继承关联关系

最新推荐文章于 2024-02-19 10:39:27 发布

转载最新推荐文章于 2024-02-19 10:39:27 发布 · 767 阅读

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本文探讨了在ORM框架中如何实现不同类型的多表关联映射，包括单表继承、联合子类以及多表继承的方式，并提供了具体的XML配置示例。

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论坛（主题Topic和回复Reply继承文章Article）

Article.java

package com.domain;

public class Article {
	private Integer id;
	private String content;
	public Integer getId() {
		return id;
	}
	public void setId(Integer id) {
		this.id = id;
	}
	public String getContent() {
		return content;
	}
	public void setContent(String content) {
		this.content = content;
	}
	
}

Topic.java

package com.domain;

public class Topic extends Article{
	private Integer type;
	public Integer getType() {
		return type;
	}
	public void setType(Integer type) {
		this.type = type;
	}

}

Reply.jva

package com.domain;

public class Reply extends Article{
	private Integer level;

	public Integer getLevel() {
		return level;
	}

	public void setLevel(Integer level) {
		this.level = level;
	}
}

1、所有的数据保存在一张表的情况(Article.hbm.xml)

<?xml version="1.0"?>
<!DOCTYPE hibernate-mapping PUBLIC 
	"-//Hibernate/Hibernate Mapping DTD 3.0//EN"
	"http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd">
<hibernate-mapping package="com.domain">

	<class name="Article" table="article" discriminator-value="article">		
		<id name="id">
			<generator class="native"/>
		</id>
		<discriminator column="kind" type="string"></discriminator>
		<property name="content" column="content"/>
		<subclass name="Topic" discriminator-value="topic">
			<property name="type"></property>
		</subclass>
		<subclass name="Reply" discriminator-value="reply">
			<property name="level"></property>
		</subclass>
	</class>
	
</hibernate-mapping>

2、三张表的情况

<?xml version="1.0"?>
<!DOCTYPE hibernate-mapping PUBLIC 
	"-//Hibernate/Hibernate Mapping DTD 3.0//EN"
	"http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd">
<hibernate-mapping package="com.domain">

	<class name="Article" table="article">		
		<id name="id">
			<generator class="native"/>
		</id>
		<property name="content" column="content"/>
		<joined-subclass name="Topic" table="topic">
			<key column="id"></key>
			<property name="type"></property>
		</joined-subclass>
		<joined-subclass name="Reply" table="reply">
			<key column="id"></key>
			<property name="level"></property>
		</joined-subclass>
	</class>
	
</hibernate-mapping>

3、两张表的情况

<?xml version="1.0"?>
<!DOCTYPE hibernate-mapping PUBLIC 
	"-//Hibernate/Hibernate Mapping DTD 3.0//EN"
	"http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd">
<hibernate-mapping package="com.domain">

	<class name="Article" abstract="true">		
		<id name="id">
			<generator class="increment"/>
		</id>
		<property name="content" column="content"/>
		<union-subclass name="Topic" table="topic">
			<property name="type"></property>
		</union-subclass>
		<union-subclass name="Reply" table="reply">
			<property name="level"></property>
		</union-subclass>
	</class>
	
</hibernate-mapping>