docs: add clarification to batch module (#1045)

* docs: add clarification to batch module

* clarify constraints with batch

* update docs

google/cloud/storage/batch.py

@@ -13,7 +13,21 @@
 # limitations under the License.
 """Batch updates / deletes of storage buckets / blobs.
 
-See https://cloud.google.com/storage/docs/json_api/v1/how-tos/batch
+A batch request is a single standard HTTP request containing multiple Cloud Storage JSON API calls.
+Within this main HTTP request, there are multiple parts which each contain a nested HTTP request.
+The body of each part is itself a complete HTTP request, with its own verb, URL, headers, and body.
+
+Note that Cloud Storage does not support batch operations for uploading or downloading.
+Additionally, the current batch design does not support library methods whose return values
+depend on the response payload. See more details in the [Sending Batch Requests official guide](https://cloud.google.com/storage/docs/batch).
+
+Examples of situations when you might want to use the Batch module:
+``blob.patch()``
+``blob.update()``
+``blob.delete()``
+``bucket.delete_blob()``
+``bucket.patch()``
+``bucket.update()``
 """
 from email.encoders import encode_noop
 from email.generator import Generator
@@ -131,6 +145,12 @@ def content(self):
 class Batch(Connection):
     """Proxy an underlying connection, batching up change operations.
 
+    .. warning::
+
+        Cloud Storage does not support batch operations for uploading or downloading.
+        Additionally, the current batch design does not support library methods whose
+        return values depend on the response payload.
+
     :type client: :class:`google.cloud.storage.client.Client`
     :param client: The client to use for making connections.
 

google/cloud/storage/blob.py

@@ -3450,6 +3450,10 @@ def rewrite(
         If :attr:`user_project` is set on the bucket, bills the API request
         to that project.
 
+        .. note::
+
+           ``rewrite`` is not supported in a ``Batch`` context.
+
         :type source: :class:`Blob`
         :param source: blob whose contents will be rewritten into this blob.
 

google/cloud/storage/bucket.py

@@ -1482,7 +1482,8 @@ def delete(
         If ``force=True`` and the bucket contains more than 256 objects / blobs
         this will cowardly refuse to delete the objects (or the bucket). This
         is to prevent accidental bucket deletion and to prevent extremely long
-        runtime of this method.
+        runtime of this method. Also note that ``force=True`` is not supported
+        in a ``Batch`` context.
 
         If :attr:`user_project` is set, bills the API request to that project.
 
@@ -1675,6 +1676,7 @@ def delete_blobs(
                          Called once for each blob raising
                          :class:`~google.cloud.exceptions.NotFound`;
                          otherwise, the exception is propagated.
+                         Note that ``on_error`` is not supported in a ``Batch`` context.
 
         :type client: :class:`~google.cloud.storage.client.Client`
         :param client: (Optional) The client to use.  If not passed, falls back
@@ -1801,6 +1803,8 @@ def copy_blob(
         :param preserve_acl: DEPRECATED. This argument is not functional!
                              (Optional) Copies ACL from old blob to new blob.
                              Default: True.
+                             Note that ``preserve_acl`` is not supported in a
+                             ``Batch`` context.
 
         :type source_generation: long
         :param source_generation: (Optional) The generation of the blob to be
@@ -1932,8 +1936,11 @@ def rename_blob(
           old blob.  This means that with very large objects renaming
           could be a very (temporarily) costly or a very slow operation.
           If you need more control over the copy and deletion, instead
-          use `google.cloud.storage.blob.Blob.copy_to` and
-          `google.cloud.storage.blob.Blob.delete` directly.
+          use ``google.cloud.storage.blob.Blob.copy_to`` and
+          ``google.cloud.storage.blob.Blob.delete`` directly.
+
+          Also note that this method is not fully supported in a
+          ``Batch`` context.
 
         :type blob: :class:`google.cloud.storage.blob.Blob`
         :param blob: The blob to be renamed.

samples/snippets/storage_batch_request.py

@@ -28,7 +28,14 @@
 
 
 def batch_request(bucket_name, prefix=None):
-    """Use a batch request to patch a list of objects with the given prefix in a bucket."""
+    """
+    Use a batch request to patch a list of objects with the given prefix in a bucket.
+
+    Note that Cloud Storage does not support batch operations for uploading or downloading.
+    Additionally, the current batch design does not support library methods whose return values
+    depend on the response payload.
+    See https://cloud.google.com/python/docs/reference/storage/latest/google.cloud.storage.batch
+    """
     # The ID of your GCS bucket
     # bucket_name = "my-bucket"
     # The prefix of the object paths