Publish Messages to a Topic in a Pub/Sub Model

The ITopic/Topic interface in Pub/Sub model facilitates the publishing of messages against the Topic. This also provides event registrations for message delivery failure, receiving messages, and deleting topics.

Note

This feature is also available in NCache Professional.

It provides the Publish method, which publishes the message to a specific Topic in the cache. While publishing messages to a Topic, the publisher can set the delivery option for messages, message expiration, message delivery failure notification, and Topic deletion notification.

Here, we describe how to publish messages, publish messages asynchronously, publish bulk messages, and publish ordered messages.

Prerequisites

To learn about the standard prerequisites required to work with all NCache client-side features including Pub/Sub model, please refer to the given page on Client-Side API Prerequisites.
For API details, refer to: ICache, CacheItem, ITopic, Publish, GetTopic, PublishAsync, ExpirationTime, MessageDeliveryFailure, OnTopicDeleted, DeliveryOption, Message, PublishBulk, MessageFailedEventArgs, TopicDeleteEventArgs.

Publish Messages

The following code sample does the following:

Create dedicated topics for Order related messages.
Register the MessageDeliveryFailure event for the Topic.
Register the OnTopicDeleted event for the Topic.
Create messages for each Topic, enabling expiration and delivery options.
Publish the messages.

// Precondition: Cache is already connected

// Topic "orderTopic" exists in cache
string topicName = "orderTopic";

// Get the topic
ITopic orderTopic = cache.MessagingService.GetTopic(topicName);

if (orderTopic != null)
{
    // Create the object to be sent in message
    Order order = FetchOrderFromDB(10248);

    // Create the new message with the object order
    var orderMessage = new Message(order);

    // Set the expiration time of the message
    orderMessage.ExpirationTime = TimeSpan.FromSeconds(5000);

    // Register message delivery failure
    orderTopic.MessageDeliveryFailure += OnFailureMessageReceived;

    //Register topic deletion notification
    orderTopic.OnTopicDeleted = TopicDeleted;

    // Publish the order with delivery option set as all
    // and register message delivery failure
    orderTopic.Publish(orderMessage, DeliveryOption.All, true);
}
else
{
    // No topic exists
}

// Precondition: Cache is already connected

// Already existing topic
String topicName = "orderTopic";

// Get topic
Topic orderTopic = cache.getMessagingService().getTopic(topicName);

if (topicName != null) {
    // Create object to be sent in the message
    Order order = fetchOrdersFromDB(1100);

    // Create new message
    Message orderMessage = new Message(order);

    TimeSpan expiryTime = new TimeSpan(12, 12, 12);
    // Set expiration time of the message
    orderMessage.setExpirationTime(expiryTime);

    // Register message delivery failure
    MyTopicListener topicListener = new MyTopicListener();
    orderTopic.addMessageDeliveryFailureListener(topicListener);
    orderTopic.addTopicDeletedListener(topicListener);

    // Publish the order with delivery option set as All
    // and register message delivery failure
    orderTopic.publish(orderMessage, DeliveryOption.All, true);
} else {
    // No topic exists
}

# Precondition: Cache is already connected

# Topic "orderTopic" exists in the cache
topic_name = "orderTopic"

# Get the topic
order_topic = cache.get_messaging_service().get_topic(topic_name)

if order_topic is not None:
    # Create object to be sent in message
    order = fetch_order_from_db("1001")

    # Create a new message with the object order
    order_message = ncache.Message(order)

    # Set the expiration time of the message
    expiry_time = ncache.TimeSpan(12, 12, 12)
    order_message.set_expiration_time(expiry_time)

    # Register message delivery failure
    order_topic.add_message_delivery_failure_listener(topic_listener)

    # Register topic deletion notification
    order_topic.add_topic_deleted_listener(topic_listener)

    # Publish the order with delivery option set as All
    # and register message delivery failure
    order_topic.publish(order_message, ncache.DeliveryOption.ALL, True)
else:
    # No topic exists
    print("Topic not found")

// This is an async method
// Precondition: Cache is already connected

// Topic "orderTopic" exists in the cache
let topicName = "orderTopic";

// Get the topic
let orderTopic = await ncache.getMessagingService().getTopic(topicName);

if (!(orderTopic == null)) {
// Create object to be sent in message
let order = await this.fetchOrdersFromDb(this.orderId);

// Create a new message with the object order
let orderMessage = new ncache.Message(order);

