基於業務需求,您會需要使用兩個字段來作複合主鍵,例如在User 數據表中,您也許會使用"name" 與"phone" 兩個字段來定義複合主鍵。
假設您這麼建立User 表格:
CREATE
TABLE
user
(
name VARCHAR ( 100 ) NOT NULL ,
phone VARCHAR ( 50 ) NOT NULL ,
age INT ,
PRIMARY KEY (name, phone)
);
name VARCHAR ( 100 ) NOT NULL ,
phone VARCHAR ( 50 ) NOT NULL ,
age INT ,
PRIMARY KEY (name, phone)
);
在表格中,"name" 與"age" 被定義爲複合主鍵,在映像時,可以通過兩種方式來確定複合主鍵。
方式一:基於實體類的複合主鍵,您可以讓User 類別直接帶有"name" 與"age" 這兩個屬性,而Hibernate 要求複合主鍵類別要實作Serializable 接口,並定義equals() 與hashCode() 方法:
User.java
package
onlyfun.caterpillar;
import java.io.Serializable;
import org.apache.commons.lang.builder.EqualsBuilder;
import org.apache.commons.lang.builder.HashCodeBuilder;
// 複合主鍵類的對應類別必須實作Serializable接口
public class User implements Serializable {
private String name;
private String phone;
private Integer age;
public User() {
}
public Integer getAge() {
return age;
}
public void setAge(Integer age) {
this .age = age;
}
public String getName() {
return name;
}
public void setName(String name) {
this .name = name;
}
public String getPhone() {
return phone;
}
public void setPhone(String phone) {
this .phone = phone;
}
// 必須重新定義equals()與hashCode()
public boolean equals(Object obj) {
if (obj == this ) {
return true ;
}
if ( ! (obj instanceof User)) {
return false ;
}
User user = (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();
}
}
import java.io.Serializable;
import org.apache.commons.lang.builder.EqualsBuilder;
import org.apache.commons.lang.builder.HashCodeBuilder;
// 複合主鍵類的對應類別必須實作Serializable接口
public class User implements Serializable {
private String name;
private String phone;
private Integer age;
public User() {
}
public Integer getAge() {
return age;
}
public void setAge(Integer age) {
this .age = age;
}
public String getName() {
return name;
}
public void setName(String name) {
this .name = name;
}
public String getPhone() {
return phone;
}
public void setPhone(String phone) {
this .phone = phone;
}
// 必須重新定義equals()與hashCode()
public boolean equals(Object obj) {
if (obj == this ) {
return true ;
}
if ( ! (obj instanceof User)) {
return false ;
}
User user = (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() 與hashCode() 方法被用作兩筆不同數據的識別依據;接着您可以使用<composite-id> 在映射文件中定義複合主鍵與對象的屬性對應:
User.hbm.xml
<?
xml version="1.0" encoding="utf-8"
?>
<! DOCTYPE hibernate-mapping
PUBLIC "-//Hibernate/Hibernate Mapping DTD 3.0//EN"
"http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd" >
< hibernate-mapping >
< class name ="onlyfun.caterpillar.User" table ="user" >
< composite-id >
< key-property name ="name"
column ="name"
type ="java.lang.String" />
< key-property name ="phone"
column ="phone"
type ="java.lang.String" />
</ composite-id >
< property name ="age" column ="age" type ="java.lang.Integer" />
</ class >
</ hibernate-mapping >
<! DOCTYPE hibernate-mapping
PUBLIC "-//Hibernate/Hibernate Mapping DTD 3.0//EN"
"http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd" >
< hibernate-mapping >
< class name ="onlyfun.caterpillar.User" table ="user" >
< composite-id >
< key-property name ="name"
column ="name"
type ="java.lang.String" />
< key-property name ="phone"
column ="phone"
type ="java.lang.String" />
</ composite-id >
< property name ="age" column ="age" type ="java.lang.Integer" />
</ class >
</ hibernate-mapping >
在儲存數據方面,複合主鍵的儲存沒什麼區別,現在的問題在於如何依據複合主鍵來查詢數據,例如使用load() 方法,您可以創建一個User 實例,並設定複合主鍵對應的屬性,接着再透過load() 查詢對應的數據,例如:
User user
=
new
User();
user.setName( " bush " );
user.setPhone( " 0970123456 " );
Session session = sessionFactory.openSession();
// 以實例設定複合主鍵並加載對應的數據
user = (User) session.load(User. class , user);
System.out.println(user.getAge() + " /t " +
user.getName() + " /t " +
user.getPhone());
session.close();
user.setName( " bush " );
user.setPhone( " 0970123456 " );
Session session = sessionFactory.openSession();
// 以實例設定複合主鍵並加載對應的數據
user = (User) session.load(User. class , user);
System.out.println(user.getAge() + " /t " +
