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Rob Church
Rob Church

Reputation: 6943

How do I upload to Azure Blob storage without overwriting?

Calling UploadFromStream overwrites files by default - how can I make sure I only upload a blob if it isn't already in the container?

CloudBlockBlob blockBlob = container.GetBlockBlobReference(blobName);
blockBlob.UploadFromStream(stream)

Upvotes: 26

Views: 9979

Answers (3)

Rob Church
Rob Church

Reputation: 6943

Add an access condition to the code so that it checks against the ETag property of the blob - wildcards are allowed, so we want to only allow the upload if no blobs with this name have any etag (which is a roundabout way of saying, does this blob name exist).

You get a StorageException as detailed below.

    CloudBlockBlob blockBlob = container.GetBlockBlobReference(blobName);
    try {
        blockBlob.UploadFromStream(stream, accessCondition: AccessCondition.GenerateIfNoneMatchCondition("*"));
    } catch (StorageException ex) {
        if (ex.RequestInformation.HttpStatusCode == (int)System.Net.HttpStatusCode.Conflict) {
            // Handle duplicate blob condition
        }
        throw;
    }

Upvotes: 24

Matt Jacobi
Matt Jacobi

Reputation: 864

Azure now has an access condition that will only add, not overwrite: AccessCondition.GenerateIfNotExistsCondition()

Definition:

Constructs an access condition such that an operation will be performed only if the resource does not exist.

Example:

var accessCondition = AccessCondition.GenerateIfNotExistsCondition();
blockBlob.UploadFromStream(stream, accessCondition);

Upvotes: 11

Strydom
Strydom

Reputation: 970

The answer provided by Rob Church seems ok. Checking strings for errors isn't best practice and be improved with:

        CloudBlockBlob blockBlob = container.GetBlockBlobReference(blobName);
        try
        {
            blockBlob.UploadFromStream(stream, accessCondition: AccessCondition.GenerateIfNoneMatchCondition("*"));
        }
        catch (StorageException ex)
        {
            if (ex.RequestInformation.HttpStatusCode == (int)System.Net.HttpStatusCode.Conflict)
            {
                // Handle duplicate blob condition
            }
            throw;
        }

Upvotes: 3

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