Can PutBlock be used to append to an existing BlockBlob in Azure

问题

As per the title, I have a program whereby I'm trying to add to an existing BlobkBlob using the PutBlock method:

    private static void UploadNewText(string text)
    {
        string fileName = "test4.txt";
        string containerString = "mycontainer";

        CloudStorageAccount storage = CloudStorageAccount.Parse(connection);
        CloudBlobClient client = storage.CreateCloudBlobClient();
        CloudBlobContainer container = client.GetContainerReference(containerString);
        CloudBlockBlob blob = container.GetBlockBlobReference(fileName);

        using (MemoryStream stream = new MemoryStream())
        using (StreamWriter sw = new StreamWriter(stream))
        {
            sw.Write(text);
            sw.Flush();
            stream.Position = 0;

            string blockId = Convert.ToBase64String(
                ASCIIEncoding.ASCII.GetBytes("0000005"));

            Console.WriteLine(blockId);

            blob.PutBlock(blockId, stream, null);
            blob.PutBlockList(new string[] { blockId });
        }
    }

As I understand it, providing the BlockId increases (or at least differs), and is a consistent size, this should work; however, when I run it a second time for the same file (regardless of whether or not I increase the Block ID) it just overwrites the existing file with the new text.

I realise there are other options for appending to a blob (such as AppendBlob), but I'm curious if PutBlock, specifically can do this. Is what I am trying to do possible and, if so, what am I doing wrong?

回答1:

Can PutBlock be used to append to an existing BlockBlob in Azure

Yes, it can. However in order to do that, you will need to work that in a little bit different way.

What you will need to do is:

First get the previously committed block list. The method you want to use is DownloadBlockList.
Upload new block. Note down its block id.
Append this block id to the list of block ids you downloaded in step #1.
Call put block list with this new list.

来源：https://stackoverflow.com/questions/46368954/can-putblock-be-used-to-append-to-an-existing-blockblob-in-azure

标签

azure

azure-storage-blobs