Add open initializer function to Entity

[lehmanju]

This would allow any subclass of Entity to detect whether it is being initialized (by new{}) or just created from previously existing database values. Custom entities could overwrite this method to do certain initializing stuff because the default init block is called every time (also on loading from the database).

[lehmanju]

Added more flexibility, it is now possible to have separate functions to be called on initialization, one before the user provided init block in new is executed and one after that.

[Tapac]

@lehmanju , could you provided a real world use-cases when this might be useful?
From my point of view it's not very handy to move this to Entity class, beside you it's always possible to create custom EntityClass.new(before, after, init){} function with same behavior.
Maybe it's just enough to make new open?

[lehmanju]

I have added extra functionality to my Entity. On creation some actions should be performed via a REST Api but only once, of course. The point of having an initializer inside the Entity is that I don't want to write common code in every invocation of new(). So I need a way to detect whether this Entity is created from scratch or just loaded from the database. Maybe there are better ways to do this ...

[Tapac]

With opening fun new(id: ID?, init: T.() -> Unit): T it will be possible to write something like (see below) to receive same behavior:

class TestEntity(id: EntityID<Int>) : Entity<Int>(id) {
        companion object : IntEntityClass<TestEntity>(IntIdTable) {
            override fun new(init: TestEntity.() -> Unit)  =
                super.new{ before(); init() }.apply {
                    after()
                }
        }
    }

I just think that having before and after functions at Entity level is bad approach, because it create feeling that I have to invoke it somehow manually, IMO. Also we want to keep Entity as clean as possible while thinking about data class support (#24)

[lehmanju]

@Tapac I'd be happy to have new as an open function, your proposal is actually better ;) Thank you very much, in the future I would probably use data classes as well.

[Tapac]

@lehmanju , I've pushed changes with open new on EntityClass, so now I will close this PR.