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使用yield延迟Azure blob存储调用-c#

yield ienumerable azure-storage-blobs azure c#

1

Rob · 技术社区 · 7 年前

internal async Task<IEnumerable<BlobItem>> GetFiles(CloudBlobContainer container, string directoryName, bool recursive)
{
    var results = new List<BlobItem>();
    BlobContinuationToken continuationToken = null;

    do
    {
        var response = await container.GetDirectoryReference(directoryName).ListBlobsSegmentedAsync(false, BlobListingDetails.None, 100, continuationToken, null, null);

        continuationToken = response.ContinuationToken;
        foreach (var item in response.Results)
        {
            if (item.GetType() != typeof(CloudBlobDirectory))
                results.Add(new BlobItem(item));
            else if (recursive)
                results.AddRange(await GetFiles(container, ((CloudBlobDirectory)item).Prefix, recursive));
        }
    }
    while (continuationToken != null);

    return results;
}

我不喜欢上面的代码,因为我遍历了所有文件并添加到结果中,直到取消标记为null。所以基本上,去拿所有的东西,然后停下来再回来。

我不太熟悉使用yield,并且已经提出了这个方法,但是我认为它可能不会推迟对ListBlobSegment的调用。这是我的密码:

internal IEnumerable<BlobItem> GetFiles(CloudBlobContainer container, string directoryName, bool recursive)
{
    var results = new List<BlobItem>();
    BlobContinuationToken continuationToken = null;

    do
    {
        var response = container.GetDirectoryReference(directoryName).ListBlobsSegmentedAsync(false, BlobListingDetails.None, 100, continuationToken, null, null).GetAwaiter().GetResult();

        continuationToken = response.ContinuationToken;
        foreach (var item in response.Results)
        {


            if (item.GetType() != typeof(CloudBlobDirectory))
                yield return new BlobItem(item);
            else if (recursive)
            {
                var internalResponse =  GetFiles(container, ((CloudBlobDirectory)item).Prefix, recursive));
                foreach (var intItem in internalResponse)
                {
                    yield return intItem;
                }
            }
        }
    }
    while (continuationToken != null);
}

有人能告诉我我用的是什么吗 yield

提前感谢您的指点!

注意:将这些API用于blob存储

using Microsoft.WindowsAzure.Storage;
using Microsoft.WindowsAzure.Storage.Blob;

1 回复 | 直到 7 年前

1

4

Alex AIT 7 年前

编辑2018-11-15 从开始 C#8级 ,您将能够使用 IAsyncEnumerable :

async IAsyncEnumerable<int> GetBigResultsAsync()
{
    await foreach (var result in GetResultsAsync())
    {
        if (result > 20) yield return result; 
    }
}

IAsyncEnumerable<string> GetAsyncAnswers()
{
    return AsyncEnum.Enumerate<string>(async consumer =>
    {
        foreach (var question in GetQuestions())
        {
            string theAnswer = await answeringService.GetAnswer(question);
            await consumer.YieldAsync(theAnswer);
        }
    });
}

https://blogs.msdn.microsoft.com/dotnet/2018/11/12/building-c-8-0/

https://archive.codeplex.com/?p=asyncenum

你需要使用 IObservable<BlobItem> 而不是 IEnumerable<BlobItem> 在这种情况下。至少在内部,这取决于你实际打电话的方式 GetFiles .

How to yield return item when doing Task.WhenAny

或者 corresponding blog post 为了得到公认的答案。

旁注:您可能需要使用参数 useFlatBlobListing=true ListBlobsSegmentedAsync

一些快速代码,描述了这可能看起来如何(未测试或任何东西)

public IEnumerable<BlobItem> GetFilesAsEnumerable(CloudBlobContainer container, string directoryName, bool recursive)
{
    return GetFiles(container, directoryName, recursive).ToEnumerable();
}

public IObservable<BlobItem> GetFiles(CloudBlobContainer container, string directoryName, bool recursive)
{
    return Observable.Create<BlobItem>(async obs =>
        {
            BlobContinuationToken continuationToken = null;

            do
            {
                var response = await container.GetDirectoryReference(directoryName).ListBlobsSegmentedAsync(/*useFlatBlobListing*/ recursive, BlobListingDetails.None, 100, continuationToken, null, null);

                continuationToken = response.ContinuationToken;
                foreach (var item in response.Results)
                {
                    // Only required if recursive == false
                    if (item.GetType() != typeof(CloudBlobDirectory))
                        obs.OnNext(new BlobItem(item));
                }
            }
            while (continuationToken != null);
        });
}