Service Bus Topics - Define custom rules for messages that don’t respect any rule defined in a topic

In one of my older post I tacked about how we can define filters for each subscriber of a Service Bus Topics. We saw how we can filter messages for a subscriber based on some rules that are defined using FilterExpression:

RuleDescription ruleDescription = new RuleDescription()

{

    Action = new SqlRuleAction("set isValid= false"),

    Filter = new SqlFilter("value = 10");

}

namespaceManager.CreateSubscription(

    "myFooTopic",

    "seccondSubscription",

    ruleDescription);

var subscription = namespaceManager.CreateSubscription(

    "myFooTopic",

    " thirdSubscription");

subscription.Add(ruleDescription);

Using these rules is quite simple to define custom rules for the messages from a topic. But what about messages that don’t respect any rules defined in our topic? How we can detect these messages and define a custom rule for them. In a perfect word we can control the messages that arrive in our topic, but in a distributed system these thing doesn’t happen all the time.
For this cased we can use “MatchNoneFilterExpression” that will route to our topic all the messages that were not consumed by our subscribers. For example in our example we only consume messages that have the value equal with 10. What about the rest of the messages? Of course we can define a rule for values that are not equal with 10, but if we have more subscribes with different rules it will complicated to define the non-true rules for all the subscribers.

 RuleDescription notConsumedMessagesRule = new RuleDescription()

 {

     FilterAction = new SqlFilterAction(“set isNotConsumed = true;”),

     FilterExpression = new MatchNoneFilterExpression()

 };

 subscription.Add(notConsumedMessagesRule);

In the above example our rule adds a property named “isNotConsumed” and set the value to true. Based on this rule we will able to route this messages to a specific subscriber.
In the same way we have another filter expression that is used when we want to define a rule for the messages that match all the filter expression from all our rules – MatchAllFilterExpression.

RuleDescription matchAllRule = new RuleDescription()
 {
     FilterAction = new SqlFilterAction(“set matchAll = true;”),
     FilterExpression = new MatchAllFilterExpression()
 };
 subscription.Add(matchAllRule);

Using this filter expression we can define custom rules for messages that didn’t respect any defined rule or messages that respect all the rules from our topic. In the end I want to enumerate the filter expression that can be used in this moment:

• CorrelationFilterExpression
• MatchNoneFilterExpression
• MatchAllFilterExpression
• SqlFilterExpression