Does deferred save in Objectify apply per Java entity or per Google Cloud Datastore entity?

Question

Our app logic has multiple layers. Each time a save is invoked, the entity on the domain layer is mapped to a database entity.

For example:

class Sample(); // the domain entity

@Entity("Sample")
@Cache
class DatabaseSample; // the database entity

Let's assume the domain entity is modified and save is invoked, which will map all properties to a new database entity, which is then saved deferred.

Let's assume the same domain entity is modified again and saved again, which will again map all properties to a new database entity and invoke deferred save.

Will the two separate Google Cloud Datastore entities compete with each other, e.g. the newer save overwrite the older save completely, or will objectify collect modified Key-Value pairs during the request and save a consolidated entity at the end of the request?

According to the documentation, in the case of both save() and delete() operations deferred for the same entity, the last operation wins. But, if you are mapping the two domain entities to different database entities then there won't be any overwrite. Am I understanding your app logic right? — llompalles

stickfigure stickfigure · Accepted Answer · 2018-12-23T01:11:36

I don't quite understand the question, but I'll try to give you some context that might help.

If you defer save of an entity POJO, it just marks it as "save this thing" in the session. When the session closes (end of transaction) anything marked for deferred save (or delete) gets saved.

Only at the very moment of saving to the datastore does the POJO get mapped to a low-level Entity. You can defer save the same object a zillion times with no practical effect. In fact, this is the core use case - you might have a method that sets changes some data and wants a save, and some other method that changes some data and wants a save... by using deferred saves, you avoid making separate real saves to the datastore.

If you're asking about doing something really crazy like changing the @Id after deferring a save... don't. I really have no idea what that will do, but you probably won't like it :-)

Does deferred save in Objectify apply per Java entity or per Google Cloud Datastore entity?

1 Answers