[Java] [JPA] @Inheritance example

@Inheritance.jpg

Book.java

import javax.persistence.*;

@Entity
@DiscriminatorValue("BOOK")
public class Book extends Product {
    public int isbn;
    public String title;
    public String author;

    ...
}

CompactDisc.java

import javax.persistence.*;

@Entity
@DiscriminatorValue("COMPACT_DISC")
public class CompactDisc extends Product {
    public String title;
    public String artist;

    ...
}

ER Diagram.png

Product.java

// In our example, lets ignore the AbstractProduct class for a moment
// and assume that Product is the base class (with the "id").

import javax.persistence.*;

@Entity
@Inheritance(strategy = InheritanceType.SINGLE_TABLE)   // This is default strategy
@DiscriminatorColumn(name = "PRODUCT_TYPE", discriminatorType = DiscriminatorType.STRING)
@DiscriminatorValue("PRODUCT")  // Default = entity name
public class Product {
    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    public int id;
    public String name;
    public String description;
    public double price;

    ...
}

TravelGuide.java

import javax.persistence.*;

@Entity
@DiscriminatorValue("TRAVEL_GUIDE")
public class TravelGuide extends Book {
    public String country;

    ...
}

• SINGLE_TABLE
• JOINED
• TABLE_PER_CLASS
• @MappedSuperclass

---

External

• DataNucleus