user.getName() + " /t " +
user.getPhone());
session.close();
方式二:通過定義主鍵類來實現,可以將主鍵的信息獨立爲一個類, 而Hibernate 要求自定義的主鍵類要實現Serializable 接口,並定義equals() 與hashCode() 方法 例如:
UserPK.java
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 String name;
private String phone;
public String getName() {
return name;
}
public void setName(String name) {
this .name = name;
}
public String getPhone() {
return phone;
}
public void setPhone(String phone) {
this .phone = phone;
}
public boolean equals(Object obj) {
if (obj == this ) {
return true ;
}
if ( ! (obj instanceof User)) {
return false ;
}
UserPK pk = (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();
}
}
import java.io.Serializable;
import org.apache.commons.lang.builder.EqualsBuilder;
import org.apache.commons.lang.builder.HashCodeBuilder;
public class UserPK implements Serializable {
private String name;
private String phone;
public String getName() {
return name;
}
public void setName(String name) {
this .name = name;
}
public String getPhone() {
return phone;
}
public void setPhone(String phone) {
this .phone = phone;
}
public boolean equals(Object obj) {
if (obj == this ) {
return true ;
}
if ( ! (obj instanceof User)) {
return false ;
}
UserPK pk = (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();
}
}
現在User 類別的主鍵信息被分離出來了,例如:
User.java
package
onlyfun.caterpillar;
import java.io.Serializable;
public class User implements Serializable {
private UserPK userPK; // 主鍵
private Integer age;
public User() {
}
public UserPK getUserPK() {
return userPK;
}
public void setUserPK(UserPK userPK) {
this .userPK = userPK;
}
public Integer getAge() {
return age;
}
public void setAge(Integer age) {
this .age = age;
}
}
import java.io.Serializable;
public class User implements Serializable {
private UserPK userPK; // 主鍵
private Integer age;
public User() {
}
public UserPK getUserPK() {
return userPK;
}
public void setUserPK(UserPK userPK) {
this .userPK = userPK;
}
public Integer getAge() {
return age;
}
public void setAge(Integer age) {
this .age = age;
}
}
在映像文件方面,需要指定主鍵類的信息,例如:
User.hbm.xml
<?
xml version="1.0" encoding="utf-8"
?>
<! DOCTYPE hibernate-mapping
PUBLIC "-//Hibernate/Hibernate Mapping DTD 3.0//EN"
"http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd" >
< hibernate-mapping >
< class name ="onlyfun.caterpillar.User" table ="user" >
< composite-id name ="userPK"
class ="onlyfun.caterpillar.UserPK"
unsaved-value ="any" >
< key-property name ="name"
column ="name"
type ="java.lang.String" />
< key-property name ="phone"
column ="phone"
type ="java.lang.String" />
</ composite-id >
< property name ="age" column ="age" type ="java.lang.Integer" />
</ class >
</ hibernate-mapping >
<! DOCTYPE hibernate-mapping
PUBLIC "-//Hibernate/Hibernate Mapping DTD 3.0//EN"
"http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd" >
< hibernate-mapping >
< class name ="onlyfun.caterpillar.User" table ="user" >
< composite-id name ="userPK"
class ="onlyfun.caterpillar.UserPK"
unsaved-value ="any" >
< key-property name ="name"
column ="name"
type ="java.lang.String" />
< key-property name ="phone"
column ="phone"
type ="java.lang.String" />
</ composite-id >
< property name ="age" column ="age" type ="java.lang.Integer" />
</ class >
</ hibernate-mapping >
在查詢數據時,必須指定主鍵信息,例如:
UserPK pk
=
new
UserPK();
pk.setName( " bush " );
pk.setPhone( " 0970123456 " );
Session session = sessionFactory.openSession();
// 以主鍵類實例設定複合主鍵並加載對應的數據
User user = (User) session.load(User. class , pk);
System.out.println(user.getAge() + " /t " +
user.getUserPK().getName() + " /t " +
user.getUserPK().getPhone());
session.close();
pk.setName( " bush " );
pk.setPhone( " 0970123456 " );
Session session = sessionFactory.openSession();
// 以主鍵類實例設定複合主鍵並加載對應的數據
User user = (User) session.load(User. class , pk);
System.out.println(user.getAge() + " /t " +
user.getUserPK().getName() + " /t " +
user.getUserPK().getPhone());
session.close();