Hibernate承袭策略

Hibernate继承策略

Hibernate继承策略总共有三种，一种是共用一张表，一种是每个类一张表，还有一种是通过表连接的方式：

第一种方式，即共用一张表：

@Entity
@Inheritance(strategy=InheritanceType.SINGLE_TABLE)
@DiscriminatorColumn(name="discriminator", discriminatorType=DiscriminatorType.STRING)//表示区分不同的对象的字段名
@DiscriminatorValue("person")//用来表示该对象是何种对象的,即区分器
public class Parent {
	private int id;
	private String name;
	
	@Id
	@GeneratedValue
	public int getId() {
		return id;
	}
	public void setId(int id) {
		this.id = id;
	}
	public String getName() {
		return name;
	}
	public void setName(String name) {
		this.name = name;
	}

}

@Entity
@DiscriminatorValue("child1")
public class Child1 extends Parent {
	private String email;

	public String getEmail() {
		return title;
	}

	public void setEmail(String email) {
		this.email = email;
	}

	
}



@Entity
@DiscriminatorValue("child2")
public class Child2 extends Parent {
	
	private String address;

	public String getAddress() {
		return score;
	}

	public void setAddress(String address) {
		this.address = address;
	}
	
}

 

 

第二种策略是每个类一张表：

@Entity
@Inheritance(strategy=InheritanceType.TABLE_PER_CLASS)
@TableGenerator(		//一个类一张表，最重要的是要保证它们的id由一个生成器产生，@TableGenerator就是为了控制这个的
		name="t_gen",
		table="t_gen_table",
		pkColumnName="t_pk",
		valueColumnName="t_value",
		pkColumnValue="person_pk",
		initialValue=1,
		allocationSize=1
		)
public class Parent {
	private int id;
	private String name;
	
	@Id
	@GeneratedValue(generator="t_gen", strategy=GenerationType.TABLE)//这个就是用表生成器生成的，用同一个生成器就可以控制它们的id不重复
	public int getId() {
		return id;
	}
	public void setId(int id) {
		this.id = id;
	}
	public String getName() {
		return name;
	}
	public void setName(String name) {
		this.name = name;
	}

}


@Entity
public class Child2 extends Parent {
	
	private String address;

	public String getAddress() {
		return score;
	}

	public void setAddress(String address) {
		this.address = address;
	}
	
}


@Entity
public class Child1 extends Parent {
	private String email;

	public String getEmail() {
		return title;
	}

	public void setEmail(String email) {
		this.email = email;
	}

	
}

 

 

弟三种方式是采用表连接的方式：

@Entity
@Inheritance(strategy=InheritanceType.JOINED)

public class Parent {
	private int id;
	private String name;
	
	@Id
	@GeneratedValue
	public int getId() {
		return id;
	}
	public void setId(int id) {
		this.id = id;
	}
	public String getName() {
		return name;
	}
	public void setName(String name) {
		this.name = name;
	}

}

@Entity
public class Child2 extends Parent {
	
	private String address;

	public String getAddress() {
		return score;
	}

	public void setAddress(String address) {
		this.address = address;
	}
	
}


@Entity
public class Child1 extends Parent {
	private String email;

	public String getEmail() {
		return title;
	}

	public void setEmail(String email) {
		this.email = email;
	}

	
}