Correlation and Exact Match

You can use one or more exact matches in your pattern. To use an exact match, specify a property and an exact value for that property.

In the following example, only the order event with the specified customerId property value will be processed. 

order.customerId = "123-ABC-456"

A pattern cannot begin with an exact match; a correlation is required as the first element in the clause.

Note: If the first item in the then subclause of the starts with clause is one of the following: 
then any one
then all

Then all events in that sequence must use correlation.

Example

To illustrate how exact matches are used, consider the following simple example. Orders are placed and processed for shipment, then they sit on the loading bay, waiting for the next delivery truck. If the truck does not pick up the orders within two hours, customer service is alerted. 

define pattern /OrderShipper
using /Order as order and /orderProcessed as processed and /deliveryvan as van
with
    order.customerId
    and processed.customerId
    and van.pickupStatus=Ready
starts with order
then processed
then within 2 hours van

The pattern is deployed and the Pattern Matcher service starts listening to the events that are sent to it. It puts sets of events that satisfy all the aspects of the pattern into "buckets." At a certain point in time, it has the following "buckets":

  • order.customerId=123, processed.customerId=123
  • order.customerId=456, processed.customerId=456
  • order.customerId=789

Then a truck arrives and the loading bay staff enters its status. A deliveryvan event is sent with status=ready.

The Pattern Matcher updates all of its "buckets" for this pattern accordingly:

  • order.customerId=123, processed.customerId=123, van.pickupStatus=ready
  • order.customerId=456, processed.customerId=456, van.pickupStatus=ready

The above pattern instances succeed and the success rule function executes for each of the instances.

The bucket that contained only order.customerId=789 fails, and the failure rule function pattern executes.

You might feel that the incomplete "bucket" with order.customerId=789 should just wait for its corresponding event, processed.customerId=789 and be delivered on a later truck. If that is the case you must write a different pattern. This simple example only illustrates how the Pattern Matcher service processes a pattern that contains a correlation and an exact match.

You can specify an exact match in many ways, such as the following: 

a.id = "some string"
a.id = 10
a.id = 10.0
a.id = 0.1d
a.id = 333333L
a.id = 333333l
a.id = false
a.id = False
a.id = $param1
a.id = $date(2009, 12, 25)
a.id = $dateTime(2009, 12, 25, 9, 48, 37, 0)
a.id = $javaUtilDate

Parameter values are provided at deploy-time.

Related concepts