Qi4j in 2 hours

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This introduction assumes that the "Qi4j in 10 minutes" and "Qi4j in 30 minutes" introductions has been read and understood.

In this introduction we will touch on the core concepts of UnitOfWork, Application structure and Bootstrap API.

Persistence and UnitOfWork -

We have previously seen that it is easy to declare that a Composite should be persisted, but not touched on how to interact with the underlying persistence system. This is done via EntitySessions.

Application Structure -
- There are one Application per Qi4j instance.
- An Application consists of one or more Layers.
- Each Layer consist of one or more Modules.
- Layers are organized in a top-down manner, lower Layers on top of higher Layers.
- One must declare which Composites that each Module is responsible for.
- A Composite can either be private or public in the Module.
- A private Composite can only be reached from within the same Module.
- A public Composite can be reached from other Modules in the same Layer.
- A public Composite can be declared to be public in the Layer.
- A Composite that is declared public in the Layer can be reached from the Layers directly on top (not transitive to Layers higher up).
- The Application can also declare public Composites (later for SCA).

For simpler Applications it is possible (quite easily) to create a single Layer with a single Module, but for more complex Applications we strongly recommend the partitioned approach.

Bootstrap API

— to be continued