.types.Timestamp`
            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:
            Iterable[~google.cloud.firestore_v1beta1.types.BatchGetDocumentsResponse].

        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 batch_get_documents(
        self,
        database,
        documents,
        mask=None,
        transaction=None,
        new_transaction=None,
        read_time=None,
        retry=google.api_core.gapic_v1.method.DEFAULT,
        timeout=google.api_core.gapic_v1.method.DEFAULT,
        metadata=None,
    ):
        """
        Gets multiple documents.

        Documents returned by this method are not guaranteed to be returned in the
        same order that they were requested.

        Example:
            >>> from google.cloud import firestore_v1beta1
            >>>
            >>> client = firestore_v1beta1.FirestoreClient()
            >>>
            >>> database = client.database_root_path('[PROJECT]', '[DATABASE]')
            >>>
            >>> # TODO: Initialize `documents`:
            >>> documents = []
            >>>
            >>> for element in client.batch_get_documents(database, documents):
            ...     # process element
            ...     pass

        Args:
            database (str): The database name. In the format:
                ``projects/{project_id}/databases/{database_id}``.
            documents (list[str]): The names of the documents to retrieve. In the format:
                ``projects/{project_id}/databases/{database_id}/documents/{document_path}``.
                The request will fail if any of the document is not a child resource of
                the given ``database``. Duplicate names will be elided.
            mask (Union[dict, ~google.cloud.firestore_v1beta1.types.DocumentMask]): The fields to return. If not set, returns all fields.

                If a document has a field that is not present in this mask, that field will
                not be returned in the response.

                If a dict is provided, it must be of the same form as the protobuf
                message :class:`~google.cloud.firestore_v1beta1.types.DocumentMask`
            transaction (bytes): Reads documents in a transaction.
            new_transaction (Union[dict, ~google.cloud.firestore_v1beta1.types.TransactionOptions]): Starts a new transaction and reads the documents.
                Defaults to a read-only transaction.
                The new transaction ID will be returned as the first response in the
                stream.

                If a dict is provided, it must be of the same form as the protobuf
                message :class:`~google.cloud.firestore_v1beta1.types.TransactionOptions`
            read_time (Union[dict, ~google.cloud.firestore_v1beta1.types.Timestamp]): Reads documents as they were at the given time.
                This may not be older than 60 seconds.

                If a dict is provided, it must be of the same form as the protobuf
                message :class:`~google.cloud.firestore_v1beta1.types.Timestamp`
            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:
            Iterable[~google.cloud.firestore_v1beta1.types.BatchGetDocumentsResponse].

        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 "batch_get_documents" not in self._inner_api_calls:
            self._inner_api_calls[
                "batch_get_documents"
            ] = google.api_core.gapic_v1.method.wrap_method(
                self.transport.batch_get_documents,
                default_retry=self._method_configs["BatchGetDocuments"].retry,
                default_timeout=self._method_configs["BatchGetDocuments"].timeout,
                client_info=self._client_info,
            )

        # Sanity check: We have some fields which are mutually exclusive;
        # raise ValueError if more than one is sent.
        google.api_core.protobuf_helpers.check_oneof(
            transaction=transaction,
            new_transaction=new_transaction,
            read_time=read_time,
        )

        request = firestore_pb2.BatchGetDocumentsRequest(
            database=database,
            documents=documents,
            mask=mask,
            transaction=transaction,
            new_transaction=new_transaction,
            read_time=read_time,
        )
        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["batch_get_documents"](
            request, retry=retry, timeout=timeout, metadata=metadata
        )