hibernate 复合主键

基于业务需求，您会需要使用两个字段来作复合主键，例如在User数据表中，您也许会使用"name"与"phone"两个字段来定义复合主键。

假设您这么建立User表格：

<!--<br><br>Code highlighting produced by Actipro CodeHighlighter (freeware)<br>http://www.CodeHighlighter.com/<br><br>--> CREATE TABLE user ( name VARCHAR ( 100 ) NOT NULL , phone VARCHAR ( 50 ) NOT NULL , age INT , PRIMARY KEY (name,phone) );

在表格中，"name"与"age"被定义为复合主键，在映像时，您可以让User类别直接带有"name"与"age"这两个属性，而Hibernate要求复合主键类别要实作Serializable接口，并定义equals()与hashCode()方法：

User.java

<!--<br><br>Code highlighting produced by Actipro CodeHighlighter (freeware)<br>http://www.CodeHighlighter.com/<br><br>--> package onlyfun.caterpillar; import java.io.Serializable; import org.apache.commons.lang.builder.EqualsBuilder; import org.apache.commons.lang.builder.HashCodeBuilder; // 复合主键类的对应类别必须实作Serializable接口 public class User implements Serializable{ private Stringname; private Stringphone; private Integerage; public User(){ } public IntegergetAge(){ return age; } public void setAge(Integerage){ this .age = age; } public StringgetName(){ return name; } public void setName(Stringname){ this .name = name; } public StringgetPhone(){ return phone; } public void setPhone(Stringphone){ this .phone = phone; } // 必须重新定义equals()与hashCode() public boolean equals(Objectobj){ if (obj == this ){ return true ; } if ( ! (obj instanceof User)){ return false ; } Useruser = (User)obj; return new EqualsBuilder() .append( this .name,user.getName()) .append( this .phone,user.getPhone()) .isEquals(); } public int hashCode(){ return new HashCodeBuilder() .append( this .name) .append( this .phone) .toHashCode(); } }

equals()与hashCode()方法被用作两笔不同数据的识别依据；接着您可以使用<composite-id>在映射文件中定义复合主键与对象的属性对应：

User.hbm.xml

<!--<br><br>Code highlighting produced by Actipro CodeHighlighter (freeware)<br>http://www.CodeHighlighter.com/<br><br>--><?xmlversion="1.0"encoding="utf-8"?> <!DOCTYPEhibernate-mapping PUBLIC"-//Hibernate/HibernateMappingDTD3.0//EN"

"http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd">

<hibernate-mapping>

<classname="onlyfun.caterpillar.User"table="user">

<composite-id>

<key-propertyname="name" column="name" type="java.lang.String"/>

<key-propertyname="phone" column="phone" type="java.lang.String"/>

</composite-id>

<propertyname="age"column="age"type="java.lang.Integer"/>

</class>

</hibernate-mapping>

在储存数据方面，复合主键的储存没什么区别，现在的问题在于如何依据复合主键来查询数据，例如使用load()方法，您可以创建一个User实例，并设定复合主键对应的属性，接着再透过load()查询对应的数据，例如：

<!--<br><br>Code highlighting produced by Actipro CodeHighlighter (freeware)<br>http://www.CodeHighlighter.com/<br><br>--> Useruser = new User(); user.setName( " bush " ); user.setPhone( " 0970123456 " ); Sessionsession = sessionFactory.openSession(); // 以实例设定复合主键并加载对应的数据 user = (User)session.load(User. class ,user); System.out.println(user.getAge() + " \t " + user.getName() + " \t " + user.getPhone()); session.close();

可以将主键的信息独立为一个类别，例如：

UserPK.java

<!--<br><br>Code highlighting produced by Actipro CodeHighlighter (freeware)<br>http://www.CodeHighlighter.com/<br><br>--> package onlyfun.caterpillar; import java.io.Serializable; import org.apache.commons.lang.builder.EqualsBuilder; import org.apache.commons.lang.builder.HashCodeBuilder; public class UserPK implements Serializable{ private Stringname; private Stringphone; public StringgetName(){ return name; } public void setName(Stringname){ this .name = name; } public StringgetPhone(){ return phone; } public void setPhone(Stringphone){ this .phone = phone; } public boolean equals(Objectobj){ if (obj == this ){ return true ; } if ( ! (obj instanceof User)){ return false ; } UserPKpk = (UserPK)obj; return new EqualsBuilder() .append( this .name,pk.getName()) .append( this .phone,pk.getPhone()) .isEquals(); } public int hashCode(){ return new HashCodeBuilder() .append( this .name) .append( this .phone) .toHashCode(); } }

现在User类别的主键信息被分离出来了，例如：

User.java

<!--<br><br>Code highlighting produced by Actipro CodeHighlighter (freeware)<br>http://www.CodeHighlighter.com/<br><br>--> package onlyfun.caterpillar; import java.io.Serializable; public class User implements Serializable{ private UserPKuserPK; // 主键 private Integerage; public User(){ } public UserPKgetUserPK(){ return userPK; } public void setUserPK(UserPKuserPK){ this .userPK = userPK; } public IntegergetAge(){ return age; } public void setAge(Integerage){ this .age = age; } }

在映像文件方面，需要指定主键类的信息，例如：

User.hbm.xml

<!--<br><br>Code highlighting produced by Actipro CodeHighlighter (freeware)<br>http://www.CodeHighlighter.com/<br><br>--><?xmlversion="1.0"encoding="utf-8"?> <!DOCTYPEhibernate-mapping PUBLIC"-//Hibernate/HibernateMappingDTD3.0//EN"

"http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd">

<hibernate-mapping>

<classname="onlyfun.caterpillar.User"table="user">

<composite-idname="userPK" class="onlyfun.caterpillar.UserPK" unsaved-value="any">

<key-propertyname="name" column="name" type="java.lang.String"/>

<key-propertyname="phone" column="phone" type="java.lang.String"/>

</composite-id>

<propertyname="age"column="age"type="java.lang.Integer"/>

</class>

</hibernate-mapping>

在查询数据时，必须指定主键信息，例如：

<!--<br><br>Code highlighting produced by Actipro CodeHighlighter (freeware)<br>http://www.CodeHighlighter.com/<br><br>--> UserPKpk = new UserPK(); pk.setName( " bush " ); pk.setPhone( " 0970123456 " ); Sessionsession = sessionFactory.openSession(); // 以主键类实例设定复合主键并加载对应的数据 Useruser = (User)session.load(User. class ,pk); System.out.println(user.getAge() + " \t " + user.getUserPK().getName() + " \t " + user.getUserPK().getPhone()); session.close();