(8) EBJ Learning: Single_table,joined,table_per_class Three inheritance strategies for JPA

One: single_table inheritance Policy

Animal.java

Import java.io.Serializable;

Import Javax.persistence.DiscriminatorColumn;
Import Javax.persistence.DiscriminatorValue;
Import javax.persistence.Entity;
Import Javax.persistence.GeneratedValue;
Import Javax.persistence.Id;
Import javax.persistence.Inheritance;
Import Javax.persistence.InheritanceType;

/**
 * The single table inherits a * */
@Entity
@Inheritance (strategy=inheritancetype.single_table)//specified as single table inheritance
@ Discriminatorcolumn (name= "Animaltype")//Identification field definition
@DiscriminatorValue ("A")//identity of the class public
class Animal {
  @Id
  @GeneratedValue
  private int Id;
  private String name;
  Private String sex;
}

Bird.java

Import Javax.persistence.DiscriminatorValue;
Import javax.persistence.Entity;

@Entity
@DiscriminatorValue ("B") public
class Bird extends animal{
  private int height;
}

Pig.java

Import Javax.persistence.DiscriminatorValue;
Import javax.persistence.Entity;

@Entity
@DiscriminatorValue ("P") public
class Pig extends Animal {
  private int weight;
}

The final table structure

Two Join mappings

Animal.java

Import java.io.Serializable;

Import Javax.persistence.DiscriminatorColumn;
Import Javax.persistence.DiscriminatorValue;
Import javax.persistence.Entity;
Import Javax.persistence.GeneratedValue;
Import Javax.persistence.Id;
Import javax.persistence.Inheritance;
Import Javax.persistence.InheritanceType;

/**
 * Join Map
 * Parent class, subclass corresponds to different table, only special attributes of its extension exist in subclasses (no attributes of parent class)
 * 
 *
/@Entity @Inheritance ( strategy=inheritancetype.joined)//specified as single-table inherit public
class Animal {
  @Id
  @GeneratedValue
  Private int id;
  private String name;
  Private String sex;
}

Bird.java

Import javax.persistence.Entity;

@Entity public
class Bird extends Animal {
  private int height;
}

The final table structure

Three Table_per_class

Animal.java

Import java.io.Serializable;

Import Javax.persistence.DiscriminatorColumn;
Import Javax.persistence.DiscriminatorValue;
Import javax.persistence.Entity;
Import Javax.persistence.GeneratedValue;
Import Javax.persistence.Id;
Import javax.persistence.Inheritance;
Import Javax.persistence.InheritanceType;

/**
 * Table_per_class Policy: Parent class and subclass correspond to different tables, all attributes exist in subclass
 * (contains all attributes inherited from parent Class) * */
@Entity
@ Inheritance (strategy=inheritancetype.table_per_class) public 
CLASS Animal {
  @Id
//  @ Generatedvalue (when using Table_per_class, cannot use generatedvalue)
  private int id;
  private String name;
  Private String sex;
}

Bird.java

Import javax.persistence.Entity;

@Entity public
class Bird extends Animal {
  private int height;
}

The final table structure