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 is one that is not synchronized with the database; any changes in the entity state will not be reflected to the database. The persistence provider does not track any changes that occur to the entity.

As you will see later, by performing the different CRUD operations supported by...