// Set the expiration time of the message
let expiryTime = new ncache.TimeSpan(12, 12, 12);
orderMessage.setExpirationTime(expiryTime);

let topicListener = new ncache.MyTopicListener();

// Register message delivery failure
orderTopic.addMessageDeliveryFailureListener(topicListener);

// Register topic deletion notification
orderTopic.addTopicDeletedListener(topicListener);

// Publish the order with delivery option set as All
// and register message delivery failure
orderTopic.publish(orderMessage, ncache.DeliveryOption.All, true);
} else {
// No topic exists
}

Note

To ensure the operation is fail-safe, it is recommended to handle any potential exceptions within your application, as explained in Handling Failures.

Publish Asynchronously

Messages can be published on the Topic asynchronously using PublishAsync so that the application does not wait for the operation completion to perform the next operation. The user has the control returned to them immediately for further processing. The following example lets you publish a message asynchronously.

// Topic "orderTopic" exists in cache
string topicName = "orderTopic";

// Get the topic
ITopic orderTopic = cache.MessagingService.GetTopic(topicName);

if (orderTopic != null)
{
    // Create the object to be sent in message
    Order order = FetchOrderFromDB(10248);

    // Create the new message with the object order
    var orderMessage = new Message(order);

    // Set the expiration time of the message
    orderMessage.ExpirationTime = TimeSpan.FromSeconds(5000);

    // Register message delivery failure
    orderTopic.MessageDeliveryFailure += OnFailureMessageRecieved;

    //Register topic deletion notification
    orderTopic.OnTopicDeleted = TopicDeleted;

    // Publish the order with delivery option set as all
    // and register message delivery failure
    Task task = orderTopic.PublishAsync(orderMessage, DeliveryOption.All, true);

    if(task.IsFaulted)
    {
        // Task Failed
    }
}
else
{
    // No topic exists
}

// Topic orderTopic already exists in the cache
String topicName = "orderTopic";

// Get the topic
Topic orderTopic = cache.getMessagingService().getTopic(topicName);

if (orderTopic != null) {
    // Create object to be sent in the message
    Order order = fetchOrdersFromDB(1100);

    // Create new message
    Message orderMessage = new Message(order);

    TimeSpan expiryTime = new TimeSpan(12, 12, 12);
    // Set expiration time of the message
    orderMessage.setExpirationTime(expiryTime);

    // Register message delivery failure
    MyTopicListener topicListener = new MyTopicListener();
    orderTopic.addMessageDeliveryFailureListener(topicListener);
    orderTopic.addTopicDeletedListener(topicListener);

    // Publish the order with delivery option set as All
    // and register message delivery failure
    TimeScheduler.Task task = (TimeScheduler.Task) orderTopic.publishAsync(orderMessage, DeliveryOption.All, true);

    if (task.IsCancelled()) {
        // task cancelled
    }
} else {
    // No topic exists
}

# Topic "orderTopic" exists in the cache
topic_name = "orderTopic"

# Get the topic
order_topic = cache.get_messaging_service().get_topic(topic_name)

if order_topic is not None:
    # Create object to be sent in message
    order = fetch_order_from_db("1001")

    # Create a new message with the object order
    order_message = ncache.Message(order)

    # Set the expiration time of the message
    expiry_time = ncache.TimeSpan(12, 12, 12)
    order_message.set_expiration_time(expiry_time)

    # Register message delivery failure
    order_topic.add_message_delivery_failure_listener(topic_listener)

    # Register topic deletion notification
    order_topic.add_topic_deleted_listener(topic_listener)

    # Publish the order with delivery option set as All
    # and register message delivery failure
    task = order_topic.publish_async(order_message, ncache.DeliveryOption.ALL, True)

    # Use this task object as per your business logic
else:
    # No topic exists
    print("Topic not found")

Publish Bulk Messages

Multiple messages can be published in a single call using the PublishBulk method. This improves the performance and memory usage as a bulk of messages will be combined and published in a single call. The code below takes an instance of an already created Topic orderTopic, and shows the bulk publishing of messages to the Topic.

