samples: add metageneration-match preconditions to samples (#975)

* samples: add metageneration-match preconditions to samples

* update optional block wording and flow

Author: cojenco

packages/google-cloud-storage/samples/snippets/storage_release_event_based_hold.py

@@ -29,9 +29,16 @@ def release_event_based_hold(bucket_name, blob_name):
     storage_client = storage.Client()
     bucket = storage_client.bucket(bucket_name)
     blob = bucket.blob(blob_name)
+    metageneration_match_precondition = None
+
+    # Optional: set a metageneration-match precondition to avoid potential race
+    # conditions and data corruptions. The request to patch is aborted if the
+    # object's metageneration does not match your precondition.
+    blob.reload()  # Fetch blob metadata to use in metageneration_match_precondition.
+    metageneration_match_precondition = blob.metageneration
 
     blob.event_based_hold = False
-    blob.patch()
+    blob.patch(if_metageneration_match=metageneration_match_precondition)
 
     print(f"Event based hold was released for {blob_name}")
 

packages/google-cloud-storage/samples/snippets/storage_release_temporary_hold.py

@@ -29,9 +29,16 @@ def release_temporary_hold(bucket_name, blob_name):
     storage_client = storage.Client()
     bucket = storage_client.bucket(bucket_name)
     blob = bucket.blob(blob_name)
+    metageneration_match_precondition = None
+
+    # Optional: set a metageneration-match precondition to avoid potential race
+    # conditions and data corruptions. The request to patch is aborted if the
+    # object's metageneration does not match your precondition.
+    blob.reload()  # Fetch blob metadata to use in metageneration_match_precondition.
+    metageneration_match_precondition = blob.metageneration
 
     blob.temporary_hold = False
-    blob.patch()
+    blob.patch(if_metageneration_match=metageneration_match_precondition)
 
     print("Temporary hold was release for #{blob_name}")
 

packages/google-cloud-storage/samples/snippets/storage_set_event_based_hold.py

@@ -28,9 +28,16 @@ def set_event_based_hold(bucket_name, blob_name):
     storage_client = storage.Client()
     bucket = storage_client.bucket(bucket_name)
     blob = bucket.blob(blob_name)
+    metageneration_match_precondition = None
+
+    # Optional: set a metageneration-match precondition to avoid potential race
+    # conditions and data corruptions. The request to patch is aborted if the
+    # object's metageneration does not match your precondition.
+    blob.reload()  # Fetch blob metadata to use in metageneration_match_precondition.
+    metageneration_match_precondition = blob.metageneration
 
     blob.event_based_hold = True
-    blob.patch()
+    blob.patch(if_metageneration_match=metageneration_match_precondition)
 
     print(f"Event based hold was set for {blob_name}")
 

packages/google-cloud-storage/samples/snippets/storage_set_metadata.py

@@ -28,9 +28,16 @@ def set_blob_metadata(bucket_name, blob_name):
     storage_client = storage.Client()
     bucket = storage_client.bucket(bucket_name)
     blob = bucket.get_blob(blob_name)
+    metageneration_match_precondition = None
+
+    # Optional: set a metageneration-match precondition to avoid potential race
+    # conditions and data corruptions. The request to patch is aborted if the
+    # object's metageneration does not match your precondition.
+    metageneration_match_precondition = blob.metageneration
+
     metadata = {'color': 'Red', 'name': 'Test'}
     blob.metadata = metadata
-    blob.patch()
+    blob.patch(if_metageneration_match=metageneration_match_precondition)
 
     print(f"The metadata for the blob {blob.name} is {blob.metadata}")
 

packages/google-cloud-storage/samples/snippets/storage_set_temporary_hold.py

@@ -28,9 +28,16 @@ def set_temporary_hold(bucket_name, blob_name):
     storage_client = storage.Client()
     bucket = storage_client.bucket(bucket_name)
     blob = bucket.blob(blob_name)
+    metageneration_match_precondition = None
+
+    # Optional: set a metageneration-match precondition to avoid potential race
+    # conditions and data corruptions. The request to patch is aborted if the
+    # object's metageneration does not match your precondition.
+    blob.reload()  # Fetch blob metadata to use in metageneration_match_precondition.
+    metageneration_match_precondition = blob.metageneration
 
     blob.temporary_hold = True
-    blob.patch()
+    blob.patch(if_metageneration_match=metageneration_match_precondition)
 
     print("Temporary hold was set for #{blob_name}")