Hibernate使用注解，继承映射写法

继承映射在 Annotation 中使用 @Inheritance 注解，并且需要使用 strategy 属性指定继承策略，继承策略有 SINGLE_TABLE、TABLE_PER_CLASS 和 JOINED 三种。

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一、SINGLE_TABLE

SINGLE_TABLE 是将父类和其所有的子类集合在一块，存在一张表中，并创建一个新的字段来判断对象的类型。

Person.java：

<div>
package com.getop.sales.model;

import javax.persistence.*;

/**
 * 
 * @ClassName: Person
 * @Description: 人类
 * @author LiYun
 * @date 2014-8-19 下午6:01:55
 * 
 */
@Entity
@Table(name = "SALES_PERSON")
@Inheritance(strategy = InheritanceType.SINGLE_TABLE)
@DiscriminatorColumn(name = "discriminator", discriminatorType = DiscriminatorType.STRING)
@DiscriminatorValue("person")
public class Person {

	private Integer id;
	private String name;

	@Id
	@Column(name = "id")
	@SequenceGenerator(name = "SALES_PERSON_ID", sequenceName = "SALES_PERSON_ID", allocationSize = 1, initialValue = 1)
	@GeneratedValue(strategy = GenerationType.SEQUENCE, generator = "SALES_PERSON_ID")
	public Integer getId() {

		return id;
	}

	public void setId(Integer id) {

		this.id = id;
	}

	public String getName() {

		return name;
	}

	public void setName(String name) {

		this.name = name;
	}

}
</div>

@Inheritance 的 strategy 属性是指定继承关系的生成策略，@DiscriminatorColumn 注解作用是指定生成的新的判断对象类型的字段的名称和类型，@DiscriminatorValue 注解是确定此类（Person）的标示，即 DiscriminatorColumn 的值。

Student.java：

<div>
package com.getop.sales.model;

import javax.persistence.*;

@Entity
@DiscriminatorValue("student")
public class Student extends Person {

	private Integer score;

	public Integer getScore() {

		return score;
	}

	public void setScore(Integer score) {

		this.score = score;
	}

}
</div>

Teacher.java：

<div>
package com.getop.sales.model;

import javax.persistence.*;

@Entity
@DiscriminatorValue("teacher")
public class Teacher extends Person {

	private String title;

	public String getTitle() {

		return title;
	}

	public void setTitle(String title) {

		this.title = title;
	}

}
</div>

生成的数据库表如下：

存入数据后结构如下：

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二、TABLE_PER_CLASS

TABLE_PER_CLASS 是为每一个类创建一个表，这些表是相互独立的。

Person.java：

<span class="lnum" style="color: rgb(96, 96, 96); ">   1:  </span>@Entity

   2:  @Inheritance(strategy=InheritanceType.TABLE_PER_CLASS)

<span class="lnum" style="color: rgb(96, 96, 96); ">   3:  </span><span class="kwrd" style="color: rgb(0, 0, 255); ">public</span> <span class="kwrd" style="color: rgb(0, 0, 255); ">class</span> Person {

   4:      @Id

<span class="lnum" style="color: rgb(96, 96, 96); ">   5:  </span>    <span class="kwrd" style="color: rgb(0, 0, 255); ">private</span> <span class="kwrd" style="color: rgb(0, 0, 255); ">int</span> id;

   6:      private String name;

<span class="lnum" style="color: rgb(96, 96, 96); ">   7:  </span><span class="rem" style="color: rgb(0, 128, 0); ">//Getters and setters omitted here...</span>

   8:  }

Student.java：

<span class="lnum" style="color: rgb(96, 96, 96); ">   1:  </span>@Entity

   2:  public class Student extends Person{

<span class="lnum" style="color: rgb(96, 96, 96); ">   3:  </span>    <span class="kwrd" style="color: rgb(0, 0, 255); ">private</span> <span class="kwrd" style="color: rgb(0, 0, 255); ">int</span> score;

   4:  //Getters and setters omitted here...

<span class="lnum" style="color: rgb(96, 96, 96); ">   5:  </span>}

Teacher.java：

<span class="lnum" style="color: rgb(96, 96, 96); ">   1:  </span>@Entity

   2:  public class Teacher extends Person{

<span class="lnum" style="color: rgb(96, 96, 96); ">   3:  </span>    <span class="kwrd" style="color: rgb(0, 0, 255); ">private</span> String title;

   4:  //Getters and setters omitted here...

<span class="lnum" style="color: rgb(96, 96, 96); ">   5:  </span>}

创建的数据库表如下：

 

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三、JOINED

JOINED 是将父类、子类分别存放在不同的表中，并且建立相应的外键，以确定相互之间的关系。

Person.java：

<span class="lnum" style="color: rgb(96, 96, 96); ">   1:  </span>@Entity

   2:  @Inheritance(strategy=InheritanceType.JOINED)

<span class="lnum" style="color: rgb(96, 96, 96); ">   3:  </span><span class="kwrd" style="color: rgb(0, 0, 255); ">public</span> <span class="kwrd" style="color: rgb(0, 0, 255); ">class</span> Person {

   4:      @Id

<span class="lnum" style="color: rgb(96, 96, 96); ">   5:  </span>    @GeneratedValue

   6:      private int id;

<span class="lnum" style="color: rgb(96, 96, 96); ">   7:  </span>    <span class="kwrd" style="color: rgb(0, 0, 255); ">private</span> String name;

   8:  //Getters and setters omitted here...

<span class="lnum" style="color: rgb(96, 96, 96); ">   9:  </span>}

子类中只需声明与父类不同的域即可：

Student.java：

<span class="lnum" style="color: rgb(96, 96, 96); ">   1:  </span>@Entity

   2:  public class Student extends Person{

<span class="lnum" style="color: rgb(96, 96, 96); ">   3:  </span>    <span class="kwrd" style="color: rgb(0, 0, 255); ">private</span> <span class="kwrd" style="color: rgb(0, 0, 255); ">int</span> coat;

   4:  //Getters and setters omitted here...

<span class="lnum" style="color: rgb(96, 96, 96); ">   5:  </span>}

Teacher.java 类似。

生成的数据库表如下：