Step 2: Define a JPA Entity Class
To store objects in an ObjectDB database using JPA we need to define an entity class:
- Open the [New Java Class] dialog box, e.g. by right clicking the tutorial package node
(in the [Projects] window) and selecting New > Java Class...
- Enter Point as the class name - use exactly that case sensitive class name.
- The package name should be tutorial.
- Click Finish to create the new class.
Use copy and paste to fill the new source file with the following content:
package tutorial;
import java.io.Serializable;
import javax.persistence.*;
@Entity
public class Point implements Serializable {
private static final long serialVersionUID = 1L;
@Id @GeneratedValue
private long id;
private int x;
private int y;
public Point() {
}
Point(int x, int y) {
this.x = x;
this.y = y;
}
public Long getId() {
return id;
}
public int getX() {
return x;
}
public int getY() {
return y;
}
@Override
public String toString() {
return String.format("(%d, %d)", this.x, this.y);
}
}
The new class should represent Point
objects in the database. Besides the @Entityjavax.persistence.EntityJPA annotationSpecifies that the class is an entity.See JavaDoc Reference Page... annotation and the id
field (and its annotations) - the Point
class is an ordinary Java class.
The warning that NetBeans displays on the Guest
class indicates that a persistence unit definition in an XML file is missing. This is discussed in the ObjectDB Manual. But nevertheless, this class is a valid ObjectDB entity class, despite the warning.
The next step is adding a Main class that stores and retrieves instances of the Point
entity class.