Dependencies

Establishing a Dependency Relationship

This example illustrates how to establish a dependency relationship between a parent object and two child objects using a CreatePolicy that contains a list of DependencySpec entries. Removing the parent object causes all of its children (and their children, if any) to be removed.

async Task AddWithDependency(Cache<string, string> cache)
{
    // Add parent object:
    await cache.AddAsync("Primates", "large brains, stereoscopic vision");

    // Create dependency specification for use with child objects:
    var policyBuilder = cache.GetPolicyBuilder();
    policyBuilder.AddDependency(cache, "Primates");

    // Add dependent child objects:
    var policy = policyBuilder.Build();
    await cache.AddAsync("Strepsirrhini", "wet-nosed primates", policy);
    await cache.AddAsync("Haplorhini", "dry-nosed primates", policy);

    // Removing/updating a parent causes children to expire:
    await cache.RemoveAsync("Primates");

    var response = await cache.ReadAsync("Strepsirrhini");
    Console.WriteLine(response.Result);
    // output: NotFound
}

Retrieving Dependency Information

This example illustrates how to use the GetMetadataAsync(TKey, CancellationToken) method to retrieve dependency information about an existing object that resides in the ScaleOut service.

async Task GetDependencyMetadata(Cache<string, string> cache)
{
    // Add 2 parent objects to be associated with a child:
    await cache.AddAsync("Parent1 key", "Parent1 payload");
    await cache.AddAsync("Parent2 key", "Parent2 payload");

    // Create dependency specification for use with child object:
    var policyBuilder = cache.GetPolicyBuilder();
    policyBuilder.AddDependency(cache, "Parent1 key");
    policyBuilder.AddDependency(cache, "Parent2 key");

    // Add dependent child object to cache:
    var policy = policyBuilder.Build();
    await cache.AddAsync("Child key", "Child payload", policy);

    // Retrieve metadata from the server to get dependency information
    // about an existing child object:
    var metadataResponse = await cache.GetMetadataAsync("Child key");
    var metadata = metadataResponse.Value;

    // Use DependencySpec.ToKey() to decode parent specs back to their original string type:
    var decodedParentKeys = metadata.Parents.Select(depSpec => depSpec.ToKey(cache));

    foreach (var dpk in decodedParentKeys)
        Console.WriteLine(dpk);

    // output: 
    //    Parent1 key
    //    Parent2 key
}

Dependency Notifications

An application can be notified of the removal of an object due to a dependency relationship by supplying a callback to the ServiceEvents.SetExpirationHandlerAsync method See Expiration Events for details.