Azure Function Blob Trigger CloudBlockBlob binding

Question

I have the following Azure function triggered when a file is uploaded to Blob Storage

[FunctionName("ImageAnalysis")]
    public static async void Run(
        [BlobTrigger("imageanalysis/{name}", Connection = "AzureWebJobsStorage")] Stream myBlob, 
        string name, 
        TraceWriter log)
    {
        log.Info($"C# Blob trigger function Processed blob\n Name:{name} \n Size: {myBlob.Length} Bytes");
    }

I want to process the Blob that has been uploaded so ideally I would like it as a CloudBlockBlob instead of a Stream. Then I can just do some work and then delete the blob.

myBlob.DeleteIfExists()

Is there an easy way to cast or convert my Stream to CloudBlockBlob or do I need to use input/output bindings or something else?

Looking through the docs I see examples which use CloudBlockBlob but I can't seem to get it to work so think I am missing something?

Please expand on "I can't seem to get it to work". CloudBlockBlob is supported. — Mikhail Shilkov
– Mikhail Shilkov, Commented Mar 20, 2018 at 13:34

McGuireV10 · Accepted Answer · 2018-03-29 12:31:39Z

8

Use this syntax for the binding. The trick is specifying FileAccess.ReadWrite in the attribute. The docs rather confusingly refer to this as "inout" for some reason.

[Blob("imageanalysis/{name}", FileAccess.ReadWrite, Connection = "AzureWebJobsStorage")] CloudBlockBlob blob, string name

edited Mar 29, 2018 at 12:31

answered Mar 20, 2018 at 13:35

McGuireV10

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5 Comments

Simon Foster Over a year ago

I must be doing something wrong I keep getting Microsoft.Azure.WebJobs.Host: Error indexing method 'ImageAnalysis.Run'. Microsoft.Azure.WebJobs.Host: Can't bind Blob to type 'Microsoft.WindowsAzure.Storage.Blob.CloudBlockBlob'.

Simon Foster Over a year ago

Ignore me I had the wrong version of Microsoft.WindowsAzure.Storage.Blob rolling back to 7.2.1 fixed it

McGuireV10 Over a year ago

Glad you got it going. Some of the Azure namespaces and assemblies can get very confusing (particularly around the new vs. old queue APIs).

Gabriel Cerutti Over a year ago

So, the solution is rolling back the library to an old version? I don't think this is a suitable fix.

McGuireV10 Over a year ago

Since you don't control the deployment platform itself, working with Azure Functions is often more "do what works" than what might seem ideal. (And frankly, due to fiascoes like hard dependencies on old JSON.NET packages and other headaches, we've given up on them for the time being.)

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