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AccessCondition.IfModifiedSince Method

Updated: April 24, 2013

[This topic is part of the Windows Azure Storage Client Library 1.7, which has been deprecated. The current recommended version is Storage Client Library 3.0.]

Returns an access condition such that an operation will be performed only if the resource has been modified since the specified time.

Namespace: Microsoft.WindowsAzure.StorageClient
Assembly: Microsoft.WindowsAzure.StorageClient (in Microsoft.WindowsAzure.StorageClient.dll)


public static AccessCondition IfModifiedSince (
	DateTime lastModifiedUtc



The last-modified time for the resource, expressed as a UTC value.

Return Value

A structure specifying the If-Modified-Since condition.

The following code example checks an access condition on the source blob and copies the blob if the condition is met.

static void CopyIfModifiedSince(Uri blobEndpoint, string accountName, string accountKey)
    //Create service client for credentialed access to the Blob service.
    CloudBlobClient blobClient = new CloudBlobClient(blobEndpoint, new StorageCredentialsAccountAndKey(accountName, accountKey));

    //Get a reference to the source blob.
    CloudBlob sourceBlob = blobClient.GetBlobReference("mycontainer/myblob.txt");

    //Get a reference to the destination blob.
    CloudBlob destBlob = blobClient.GetBlobReference("mycontainer/copy-if-modified-since.txt");
    BlobRequestOptions options = new BlobRequestOptions();
    DateTime dt = new DateTime(2010, 9, 1, 0, 0, 0, DateTimeKind.Utc);

        //Copy the source blob to the destination blob if the source blob has been modified since 9/1/2010.
        options.CopySourceAccessCondition = AccessCondition.IfModifiedSince(dt.ToUniversalTime());
        destBlob.CopyFromBlob(sourceBlob, options);
    catch (StorageClientException e)
        if (e.StatusCode == HttpStatusCode.PreconditionFailed)
            Console.WriteLine("Access condition not met - blob " + sourceBlob.Uri + " has not been modified since " + dt.ToUniversalTime());
            Console.WriteLine("Error code: " + e.ErrorCode);

Setting this access condition modifies the request to include the HTTP If-Modified-Since conditional header.

If this access condition is set, the operation is performed only if the resource has been modified since the specified time.

See Specifying Conditional Headers for Blob Service Operations for more information.

Any public static (Shared in Visual Basic) members of this type are thread safe. Any instance members are not guaranteed to be thread safe.

Development Platforms

Windows Vista, Windows 7 and Windows Server 2008

Target Platforms

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