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Design a state machine mechanism using Windows Azure Service Bus (part 2)

In my last post I presented how we can implement a state machine using Windows Azure Service Bus Topics. In this post we will see the real code that we need to write to make this possible.
We will start from a simple example. Let’s imagine that we have 3 states machines:
  1. Added
  2. Initialized
  3. Processed
Each state change will required a custom action to be executed. When changing the state from Added to Initialized we will need to calculate some values. Changing the state from Initialized to Processed will required to store the sum value in a repository. Messages in state Processed will be logged.
We will implement this using Windows Azure Service Bus Topics. For each state we will have a different subscription that will process messages with the given state. Each action that needs to be done at each step will be made by the process (machine) that receives the given message from subscription.
In the next part of the post we will cover all the steps that need to be done to be able to implement this.
First of all we need to create a new Service Bus Topic. Before creating a Service Bus Topic you should always check if a topic with the specific name was already created.
var namespaceManager =
    NamespaceManager
        .CreateFromConnectionString(CloudConfigurationManager.GetSetting("ServiceBusConnectionString"));

if (!namespaceManager.TopicExists("myFooTopic"))
{
    namespaceManager.CreateTopic("myFooTopic");
}
After this step, we will need to create a subscription for each state. For the first step, the sum that needs to be computed can be done directly from subscription. We can specify in the action of the subscription the sum calculation.
RuleDescription ruleDescription = new RuleDescription()
{
    Action = new SqlRuleAction("set sum = value1 + value2"),   
    Filter = new SqlFilter("state = added");
}

namespaceManager.CreateSubscription(
    "myFooTopic",
    "addedSubscription ",
    ruleDescription);
Even if the calculation is made automatically, by Service Bus Topic, we will need to take the message from the current subscription, change the state and add it back to the topic:
TopicClient topicClient = TopicClient.CreateFromConnectionString(
    CloudConfigurationManager.GetSetting("ServiceBusConnectionString"),
    "myFooTopic");

SubscriptionClient subscriptionClient = SubscriptionClient.CreateFromConnectionString(
    CloudConfigurationManager.GetSetting("ServiceBusConnectionString"),
    "myFooTopic",
    "addedSubscription");

BrokeredMessage brokeredMessage = subscriptionClient.Receive();
if(message != null)
{
  try
    {
    BrokeredMessage newMessage = new BrokeredMessage();
    newMessage.Properties["sum"] = message.Properties["sum"];
    newMessage.Properties["state"] = "initialized";
    topicClient.Send(newMessage);   
        message.Complete();
    }
    catch (Exception)
    {
        message.Abandon();
    }   
}
In this moment we have a mechanism that process messages that are in the first state. A similar code need to be implemented for the next 2 states. For the next state we will need to create the subscription:
RuleDescription ruleDescription = new RuleDescription()
{
    Filter = new SqlFilter("state = processed");
}

namespaceManager.CreateSubscription(
    "myFooTopic",
    " processedSubscription ",
    ruleDescription);
After this we will need to implement the action that need to be done for messages with the given state:
TopicClient topicClient = TopicClient.CreateFromConnectionString(
    CloudConfigurationManager.GetSetting("ServiceBusConnectionString"),
    "myFooTopic");

SubscriptionClient subscriptionClient = SubscriptionClient.CreateFromConnectionString(
    CloudConfigurationManager.GetSetting("ServiceBusConnectionString"),
    "myFooTopic ",
    "processedSubscription");

BrokeredMessage brokeredMessage = subscriptionClient.Receive();
if(message != null)
{
  try
    {
    var sum = message.Properties["sum"];
    // Save the sum in the repository.
    BrokeredMessage newMessage = new BrokeredMessage();
    newMessage.Properties["sum"] = sum;
    newMessage.Properties["state"] = "processed";
    topicClient.Send(newMessage);
        message.Complete();
    }
    catch (Exception)
    {
        message.Abandon();
    }   
}
For the next step, the code is very similar; I will not describe the code again. For the last state action we don’t need to add the message again to the topic, because the message is in the last state. We need only to write the data to the log.
TopicClient topicClient = TopicClient.CreateFromConnectionString(
    CloudConfigurationManager.GetSetting("ServiceBusConnectionString"),
    "myFooTopic");

SubscriptionClient subscriptionClient = SubscriptionClient.CreateFromConnectionString(
    CloudConfigurationManager.GetSetting("ServiceBusConnectionString"),
    "initialized",
    "processedSubscription");

BrokeredMessage brokeredMessage = subscriptionClient.Receive();
if(message != null)
{
  try
    {
    Trace.Write(message.Properties["[PropertyName]"]);
    Trace.Write("The ABC was processed");
        message.Complete();
    }
    catch (Exception)
    {
        message.Abandon();
    }   
}
The last step is to write a message on the Service Bus Topic that has the first state.
TopicClient topicClient = TopicClient.CreateFromConnectionString(
    CloudConfigurationManager.GetSetting("ServiceBusConnectionString"),
    "myFooTopic");

BrokeredMessage message = new BrokeredMessage();
message.Properties["value1"] = 10;
message.Properties["value2"] = 40;
topicClient.Send(message);


After the message will be added to the topic, based on the status property, each subscription will process it. Each subscription will process only messages that have their specific status.
 In this post we saw how we can implement in Windows Azure Service Bus Topics a simple workflow that is based on the states.

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