Blob storage has the concept of containers (which can be thought of as directories) and those containers can contain BLOB’s. Containers cannot contain containers and hence differ from a file system in structure.

Containers can be private or allow anonymous read access to BLOBs only or allow anonymous read access for containers and BLOBs.

In the Azure Portal, if you haven’t already got one set up, create a storage account then create a Blob service. Next create a container, mine’s named test. Next, upload a file, I’ve uploaded Hello World.txt which as you imagine simply has the line Hello World within it.

When you create a Blob service you’re assigned an endpoint name, along the lines of https://<storage account>.blob.core.winodws.net/

When we add containers, these get the URL https://<storage account>.blob.core.windows.net/<container name> and files get the URL https://<storage account>.blob.core.windows.net/<container name>/<file name>

A comprehensive document on using .NET to interact with the Blob storage can be found at Get started with Azure Blob storage using .NET.

Reading a Blob

Here’s some code to read our uploaded Hello World.txt file

Firstly we need to use NuGet to add package WindowsAzure.Storage and Microsoft.WindowsAzure.ConfigurationManager.

using Microsoft.Azure;
using Microsoft.WindowsAzure.Storage;

private static void ReadBlob()
{
   var storageAccount = CloudStorageAccount.Parse(
      CloudConfigurationManager.GetSetting(
         "StorageConnectionString"));

   var blobClient = storageAccount.CreateCloudBlobClient();
   var container = blobClient.GetContainerReference("test");
   var blob = container.GetBlockBlobReference("Hello World.txt");
   var contents = blob.DownloadText();

   Console.WriteLine(contents);
}

In the example our file is a text file, but we can also access the blob as a stream using DownloadToStream (plus there’s a whole bunch of other methods for accessing the blobs).

Writing a Blob

We can write blobs pretty easily also

public static void WriteBlob()
{
   var storageAccount = CloudStorageAccount.Parse(
      CloudConfigurationManager.GetSetting(
         "StorageConnectionString"));

   var blobClient = storageAccount.CreateCloudBlobClient();

   var container = blobClient.GetContainerReference("test");

   var blob = container.GetBlockBlobReference("new.txt");
   blob.UploadFromFile("new.txt");
}

In this example, as you’ll see, we still do the standard, connect to cloud via the blob client, get a reference to the container we want to interact with, but next we get a blob to a file (in this case new.txt didn’t exist) and then upload or write from a stream to blob storage. If “new.txt” does exist in the blob storage it’ll simply be overwritten.

Deleting a Blob

We’ve looked at Creation/Update of blobs and Retrieval or them so let’s complete CRUD operations on blobs with delete

public static void DeleteBlob()
{
   var storageAccount = CloudStorageAccount.Parse(
      CloudConfigurationManager.GetSetting(
         "StorageConnectionString"));

   var blobClient = storageAccount.CreateCloudBlobClient();

   var container = blobClient.GetContainerReference("test");

   var blob = container.GetBlockBlobReference("new.txt");
   blob.DeleteIfExists();
}

References

Along with the standard CRUD type operations we can carry out actions on containers, list blobs etc.

See Get started with Azure Blob storage using .NET for more information.

The Blob Service REST API lists the REST API’s if you’d prefer to bypass the Microsoft libraries for accessing the Blobs (or need to implement in a different language).