[Java] [JPA] @Inheritance example

@Inheritance.jpg

AbstractProduct.java

import javax.persistence.*;

@Entity

// TABLE_PER_CLASS can mixed with other strategies.
@Inheritance(strategy = InheritanceType.TABLE_PER_CLASS)
// @DiscriminatorColumn & @DiscriminatorValue are no longer take effect
// @DiscriminatorColumn(name = "PRODUCT_TYPE", discriminatorType = DiscriminatorType.STRING)
// @DiscriminatorValue("PRODUCT")
public abstract class AbstractProduct {
    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    public int id;
    public String name;
    public String description;

    ...
}

Book.java

import javax.persistence.*;

@Entity
public class Book extends Product {
    public int isbn;
    public String title;
    public String author;

    ...
}

CompactDisc.java

import javax.persistence.*;

@Entity
public class CompactDisc extends Product {
    public String title;
    public String artist;

    ...
}

ER Diagram.png

Product.java

import javax.persistence.*;

@Entity
public class Product extends AbstractProduct {
    public double price;

    ...
}

TravelGuide.java

import javax.persistence.Entity;

@Entity
public class TravelGuide extends Book {
    public String country;

    ...
}

• SINGLE_TABLE
• JOINED
• TABLE_PER_CLASS
• @MappedSuperclass

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External

• DataNucleus