Dependencies of job chains implemented by events

One of the methods to implement dependencies between  job chains is using an event handler. Whenever an event is generated an entry is made into the data base table scheduler_events. In the event handler the conditions are defined to add an order for the job chain to be startet.

Notice that the event service will not work with data base H2.

Event service

Before events can be used the event service has to be installed. It is part of the JobScheduler installation if ordered within the installation procedure.

But it is also possible to install  the event service in an existing JobScheduler instance . For more information  for this purpose have a look at  How to install the Event Service feature in JobScheduler

The job chain scheduler_event_service is running in predetermined intervals or whenever an event is created and checks all .xml data files in folder $SCHEDULER_DATA/config/events for information matching the active events which are stored in the data base table .

Event handler

For each job chain which is started by events we need an action defined in the event handler. An action has the two parts:

• Events ("if-clause")
• Command ("then-clause")

An event is uniquely defined by event class and event ID. Together with and/or/not the events of a group are combined to the condition.

In the command part the order is defined to start the job chain as soon as the condition becomes true. It  is also possible to use the  command add event for creating new events.

Every event which is used in the condition has to be deleted from the database with the command remove event.