.NET 和 Azure Blob 存储 - 对同名图像强制缓存失效

Question

在我使用 asp.net 核心制作的应用程序中，我有一个页面允许用户为他们的产品添加和删除 3 个图像。 当用户添加图像时，我使用特定名称（来自 3 个变量）将其上传到 Azure Blob 存储。

但是如果用户删除并添加了一张图片，由于缓存和我保持相同的名称，图片仍然相同。我不想更改文件名以避免管理 Azure Blob 存储中的删除。

这里是上传方法的代码：

 public async Task<string> UploadFileToCloudAsync(string containerName, string name, Stream file)
        {
            var cloudBlobContainerClient =
                await StorageHelper.ConnectToBlobStorageAsync(_blobStorageEndPoint, containerName);

            if (cloudBlobContainerClient == null)
            {
                throw new NullReferenceException($"Unable to connect to blob storage {name}");
            }
            
            BlobClient blobClient = cloudBlobContainerClient.GetBlobClient(name);
            await blobClient.UploadAsync(file, true);
            var headers = await CreateHeadersIfNeededAsync(blobClient);

            if (headers != null)
            {
                // Set the blob's properties.
                await blobClient.SetHttpHeadersAsync(headers);
            }
            
            return blobClient.Uri.AbsoluteUri;
        }
```

and here the method to create the headers : 

```` private readonly string _defaultCacheControl = "max-age=3600, must-revalidate";

        private async Task<BlobHttpHeaders> CreateHeadersIfNeededAsync(BlobClient blobClient)
        {
            BlobProperties properties = await blobClient.GetPropertiesAsync();
            BlobHttpHeaders headers = null;
            if (properties.CacheControl != _defaultCacheControl)
            {

                headers = new BlobHttpHeaders
                {
                    // Set the MIME ContentType every time the properties 
                    // are updated or the field will be cleared
                    ContentType = properties.ContentType,
                    ContentLanguage = properties.ContentLanguage,
                    CacheControl = _defaultCacheControl,
                    ContentDisposition = properties.ContentDisposition,
                    ContentEncoding = properties.ContentEncoding,
                    ContentHash = properties.ContentHash
                };
            }

            return headers;
        }
```

I need to know if is possible to force cache to be invalidate ? I think with the cache invalidation, the correct image should be displayed after an add / delete / add for the same image.

Thanks in advance

Answer 1

如果您想为不同的内容重复使用相同的名称，您需要使用Cache-Control: no-cache 来prevent caching。指定must-revalidate 只会在有效期后进行验证。

值得注意的是，这对客户端和服务器不利，因为您会丢失所有缓存。更好地使用独特的名称和设计来实现资产的不变性。