Sometimes, in own orchestrations we need to know if a message context property exists inside one message in particular. Well, the exists operator is useful in this situation.
The exists operator can be use in Filter expressions or Decide shapes. The filter expression can determine if a message is welcome in the orchestration or not, and you can use the exists operator to allow messages that contain one or various message context property incoming to process.
But, if you need to take a decision about what way to follow when a message context property exists or not in the message you can use a Decide shape and the exists operator. The syntax to exists operator is: PropertyName exists MessageName.
For example, if you need to know if the BTS.AckFailurecategory property is inside the message, you must use this expression: BTS.AckFailureCategory exists MessageIn