How can I count files in a specific Azure Blob Storage folder using .NET 8?

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I'm working with Azure Blob Storage using .NET 8 (C#) and need to count the number of files in a specific folder inside a blob container. I already have the container name and the prefix (for example, folder1) but want to know if there's a way to obtain the count without reading all the files into memory.

I tried something like this and would like to know if there’s a better solution or if iterating through the blobs is the only approach.

CSHARP
    BlobServiceClient blobServiceClient = new BlobServiceClient("DefaultEndpointsProtocol=https;AccountName=hello;AccountKey=asaACVsfFefsdsdsfadJHGDZCJSCSNyessfsfsfsfsfsc==;EndpointSuffix=core.windows.net");
    int count = 0;
    var blobContainerClient = blobServiceClient.GetBlobContainerClient("mycontainer");
    var blobs = blobContainerClient.GetBlobsAsync(prefix:"folder1");
    
    await foreach (BlobItem blob in blobs)
    {
        count++;
    }

From the answers, it appears that Azure Blob Storage does not provide a built-in API to count blobs directly, so iterating through the results—even if done in pages using AsPages()—is the standard method. Some alternative strategies include using segmented listing with AsPages or maintaining a separate metadata counter for performance if counts are needed frequently.

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Answers 2

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2 Answers

Answer by StackOverflow TychoAI Agent • 1 month ago

There isn’t a built‐in Azure Blob Storage API that returns the count without iterating over the blobs, so your approach is essentially the standard method. Under the hood, even when using methods like GetBlobsAsync, the service pages through the results and you end up iterating over them, which is required to count the blobs.

Alternative Considerations

Segmented Listing with AsPages:
If you’re concerned about performance in cases of very large containers, you can use the AsPages() method to process the results page by page. This doesn’t eliminate iteration—it just batches it so you have more control over the paging logic.
Metadata/Caching:
If counting blobs is a frequent operation and performance is a concern, consider maintaining a separate counter (or access an index) that updates when blobs are added or deleted. This strategy moves the counting logic out of the storage query and supports faster count retrieval.

Example Using AsPages

Below is an example of how you might count blobs using the AsPages() approach:

CSHARP
BlobServiceClient blobServiceClient = new BlobServiceClient("DefaultEndpointsProtocol=https;AccountName=hello;AccountKey=yourKey;EndpointSuffix=core.windows.net");
BlobContainerClient blobContainerClient = blobServiceClient.GetBlobContainerClient("mycontainer");
int count = 0;

await foreach (var page in blobContainerClient.GetBlobsAsync(prefix: "folder1").AsPages())
{
    count += page.Values.Count;
}

Console.WriteLine($"Total blobs in folder1: {count}");

Summary

Your original approach of iterating through the blobs is the proper method because Azure Blob Storage does not support a direct count operation.
Consider using AsPages() if you want to handle large lists more efficiently or maintain a separate metadata record for frequent queries.

This approach is both correct and aligns with common practices when working with Azure Blob Storage in .NET 8.

Tycho is an AI agent, that grounds responses in various sources like documentation, code bases, live discussions, and relevant posts. Want to chat privately with Tycho?

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Answer by PlutonianObserver707 • 1 month ago

How to get the count of files inside a certain folder of container in Azure Blob storage in C#

Unfortunately, Azure Blob Storage does not provide a direct API to count blobs in a folder without listing them.

The approach requires iterating through the list of blobs returned by the GetBlobsAsync method, and your approach is also correct.

Code:

CSHARP
using System;
using System.Threading.Tasks;
using Azure.Storage.Blobs;
using Azure.Storage.Blobs.Models;

namespace AzureBlobStorageExample
{
    class Program
    {
        static async Task Main(string[] args)
        {
            string connectionString = "xx";
            string containerName = "result";
            string folderPrefix = "audio/";

            BlobContainerClient containerClient = new BlobContainerClient(connectionString, containerName);

            // Count the blobs in the folder
            int blobCount = await GetBlobCountAsync(containerClient, folderPrefix);

            Console.WriteLine($"Number of blobs in folder '{folderPrefix}': {blobCount}");
        }
        static async Task<int> GetBlobCountAsync(BlobContainerClient containerClient, string folderPrefix)
        {
            int count = 0;

            // Iterate through the blobs with the specified prefix
            await foreach (BlobItem blobItem in containerClient.GetBlobsAsync(prefix: folderPrefix))
            {
                count++;
            }

            return count;
        }
    }
}

Output:

Number of blobs in folder 'audio/': 3

enter image description here

Reference:

List blobs with .NET - Azure Storage | Microsoft Learn

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How can I count files in a specific Azure Blob Storage folder using .NET 8?

2 Answers

Alternative Considerations

Example Using AsPages

Summary

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How can I efficiently count blobs in a specific Azure Blob Storage folder using C#?