DomainEntity-Oriented casting
If some changes are done for the domain-entity, it will cause for a version-update. Even though the version is updated, there is something to be considered carefully. After updating the domain-entity’s version, it is not a problem for that particular version at all. But StackSaga follows the event sourcing architecture and event re-invoking mechanism, in the event-store can have some events from the old version of the domain-entity to be re-invoked. Therefore, the SEC has to cast (map/convert/deserialize) the old domain-entity event to the new version. It is called as DomainEntity-Oriented casting.
| Even thought the term is quite simple at first glance, It can be effected to get crashed all the old events if you are unable to manage the version mapping. The casting process is failed for the old version’s events, there is no chance to be re-invoked that retry process with the old versions. |
| Even though the casting process is done by the SEC, as the developer, you are responsible for managing the casting the new version with the old versions' events. |
Based on the behavior of the domain-entity state-change, the DomainEntity-Oriented version casting can be divided to two.
DomainEntity-Oriented Up-Casting
If the new domain-entity has more new attributes than the old one, that kind of event should be cast with upcasting.
For instance, the old version’s domain-entity has 3 fields, and the new version can have 4 fields or more than that, the old version’s events should be cast to the new domain-entity object, and that term is called as upcasting.
The following image shows how it is done by the SEC.
Explanation: In the event-store can have old remaining events to be re-tried.
But due to the fact that the domain-entity has been updated to a new version with new attributes, The old events also should be converted and should be run through the new domain-entity.
But if it is an upcast mapping, The new version doesn’t bother to the casting process at all due that SEC uses jackson objectmapper to serialization and deserialization both.
The new values will have the default values with help of
jackson objectmapper and you have nothing to worry about upcasting with StackSaga at all. See the <<,technical documentation>>
| All the events that go through the SEO process can be identified easily in the Executor’s methods with the help of event-version data that provides with the domain-entity object. See the [technical documentation] |
DomainEntity-Oriented Down-Casting
According to the example, the event-store might have the old events consisting of 2 fields. And if the new version has a less number of fields than the old one, it is called as down-casting. Now those remaining events are going to be executed through the new version. And the framework tries to build the new domain-entity object by using the old event’s binaries. This is the time the casting is been worked on. You have to modify and annotate the domain-entity so as not to conflict while building the object by the framework. Here you can see the best practices related to the casting of domain-entities.