Performing CRUD operations

In the following sections, we are going to learn how to use JPA for performing the four basic data access operations: creating, retrieving, updating, and deleting entities.

Managed versus detached entities

One of the most important concepts to understand about the JPA framework is that every entity has a state at each point during runtime. An entity can be in one of two states:

• Managed: A managed entity is one that is synchronized with the database; any changes in the entity state will be reflected in the database. In other words, the persistence provider is tracking a managed entity state, and keeps updating the database with any changes that occur to its state.
• Detached: A detached entity...