類之間關聯的Hibernate表現
在Java程序中,類之間存在多種包含關系,典型的三種關聯關系有:一個類擁有另一個類的成員,一個類擁有另一個類的集合的成員;兩個類相互擁有對象的集合的成員.在Hibernate中,我們可以使用映射文件中的many-to-one, one-to-many, many-to-many來實現它們.這樣的關系在Hibernate中簡稱為多對一,一對多和多對多.
多對一的類代碼
事件與地點是典型的多對一關系,多個事件可以在一個地點發生(時間不同),一個地點可發生多個事件.它們的對應關系是(多)事件對(一)地點.
兩個類的代碼如右:
public class Event{
private String id;
private String name;
private Location location;
}
public class Location{
private String id;
private String name;
}
多對一的映射文件
<?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="org.hibernate.auction">
<class name="com.sitinspring.domain.Event"
table="Event_TB">
<id name="id" column="ID" >
<generator class="uuid.hex"/>
</id>
<property name="name" column="name" />
<many-to-one name="location" column="locationId" class="com.sitinspring.domain.Location"/>
</class>
</hibernate-mapping>
<?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="org.hibernate.auction">
<class name="com.sitinspring.domain.Location"
table="Location_TB">
<id name="id" column="ID" >
<generator class="uuid.hex"/>
</id>
<property name="name" column="name" />
</class>
</hibernate-mapping>
多對一的表數據
一對多的類代碼
如果一個用戶有多個權限,那么User類和Privilege類就構成了一對多的關系,User類將包含一個Privilege類的集合.
public class User{
private String id;
private String name;
private Set<Privilege> privileges=new LinkedHashSet<Privilege>();
}
public class Privilege{
private String id;
private String userId;
private int privilegeLevel;
}
一對多的映射文件
<?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="org.hibernate.auction">
<class name="com.sitinspring.domain.User"
table="User_TB">
<id name="id" column="ID" >
<generator class="uuid.hex"/>
</id>
<property name="name" column="name" />
<set name="privileges">
<key column="userId"/>
<one-to-many class="com.sitinspring.domain.Privilege"/>
</set>
</class>
</hibernate-mapping>
<?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="org.hibernate.auction">
<class name="com.sitinspring.domain.Privilege"
table="Privilege_TB">
<id name="id" column="ID" >
<generator class="uuid.hex"/>
</id>
<property name="userId" column="userId" />
<property name="privilegeLevel" column="privilegeLevel" />
</class>
</hibernate-mapping>
一對多的表數據
多對多
多對多關系 是指兩個類相互擁有對方的集合,如文章和標簽兩個類,一篇文章可能有多個標簽,一個標簽可能對應多篇文章.要實現這種關系需要一個中間表的輔助.
類代碼如右:
public class Article{
private String id;
private String name;
private Set<Tag> tags = new HashSet<Tag>();
}
public class Tag{
private String id;
private String name;
private Set<Article> articles = new HashSet<Article>();
}
多對多的映射文件
<?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="org.hibernate.auction">
<class name="com.sitinspring.domain.Article" table="ARTICLE_TB">
<id name="id" column="ID" >
<generator class="uuid.hex"/>
</id>
<property name="name" column="NAME" />
<set name="tags" table="ARTICLETAG_TB" cascade="all" lazy="false">
<key column="ARTICLEID" />
<many-to-many column="TAGID" class="com.sitinspring.domain.Tag" />
</set>
</class>
</hibernate-mapping>
<?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="org.hibernate.auction">
<class name="com.sitinspring.domain.Tag" table="TAG_TB">
<id name="id" column="ID" >
<generator class="uuid.hex"/>
</id>
<property name="name" column="NAME" />
<set name="articles" table="ARTICLETAG_TB" cascade="all" lazy="false">
<key column="TAGID" />
<many-to-many column="ARTICLEID" class="com.sitinspring.domain.Article" />
</set>
</class>
</hibernate-mapping>
多對多的表數據
源碼下載：
http://www.aygfsteel.com/Files/junglesong/HibernateMapping20080430203526.rar