// Topic "orderTopic" exists in cache
ITopic topic = cache.MessagingService.GetTopic("orderTopic");

if (topic != null)
{
    // create dictionary for storing bulk
    List<Tuple<Message, DeliveryOption>> messageList = new List<Tuple<Message, DeliveryOption>>();
    Order[] orders = FetchOrdersFromDB();
        for (int i = 0; i < 100; i++)
    {
        Message message = new Message(orders[i]);
        message.ExpirationTime = TimeSpan.FromSeconds(10000);
        messageList.Add(new Tuple<Message, DeliveryOption>(message, DeliveryOption.All));
    }
    // Register message delivery failure
    topic.MessageDeliveryFailure += OnFailureMessageRecieved;

    //Register topic deletion notification
    topic.OnTopicDeleted = TopicDeleted;

    // Publish the order with delivery option set as all
    // and register message delivery failure
    // In case of failed publishing of messages, exceptions
    // will be returned
    IDictionary<Message, Exception> keys = topic.PublishBulk(messageList, true);
}

// topic already exists
String topicName = "orderTopic";
String customerID = "DUMON";
Topic topic = cache.getMessagingService().getTopic(topicName);

if (topic != null) {
    // create dictionary for storing bulk
    Map messageMap = new HashMap();

    Order[] orders = fetchOrdersFromDb(customerID);

    for (int i = 0; i < 100; i++) {
        Message message = new Message(orders[i]);
        message.setExpirationTime(TimeSpan.FromSeconds(10000));
        messageMap.put(message, DeliveryOption.All);
    }
    MyTopicListener topicListener = new MyTopicListener();

    // Register message delivery failure
    topic.addMessageDeliveryFailureListener(topicListener);

    // Register topic deletion notification
    topic.addTopicDeletedListener(topicListener);

    Map<Message, Exception> keys = topic.publishBulk(messageMap, true);
} else {
    // topic is null
}

# Topic "orderTopic" exists in the cache
topic_name = "orderTopic"

# Get the topic
topic = cache.get_messaging_service().get_topic(topic_name)

if topic is not None:
    # Create Dict for storing messages in bulk
    messages_map = {}

    orders = fetch_orders_by_customer_id("ALFKI")
    for i in range(0, 100):
        message = ncache.Message(orders[++i])
        message.set_expiration_time(ncache.TimeSpan.from_seconds(10000))
        messages_map[message] = ncache.DeliveryOption.ALL

    # Register message delivery failure
    topic.add_message_delivery_failure_listener(topic_listener)

    # Register topic deletion notification
    topic.add_topic_deleted_listener(topic_listener)

    # Publish the order with delivery option set as All
    # and register message delivery failure
    # In case of failed publishing of messages, exception will be returned
    keys = topic.publish_bulk(messages_map, True)
else:
    # No topic exists
    print("Topic not found")

// This is an async method
// Topic "orderTopic" exists in the cache
let topicName = "orderTopic";

// Get the topic
let topic = ncache.getMessagingService().getTopic(topicName);

if (topic != null) {
// Create Map for storing messages in bulk
let messageMap = new Map();

let orders = this.fetchOrdersByCustomerId(this.customerId);
var i;
for (i = 0; i < 100; i++) {
    let message = new ncache.Message(orders[i]);
    message.setExpirationTime(ncache.TimeSpan.FromSeconds(10000));
    messageMap.set(message, ncache.DeliveryOption.All);
}
let topicListener = new ncache.TopicListener();

// Register message delivery failure
topic.addMessageDeliveryFailureListener(topicListener);

// Register topic deletion notification
topic.addTopicDeletedListener(topicListener);

// Publish the order with delivery option set as All
// and register message delivery failure
// In case of failed publishing of messages, exception will be returned
let keys = topic.publishBulk(messageMap, true);
} else {
// No topic exists
}

Publish Ordered Messages

Note

This feature is only available in NCache 5.2 and onwards.

Messages can be published by mentioning a sequence name resulting in the messages being published in a specific order. To specify ordered messages, a string sequence name is added to the chain of the messages that makes sure to publish all the messages belonging to a specific sequence name on the same server node. In the example given below, a sequence name is added with the messages, and the messages are then published using the Publish method.

