10 Managing data
This chapter covers
- Examining the lifecycle and states of objects
- Working with the EntityManager interface
- Working with the Jakarta Persistence API
- Working with detached state
You now understand how ORM solves the static aspects of the object/relational mismatch. With what you know so far, you can create a mapping between Java classes and an SQL schema, solving the structural mismatch problem. We remind that the paradigm mismatch covers the problems of granularity, inheritance, identity, association, and data navigation. For a deeper review, see section 1.2.
An efficient application solution requires something more: you must investigate strategies for runtime data management. These strategies are crucial to the performance and correct behavior of the applications.
In this chapter, we analyze the life cycle of entity instances—how an instance becomes persistent, and how it stops being considered persistent—and the method calls and management operations that trigger these transitions. The JPA EntityManager is the primary interface for accessing data.
Before we look at the API, let’s start with entity instances, their life cycle, and the events that trigger a change of state. Although some of the material may be formal, a solid understanding of the persistence life cycle is essential.