Mapping Entities in Hibernate

Alrighty then, let's map some entities to database tables, or as I like to call it, teaching your code to speak 'Database-ese'!

First, we need to define what a Entity is. In the world of JPA (Java Persistence API) and Hibernate, an Entity is just a fancy name for a plain old Java object (also known as a POJO) that we're going to store in a database.

Here is an example of a Book entity:

@Entity
@Table(name = "books")
public class Book {

    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    private Long id;

    @Column(name = "title")
    private String title;

    @Column(name = "author")
    private String author;

    // getters and setters
}

Let's break down the hieroglyphics above:

@Entity: This tells Hibernate that this class is an entity and needs to be managed by the entity manager. It's like the flashing neon sign that says "Hey, I'm important and I need to be in the database!"
@Table(name = "books"): Here, we're specifying which table in the database this entity corresponds to. If you don't use this annotation, Hibernate will just use the class name as the table name. But we're control freaks and we like to be specific!
@Id: This annotation is telling Hibernate which field we're using as the primary key in the database. It's the equivalent of wearing a giant hat with "I'm Number 1!" in a crowd.
@GeneratedValue(strategy = GenerationType.IDENTITY): We're telling Hibernate to let the database decide how to generate values for the id field. That way, we don't have to keep count ourselves (we've got better things to do!).
@Column(name = "title"): With this, we're mapping the title field in our class to the title column in our books table. It's like introducing your code to the database column: "Title, meet Title".

And voila! We've mapped a Java class to a database table, like a pro! Now, whenever you use this entity, Hibernate will automatically know which table it corresponds to and what the column names are. Isn't that swell? We've done more mapping than a cartographer with a caffeine addiction!