// Specify the topic name that already exists
string topicName = "orderTopic";
// Get the topic with the specified name
ITopic orderTopic = cache.MessagingService.GetTopic(topicName);
if (topicName != null)
{
    for (int i = 0; i < 30; i++)
    {
        // Create the object to be sent in message
        Order order = FetchOrderFromDB(10248);

        // Create the new message with the object order
        var orderMessage = new Message(order);

        // Specify a unique sequence name for the messages
        string sequenceName = "OrderMessages";

        // Set the expiration time of the message
        orderMessage.ExpirationTime = TimeSpan.FromSeconds(5000);

        // Publish message with the sequence name
        orderTopic.Publish(orderMessage, DeliveryOption.All, sequenceName, true);
    }
}
else
{
    // No topic found
}

// Specify the topic name that already exists
String topicName = "orderTopic";

// Get the topic with the specified name
Topic orderTopic = cache.getMessagingService().getTopic(topicName);

if (topicName != null) {
    for (int i = 0; i < 30; i++) {
        // Create the object to be sent in the message
        Order order = fetchOrdersFromDB(10248);

        // Create the new message with the object order
        var orderMessage = new Message(order);

        // Specify a unique sequence name for the message
        String sequenceName = "OrderMessage";

        // Set the expiration time of the message
        orderMessage.setExpirationTime(TimeSpan.FromSeconds(5000));

        // Publish message with the sequence name
        orderTopic.publish(orderMessage, DeliveryOption.All, sequenceName, true);
    }
} else {
    // No topic found
}

# Specify the topic name that already exists
topic_name = "orderTopic"

# Get the topic with the specified name
order_topic = cache.get_messaging_service().get_topic(topic_name)

if topic_name is not None:
    for i in range(0, 30):
        # Create the object to be sent in the message
        order = fetch_order_from_db(10248)

        # Create the new message with the object order
        order_message = ncache.Message(order)

        # Specify a unique sequence name for the message
        sequence_name = "OrderMessage"

        # Set the expiration time of the message
        order_message.set_expiration_time(ncache.TimeSpan.from_seconds(5000))

        # Publish message with the sequence name
        order_topic.publish(order_message, ncache.DeliveryOption.ALL, True, sequence_name)
else:
    # No topic found
    print("Topic not found")

// This is an async method

// Specify the topic name that already exists
let topicName = "orderTopic";

// Get the topic with the specified name
let orderTopic = await this.cache.getMessagingService().getTopic(topicName);

if (topicName != null) {
var i;
for (i = 0; i < 30; i++) {
    // Create the object to be sent in the message
    let order = await this.fetchOrderFromDB(10248);

    // Create the new message with the object order
    var orderMessage = new ncache.Message(order);

    // Specify a unique sequence name for the message
    let sequenceName = "OrderMessage";

    // Set the expiration time of the message
    orderMessage.setExpirationTime(ncache.TimeSpan.FromSeconds(5000));

    // Publish message with the sequence name
    orderTopic.publish(
    orderMessage,
    ncache.DeliveryOption.All,
    sequenceName,
    true
    );
}
} else {
// No topic found
}

Register Callbacks

private void OnFailureMessageReceived(object sender, MessageFailedEventArgs args)
{
    // Failure reason can be get from args.MessageFailureReason
}

private void TopicDeleted(object sender, TopicDeleteEventArgs args)
{
    // Deleted topic is args.TopicName
}

@Override
public void onTopicDeleted(Object sender, TopicDeleteEventArgs args) {
    // Deleted topic is args.getTopicName();
}

@Override
public void onMessageDeliveryFailure(Object sender, MessageFailedEventArgs args) {
    // Failure reason is args.getMessageFailureReason();
}

@Override
public void onMessageReceived(Object sender, MessageEventArgs args) {
    // Perform operations
}

def on_topic_deleted(sender: object, args: ncache.TopicDeleteEventArgs):
    # Perform operations
    print("Deleted topic is " + args.get_topic_name())

def on_message_delivery_failure(sender: object, args: ncache.MessageFailedEventArgs):
    # Perform operations
    print("Failure reason is " + str(args.get_message_failure_reason()))

def on_message_received(sender: object, args: ncache.MessageEventArgs):
    # Perform operations
    print("Message received from topic " + args.get_topic_name())

onTopicDeleted(sender, args) {
    // Deleted topic is args.getTopicName()
}

onMessageDeliveryFailure(sender, args) {
    // Failure reason is args.getMessageFailureReason()
}

onMessageReceived(sender, args) {
    // Perform operations
}

Additional Resources

NCache provides sample application for Pub/Sub on GitHub.

Publish Messages to a Topic in a Pub/Sub Model

Note

Prerequisites

Publish Messages

Note

Publish Asynchronously

Publish Bulk Messages

Publish Ordered Messages

Note

Register Callbacks

Additional Resources

See Also

Contact Us