google-cloud-python: Unable to set blob metadata

I think this is a duplicate of #754. The use of metadata is a bit ambiguous as metadata refers to both the metadata of an object (such as Cache-Control) and the metadata property, meant for custom metadata.

Anyway, to the issue. Any update? The problem with patch is that the object is online briefly with wrong metadata, or less briefly in case of a connection failure between two requests. And, it increases metageneration.

>>> text = bucket.blob('file.txt')
>>> text.cache_control = 'no-cache'
>>> text.upload_from_string('text')
>>> text.reload()
>>> text.cache_control
>>> text.metageneration
1
>>> text.cache_control = 'no-cache'
>>> text.patch()
>>> text.reload()
>>> text.cache_control
u'no-cache'
>>> text.metageneration
2

You can work around this bug by creating a completely new dictionary, assigning it to blob.metadata, and doing blob.patch():

newdict={}
for x in blob.metadata:
    newdict[x] = blob.metadata[x]
    newdict['mynewproperty'] = 'awesome'
blob.metadata=newdict
blob.patch()

Your blob will now have the {‘mynewproperty’:‘awesome’} metadata property in its stored metadata list on GCS.

I had some trouble getting this to work because the metadata was always None (even though I manually added values via the Storage UI). Later I realized I was using bucket.blob("name") rather than bucket.get_blob("name") so the metadata hadn’t been loaded. Might help someone else.

I’ve updated a previous patch, hack perhaps, which makes it work. It’s not tested extensively.

--- a/blob.py
+++ b/blob.py
@@ -494,6 +494,11 @@
 
         # Configure the upload request parameters.
         request = Request(upload_url, 'POST', headers)
+
+        if self._properties:
+            headers['content-type'] = 'application/json'
+            request.body = json.dumps(self._properties)
+
         upload.configure_request(upload_config, request, url_builder)
 
         # Configure final URL

The file google/cloud/storage/blob.py is located in your Python site-packages directory.

>>> text = bucket.blob('file.txt')
>>> text.cache_control = 'no-cache'
>>> text.metadata = {'custom': 'metadata'}
>>> text.upload_from_string('text')
>>> text.reload()
>>> text.cache_control
u'no-cache'
>>> text.metadata
{u'custom': u'metadata'}
>>> text.metageneration
1
>>> text.download_as_string()
'text'

blob.upload_from_file()
blob.metadata = {'luke': 'skywalker'}
blob.patch()

worked for me. I was able to upload a file and apply the meta data after the file upload.

@Prabakaran1410 You don’t need to call patch on the blob after upload: since PR #3362, all properties assigned to the blob before upload are passed through.

@saxenanurag I’m in the middle of reviewing how we are using the ex-apitools code (now in gcloud.streaming), and can see how we should be able to send the patched metadata along with the upload request.

Setting the metadata locally does not cause the instance to make the API call to patch it on the server, and we don’t send metadata along with the upload_from_file() call. You need to add a call to blob.patch() to persist the changes to blob.metadata.