CRUD Operations with Azure Blob Storage in an Azure Function – Update & Deletion

In the preceeding parts of this series, we have delved into how to Create and Retrieve blobs using Azure Web Functions. In this part, we will look into how delete the blobs from Azure Blob Storage.

Wait a minute !! Did that we mean we skip Update ? Not really, we will have a word about it before we start with Deletion.

Update Blobs

The reason I thought Update Blobs doesn’t require its own blog post was it is quite different from what we learned for Creation (for starters, without delving too much into details). In fact, there is no difference at all.

Consider the Block Blobs – most likely, these are single files whose updation implies replacing them with a updated version. This could be an image file or an media file. This is no different from creating a new file.

You could overwrite an existing blob using the same code which learned in the previous post.

using (var stream = data.OpenReadStream())
{
    var blob = blobContainer.GetBlockBlobReference(key);
    await blob.UploadFromStreamAsync(stream);
}

With Append Blob, as the name suggests, the action is more of an “append to end of blob” scenario. This is whatthe Append blob is designed for. You could do exactly that using your learnings in the previous blog.

Deletion

Now that we have briefly spoken about the Updatation process, let us move ahead with the Deletion.

How do one delete a blob ? Well the answer is pretty simple, and is almost the same for Block and Append Blobs.

[FunctionName("DeleteFileBlockBlob")]
public static async Task<IActionResult> DeleteFileBlockBlob(
    [HttpTrigger(AuthorizationLevel.Anonymous, "post", Route = null)] HttpRequest req,
    [Blob("todos")] CloudBlobContainer blobContainer,
    ILogger log
    )
{
    string key = req.Query["key"];

    var blob = blobContainer.GetBlockBlobReference(key);
    var result = await blob.DeleteIfExistsAsync();

    return new OkObjectResult($"Item Deletion {(result ? "Success" : "Failed")}");
}

As you notice in the code above, all it takes is to get a reference to the blob using the now familiar CloudBlobContainer.GetBlockBlobReference and use the CloudBlockBlob.DeleteIfExistsAsync to delete it.

With the Append Blob, obviously, one needs to get reference to the Append Blob, instead of Block Blob, but the code feels no different. Take a look at the example below.

[FunctionName("DeleteFileAppendBlob")]
public static async Task<IActionResult> DeleteFileAppendBlob(
[HttpTrigger(AuthorizationLevel.Anonymous, "post", Route = null)] HttpRequest req,
[Blob("sample")] CloudBlobContainer blobContainer,
ILogger log
)
{
    string key = req.Query["key"];

    var blob = blobContainer.GetAppendBlobReference(key);
    var result = await blob.DeleteIfExistsAsync();

    return new OkObjectResult($"Item Deletion {(result ? "Success" : "Failed")}");
}

That’s hardly any different.

So we have so far, looked into basics of CRUD operations into Azure Table Storage and Azure Blob Storage. We will continue our exploration of Azure Storage options and also take time to delve deeper in the configurations/security options in the upcoming blobs.

Until then, keep coding !!! As always, all code discussed here are available in my Github. For complete series on Azure Storage, refer here

CRUD Operations with Azure Blob Storage in an Azure Function – Read

In the previous post, we examined how we could add an item to the Azure blob.

In this part, we will use an Azure function to download the file store in Azure Blob Storage.

Block Blob

Let us begin with Block Blobs.

[FunctionName("DownloadBlockBlob")]
public static async Task<IActionResult> DownloadBlockBlob(
    [HttpTrigger(AuthorizationLevel.Anonymous,"get",Route =null)] HttpRequest req,
    [Blob("todos")] CloudBlobContainer blobContainer,
    ILogger log)
{
    var key = req.Query["key"];

    var stream = new MemoryStream();
    var blob = await blobContainer.GetBlobReferenceFromServerAsync(key);
    await blob.DownloadToStreamAsync(stream);
    stream.Position = 0;
    return new FileStreamResult(stream, "application/octet-stream") { FileDownloadName = key };
}

This turns out to be pretty straightforward, isn’t it. The CloudBlobContainer.GetBlobReferenceFromServerAsync gets the reference to the blob we are interested in using the blob name, in this case, passed on as a query parameter. We could then use the CloudBlob.DownloadToStreamAsync method to download the contents of the blob to a stream, which could be later pass back using the FileStreamResult.

One obvious question would be why use a azure function in the above case, when there is no authentication. One could directly use a Http Get Request. Partially, that is true, however, do not forget this is only an example and most often than note, authentication would not be anonymous and there could be other things that you would like your azure function to during the download, like a log or updating/fetching another document.

Of course, you could simplify things using input bindings. For example, the above code could be rewritten using binding as the following.

[FunctionName("DownloadBlockBlobUsingBinding")]
public static async Task<IActionResult> DownloadBlockBlobUsingBinding(
[HttpTrigger(AuthorizationLevel.Anonymous, "get", Route = "DownloadBlockBlobUsingBinding/{fileName}")] HttpRequest req,
[Blob("todos/{fileName}",FileAccess.Read)] Stream blob,
string fileName,
ILogger log)
{
    var memoryStream = new MemoryStream();
    await blob.CopyToAsync(memoryStream);
    memoryStream.Position = 0;
    return new FileStreamResult(memoryStream, "application/octet-stream") { FileDownloadName = fileName };
}

Append Blob

To download a file from an Append Blob is no different from what we have seen with Block Blob.

[FunctionName("DownloadAppendBlob")]
public static async Task<IActionResult> DownloadAppendBlob(
[HttpTrigger(AuthorizationLevel.Anonymous, "get", Route = null)] HttpRequest req,
[Blob("sample")] CloudBlobContainer blobContainer,
ILogger log)
{

    var key = req.Query["key"];

    var stream = new MemoryStream();
    var blob = blobContainer.GetAppendBlobReference(key);
    await blob.DownloadToStreamAsync(stream);
    stream.Position = 0;
    return new FileStreamResult(stream, "text/plain") { FileDownloadName = key };
}


The only point of importance while learning would be to remember that Append Blobs are not supported by the Storage emulator. For rest of the code look quite similar to the Block blob, sole difference being we use a different method to get reference to the blob – CloudContainer.GetAppendBlobReference.

As mentioned in the earlier post, we will address the Page blob separately. But for now, go ahead and play around with the Block Blob and Append Blob. You could access the source code explained in this code in my Github