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 project node
  (in the [Projects] window) and selecting New > Java Class...
• Enter Guest as the class name - use exactly that case sensitive class name.

• Enter guest as the package name - use exactly that case sensitive package name.
• Click Finish to create the new class.

Use copy and paste to replace the new source file content with the following code:

package guest;

import java.io.Serializable;
import java.sql.Date;
import javax.persistence.Entity;
import javax.persistence.GeneratedValue;
import javax.persistence.Id;

@Entity
public class Guest implements Serializable {
    private static final long serialVersionUID = 1L;

    // Persistent Fields:
    @Id @GeneratedValue
    Long id;
    private String name;
    private Date signingDate;

    // Constructors:
    public Guest() {
    }

    public Guest(String name) {
        this.name = name;
        this.signingDate = new Date(System.currentTimeMillis());
    }

    // String Representation:
    @Override
    public String toString() {
        return name + " (signed on " + signingDate + ")";
    }
}

The new class should represent Guest objects in the database. Besides the @Entityjavax.persistence.Entity (JPA Annotation)Specifies that the class is an entity. annotation and the id field (and its annotations) - the Guest 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 context listener class that will manage a JPA's EntityManagerFactory representing the ObjectDB database.