Subscriptions based in alteration type

By default, a subscription is triggered (i.e. the notification associated to it is sent) when the triggered condition (expressed in the subject and conditions fields of the subscription, e.g. covered entities, list of attributes to check, filter expression, etc.) during a create or actual update entity operation.

However, this default behaviour can be changed so a notification can be sent, for instance, only when an entity is created or only when an entity is deleted, but not when the entity is updated.

In particular, the alterationTypes field is used, as sub-field of conditions. The value of this field is an array which elements specify a list of alteration types upon which the subscription is triggered. At the present moment, the following alteration types are supported:

• entityUpdate: notification is sent whenever a entity covered by the subscription is updated (no matter if the entity actually changed or not)
• entityChange: notification is sent whenever a entity covered by the subscription is updated and it actually changes (or if it is not an actual update, but forcedUpdate option is used in the update request)
• entityCreate: notification is sent whenever a entity covered by the subscription is created
• entityDelete: notification is sent whenever a entity covered by the subscription is deleted

For instance:

  "conditions": {
    "alterationTypes": [ "entityCreate", "entityDelete" ],
    ...
  }

will trigger subscription when an entity creation or deletion takes place, but not when an update takes place. The elements in the alterationTypes array are interpreted in OR sense.

Default alterationTypes (i.e. the one for subscription not explicitly specifying it) is ["entityCreate", "entityChange"].

The particular alteration type can be got in notifications using the alterationType builtin attribute.