Manage container properties and metadata by using .NET

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Blob containers support system properties and user-defined metadata, in addition to the data they contain.

• System properties: System properties exist on each Blob storage resource. Some of them can be read or set, while others are read-only. Under the covers, some system properties correspond to certain standard HTTP headers. The Azure Storage client library for .NET maintains these properties for you.

• User-defined metadata: User-defined metadata consists of one or more name-value pairs that you specify for a Blob storage resource. You can use metadata to store other values with the resource. Metadata values are for your own purposes only, and don't affect how the resource behaves.

Metadata name/value pairs are valid HTTP headers, and so should adhere to all restrictions governing HTTP headers. Metadata names must be valid HTTP header names and valid C# identifiers, can contain only ASCII characters, and should be treated as case-insensitive. Metadata values containing non-ASCII characters should be Base64-encoded or URL-encoded.

Retrieve container properties

To retrieve container properties, call one of the following methods of the BlobContainerClient class:

• GetProperties
• GetPropertiesAsync

The following code example fetches a container's system properties and writes some property values to a console window:

private static async Task ReadContainerPropertiesAsync(BlobContainerClient container)
{
    try
    {
        // Fetch some container properties and write out their values.
        var properties = await container.GetPropertiesAsync();
        Console.WriteLine($"Properties for container {container.Uri}");
        Console.WriteLine($"Public access level: {properties.Value.PublicAccess}");
        Console.WriteLine($"Last modified time in UTC: {properties.Value.LastModified}");
    }
    catch (RequestFailedException e)
    {
        Console.WriteLine($"HTTP error code {e.Status}: {e.ErrorCode}");
        Console.WriteLine(e.Message);
        Console.ReadLine();
    }
}

Set and retrieve metadata

You can specify metadata as one or more name-value pairs on a blob or container resource. To set metadata, add name-value pairs to an IDictionary object, and then call one of the following methods of the BlobContainerClient class to write the values:

• SetMetadata
• SetMetadataAsync

The name of your metadata must conform to the naming conventions for C# identifiers. Metadata names preserve the case with which they were created, but are case-insensitive when set or read. If two or more metadata headers with the same name are submitted for a resource, the Blob service returns status code 400 (Bad Request).

The following code example sets metadata on a container.

public static async Task AddContainerMetadataAsync(BlobContainerClient container)
{
    try
    {
        IDictionary<string, string> metadata =
           new Dictionary<string, string>();

        // Add some metadata to the container.
        metadata.Add("docType", "textDocuments");
        metadata.Add("category", "guidance");

        // Set the container's metadata.
        await container.SetMetadataAsync(metadata);
    }
    catch (RequestFailedException e)
    {
        Console.WriteLine($"HTTP error code {e.Status}: {e.ErrorCode}");
        Console.WriteLine(e.Message);
        Console.ReadLine();
    }
}

The GetProperties and GetPropertiesAsync methods are used to retrieve metadata in addition to properties as shown earlier.

The following code example retrieves metadata from a container.

public static async Task ReadContainerMetadataAsync(BlobContainerClient container)
{
    try
    {
        var properties = await container.GetPropertiesAsync();

        // Enumerate the container's metadata.
        Console.WriteLine("Container metadata:");
        foreach (var metadataItem in properties.Value.Metadata)
        {
            Console.WriteLine($"\tKey: {metadataItem.Key}");
            Console.WriteLine($"\tValue: {metadataItem.Value}");
        }
    }
    catch (RequestFailedException e)
    {
        Console.WriteLine($"HTTP error code {e.Status}: {e.ErrorCode}");
        Console.WriteLine(e.Message);
        Console.ReadLine();
    }
}