Hibernate复合主键
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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：
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"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
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 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;
}
// 必须重新定义equals()与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;
// 复合主键类的对应类别必须实作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;
}
// 必须重新定义equals()与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()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
<?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：
User user = new User();
user.setName("bush");
user.setPhone("0970123456");
Session session = 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();
user.setName("bush");
user.setPhone("0970123456");
Session session = 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
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();
}
}
现在User类别的主键信息被分离出来了，例如：
User.java
package onlyfun.caterpillar;
import java.io.Serializable;
public class User implements Serializable {
private UserPK userPK; // 主键
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; // 主键
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，需要指定主键类的信息，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>
在查询数据时，必须指定主键信息，例如：
UserPK pk = new UserPK();
pk.setName("bush");
pk.setPhone("0970123456");
Session session = sessionFactory.openSession();
// 以主键类实例设定复合主键并加载对应的数据
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();
// 以主键类实例设定复合主键并加载对应的数据
User user = (User) session.load(User.class, pk);
System.out.println(user.getAge() + "/t" +
user.getUserPK().getName() + "/t" +
user.getUserPK().getPhone());
session.close();
